Final Report
to the
Office of Preservation
National Endowment for the Humanities
Enclosures and Air Pollution in Image
Preservation
Grant # PS-20741-93
Edward Zinn, James M. Reilly, and Douglas W. Nishimura
Image Permanence Institute
November 24, 1997
Table of Contents
Executive Summary..................................................................................................1
Acknowlegments.....................................................................................................3
Introduction............................................................................................................4
Ozone and Objects Indoors................................................................................................... 5
Sulfur Dioxide and Nitrogen Oxides Indoors...................................................................... 7
Enclosures and Air Pollution............................................................................................... 8
Test Apparatus.................................................................................................................... 10
Overview of Test Methodology ............................................................................................ 12
Phase I: Study of Pure Oxidizing Gases at Ambient Conditions..............................12
Phase II: Study of Synergistic Effects......................................................................14
Phase III: Study of Enclosures................................................................................15
How Incubation Conditions Relate to Real Life............................................................... 21
Results.........................................................................................................................22
Phase I: Study of Pure Oxidizing Gases at Ambient Conditions...................................... 24
0.1 ppm Ozone......................................................................................................25
Color................................................................................................................25
Black-and-White Photographic Materials...........................................................25
0.1 ppm Nitrogen Dioxide.....................................................................................26
Color................................................................................................................26
Base Staining of Print Supports.........................................................................27
Staining of Plastic Enclosures............................................................................28
Black-and-White Photographic Materials...........................................................28
Phase II: Study of Synergistic Effects.................................................................................. 30
Oxidizing/Reducing Gas Mixtures..........................................................................30
Effects of 0.1 ppm NO2 /0.05 ppm SO2, 0.1 ppm O3/0.05 ppm SO2, and
0.1 ppm NO2 /0.05 ppm H2S . ........................................................................30
Color Materials............................................................................................30
Black-and-White Silver Materials..................................................................31
Oxidant Gas Mixtures ............................................................................................31
Effects of 0.1 ppm O3 /0.1 ppm NO2 (Six Months)...........................................31
Color Materials............................................................................................31
Black-and-White Silver Materials..................................................................32
Effects of 0.1 ppm NO2 /0.1 ppm O3 /0.05 ppm H2S (6 Months)......................32
Color Materials in Mixed NO2 /O3/H2S Atmosphere....................................33
Phase III: Study of Enclosures............................................................................................ 34
Paper and Plastic Sleeves.........................................................................................34
Paper and Plastic Sleeve Permeability......................................................................36
Multiple Layers of Sample Material in a Microfilm Storage Box..............................36
Passive Ozone Monitor....................................................................................................... 38
Choosing a Housing...............................................................................................38
The Detector..........................................................................................................39
Detectors in Test Incubations............................................................................40
Detectors Distributed in the Office Space..........................................................40
Conclusions/Plans for Development.......................................................................40
Conclusions..............................................................................................................42
References.................................................................................................................44
Bibliography.............................................................................................................46
Executive Summary
This three-year project, Enclosures and Air Pollution in Image Preservation (PS-20741-93),
built upon the work completed in a previous grant funded by the National Endowment for
the Humanities (NEH), Air Pollution Effects on Library Microforms (PS-20273-89). Although
the earlier project outlined in broad strokes the relative sensitivity of several commonly used
micrographic products to high levels of pollutant gases, it did not attempt to evaluate the potential threat posed to common imaging materials—color and black-and-white photographs
and films—by ambient levels of pollution in libraries and archives. The earlier project also did
not address mixtures of gases or protection offered by common storage enclosures. The current project was broken into three phases to address these issues.
Phase I was a logical continuation of the original NEH-funded program in which pure
oxidants at high concentrations were used to establish susceptibility of various photographic
materials to oxidation. In this new study, pure oxidant gases O3 (ozone) and NO2 (nitrogen
dioxide) were used in a low concentration of 0.1 parts per million (ppm) at ambient temperature (25°C) and humidity (50% RH) to quantify the effects of plausible real-life indoor
concentrations of these gases. Although some of the very sensitive color print materials were
severely faded by these incubations, most of the chromogenic color films and prints were not
affected. Furthermore, aside from some formation of redox blemishes on the direct duplicating film and edge mirroring on the RC prints, most of the silver products resisted attack by
these oxidants.
While the previous project showed that filamentary silver is relatively resistant to the effects
of pure ozone, nitrogen dioxide, and sulfur dioxide, there are numerous real-world examples
of silver images showing image discoloration and/or fading when exposed to an environment
having elevated pollutant levels. In all likelihood, such damage is the result of a combination
of gases and exposure for extended periods of time. Phase II of this study investigated the
interaction of mixed pollutant gases at low concentrations and long incubation periods to determine if there were synergistic effects as a result of the interaction of two or more pollutants
over time. Mixing these gases did produce effects but did not result in the increased activity
that was expected. On the contrary, in most of the mixed-gas experiments, a reduced amount
of fading of the color samples was noted. Apparently an interaction between the individual
gases resulted in a net reduction in the total gas concentrations. This project did not measure
the pollutants absorbed by the samples and did not attempt to study the long-term effects that
these absorbed gases might present.
Phase III sought to evaluate the potential of enclosures for mitigating the effects of pollutants in storage atmospheres. Several commonly available enclosure materials in different
1
configurations were studied to determine the usefulness of each system in blocking the detrimental effects of gaseous attack on the photographic materials stored in them. This phase
incorporated higher concentrations of pollutant gases, both pure gas and mixed atmospheres,
and shorter periods of gas exposure, in order to produce results within a reasonable time. The
results of this work indicate that multiple layers of packaging do impede the diffusion of pollutant gases. Also, the study showed that enclosures made of paper or board do not offer any
long-term protection against high levels of pollutants in the storage environment. This agrees
with work by Charles Guttman at the National Institute of Standards and Technology performed on behalf of the National Archives.1 The atmosphere inside a cardboard enclosure will
reach equilibrium with the outside air in a relatively short time. Enclosure configurations that
block the diffusion of outside air (encapsulation in plastic or sealed metal cans) will protect the
enclosed object from pollutants outside, but they will also trap any deterioration by-products
released by the objects. This could increase the rate of autocatalytic forms of deterioration.
This study also investigated the use of Kodak Ektatherm dye diffusion print material as
the basis for a passive ozone monitor for libraries and archives. Samples of this material were
added to all incubations in the project. A prototype passive ozone monitor was developed
incorporating a disk of the thermal print material as an ozone detector. This medium proved
to be a good indicator of high oxidant levels, 0.1 ppm or more, but more work needs to be
done to calibrate it for the 0.001 to 0.1 ppm concentrations typically found in use environments. Also, the product is no longer available; any further work will require finding a new
sensitive detector. The housing that was used to isolate and mount the detector should be
adaptable to other materials.
Archivists and librarians can use the data gathered in this project to interpret air quality
measurements made in their photographic storage areas and to guide engineering professionals in the design of new storage facilities. Black-and-white images require very low levels of
airborne contaminants, but the data show that color photographs are more tolerant of longterm exposure to low levels of airborne oxidants. While multiple levels of enclosures (plastic
sleeves, folders, boxes, and closed cabinets) can together mitigate somewhat the attack by
pollutants, archivists should not rely on enclosures for protection against pollutant effects.
Gas phase filtration equipment still has an important role to play in photograph, cinema, and
microfilm storage.
2
Acknowlegments
This research project was sponsored by the Division of Preservation and Access, National Endowment for the Humanities (NEH), by the New York State Program for the Conservation
and Preservation of Library Research Materials, and by Rochester Institute of Technology.
Direct duplicating film and diazo microfiche were provided by University Microfilms, microfilm boxes by Gaylord Brothers, RC print material and processing chemistry by Ilford Photo
Corporation, and color print material by Eastman Kodak Company.
3
Introduction
The grant project Enclosures and Air Pollution in Image Preservation was a three-year research
study that investigated the threat posed by the ingress of polluted air into library and archival
storage environments. This work adds to the knowledge gained in an earlier study, Air Pollution Effects on Library Microforms,2 which dealt with the effects of four common air pollutants
(NO2, O3, SO2, and H2S) on microfilm and other types of photographic materials. Whereas
the original study evaluated the gross sensitivity of photographic materials to pollutant gases,
one of the prime focuses in the current work was to explore in depth those sensitivities at test
conditions more in line with real life.
In the complex situation of a real archives or library, the contribution that air pollution
makes to the fading of images is not easy to measure or observe. The effects are subtle and
occur slowly, blending in with the action of light, heat, humidity, and the inherent stability
(or instability) of each individual type of photograph. We are not able to say what percentage
of the fading of a color print is due to air pollution. We know it causes some fading, but the
thermal fading characteristics of color materials are probably the major factors.
Because of the chemical nature of images (including in that term products commonly used
in still photography, cinema, microforms, and color hard copy output from computers), it is a
reasonable expectation that airborne pollutants would act to destroy them. Color images are
usually comprised of organic dyes, which depend on complex structural arrangements within
the dye molecule to absorb light. Disturb that precise structure at the right spot, and a yellow
dye becomes colorless, or a cyan dye becomes a weak yellow. Black-and-white photographic
images are comprised of metallic silver, which must first become oxidized before it can degrade;
but, with silver, the response to atmospheric oxidants is complex and depends on more than
just the presence of an oxidant.
4
Ozone and Objects Indoors
In recent years, considerable investigation has been done on the effects of atmospheric ozone
on modern and traditional artists’ pigments.3,4,5,6,7 Ozone is a concern because it is such a
strong oxidizing agent, especially reactive toward the double bonds in organic dyes, which
often are part of the key chromophoric (color-generating) groups on dye molecules. The research (much of which was done at an O3 concentration of 0.40 ppm, the approximate peak
outdoor ozone levels in a polluted area) found that colorants vary in susceptibility, and that
some are quite sensitive. A very important determinant of susceptibility to attack was not only
the dye structure itself but also whether or not the dye was protected by a binder material, for
example, gum arabic or linseed oil.
Other related research (much of which resulted from a broad initiative on environmental
effects conducted by the Getty Conservation Institute) attempted to both directly measure
and predict from a model the ozone concentrations that would actually be encountered inside
southern California museums.8,9,10 These studies and others outside the conservation field11 have
found that indoor ozone concentrations can be as much as 70% of outdoor concentrations and
that relatively simple models can predict indoor ozone concentrations.
Leaving aside for the moment any air purification system or internal sources of ozone
such as copiers, the amount of ozone in indoor air will be determined by: (1) outside levels,
(2) the rate at which outdoor air is admitted to the indoor environment, and (3) the area and
nature of surfaces indoors. Ozone is decomposed by reaction with any surface (floors, walls,
etc.) so the ratio of indoor surfaces to the volume of air circulating through the space becomes
important.
Items freely exposed to indoor air in a building could accumulate very large ozone doses
over time. Most images, however, are encased in boxes or other forms of storage enclosure.
Based on this model of the behavior of a building, there are two reasons why ozone damage
would be mitigated inside a storage box. First, the air exchange rate between the inside and
the outside of the box is normally low, so the total accumulated ozone exposure inside would
be less than outside. Second, there is also the chance that ozone that does enter the box would
react with the walls and not the contents.
Ozone as an outdoor air pollutant is most effectively produced when abundant sunlight
acts on nitrogen oxides and hydrocarbons. The latter two are characteristic of areas with lots
of cars in use. Though ozone first came to prominence in southern California, many other
urban and nonurban areas have elevated ozone levels.12 Most locations east of the Mississippi
are subject to peak ozone concentrations of 0.04 ppm to 0.12 ppm.13 Local concentrations
(primarily in or near cities) can be higher. Ozone concentrations in cities rise and fall each day
5
because they are generated largely by the action of sunlight, but Chicago, Washington, and
New York at peak levels have about two-thirds of the 0.33 ppm found in Los Angeles.14
In all this work, the main points are that ozone can exist indoors in concentrations high
enough to cause some colorants to fade and that the effects of ozone are cumulative over
time and serious enough to cause damage with only a few months’ exposure. Moreover, the
effects are directly related to the product of concentration times duration of exposure.10 In
other words, two weeks at 0.40 ppm ozone gives the same result as four weeks at 0.20 ppm
or six days at 1 ppm. However, the basis for this conclusion was work done on unprotected
colorants (colorants without a binder). Binders complicate this simple concentration times
time formula and make extrapolations from high concentration difficult.
6
Sulfur Dioxide and Nitrogen Oxides Indoors
Many of the studies of these acid gases have been devoted to the effects of acid rain on outdoor stone and metal objects.15,16,17,18,19 However, levels of both of these oxides are relatively
high in museums, raising concern about books, paper, and works of fine art. Hackney made
measurements of sulfur dioxide at the National Gallery of Ireland, the Victoria and Albert
Museum, and the Tate Gallery.20 Nitrogen dioxide levels were also measured at the Tate Gallery. Hackney found significant levels of nitrogen dioxide in unconditioned galleries, which
correlated well with the sulfur dioxide measurements. Levels of SO2 were also significant in
all three museums and varied irregularly with weather conditions. Levels fell rapidly after a
rain, although winter weather brought levels up. Grosjean and Hisham similarly found that
indoor levels of sulfur dioxide and nitrogen dioxide in southern California museums were a
significant proportion of the outdoor levels.21,22
Limited studies have been performed on the effects of air pollutants on cellulose, cotton, and paper, but these experiments have concentrated on the acid gases, sulfur dioxide and
nitrogen dioxide.23,24,25,26 Of particular significance to accelerated aging research have been
studies by Havermans on the influences of sulfur dioxide and nitrogen oxides on accelerated
aging of paper.27 Havermans showed that in the presence of sulfur and nitrogen oxides, acid
hydrolysis of the paper was the dominant deterioration mechanism. Buffered paper tended to
perform much better than nonbuffered paper although measureable amounts of nitrates and
sulfates were found only in buffered paper.
7
Enclosures and Air Pollution
Enclosures are a very important aspect of storing photographs. Collection managers cannot
change the nature of photographic materials to make them fade and stain more slowly or to be
more physically robust. Nevertheless, among the things that collection managers can control are
handling practices, environmental conditions, and the choice of storage enclosures. Although
temperature and RH are the primary factors in the survival of images, enclosures and handling
practices are next in importance. Whether for still photography or motion pictures, enclosures
add to the useful life of collections by providing physical protection, by buffering rapid environmental changes, and by being inert, harmless containers during years of storage.
There is no one ideal enclosure design for a particular type of photograph; the handling
patterns, storage environment, use environment, and economic circumstances of every collection are different. Enclosures are always part of a multilevel system where each object has an
individual enclosure, which in turn is matched to a box or folder, which finally is placed in a
third level consisting of shelving or cabinets. Ease and safety in handling and the ability to integrate with the other levels should be designed into the overall system from the beginning.
Photographs are found in many different sizes and types—prints, negatives, transparencies, roll films, and sheet films—and all are physically delicate. Whatever style of design and
construction is used, the most important thing is that the enclosure be able to physically perform the tasks desired of it. For example, motion picture film cans need to be strong enough
to withstand the weight of other cans. Transparencies might need clear enclosures so that they
can be examined without being directly handled.
One other aspect of enclosures is significant: their chemical inertness toward photographs
stored inside them. Enclosures should not emit harmful gases or leach out substances that
would cause dye fading, staining of gelatin, or other problems. The glues, inks, labels, and
coatings used in enclosure manufacture should all be inert and nonreactive with photographs.
There are many examples in real-life collections of damage from inappropriate enclosures and
adhesives; most people are familiar with the stains and residues left by older cellophane tape,
decomposing rubber bands, rusty paper clips, etc. The inertness of photographic storage enclosures can be evaluated by use of the Photographic Activity Test (PAT), an accelerated-aging
method described in ANSI Standard IT9.16-1993, American National Standard for Imaging
Media—Photographic Activity Test. Passage of the PAT is not a guarantee that a storage enclosure
will be satisfactory in all aspects, merely that it will not cause staining or fading of photographs
because of substances emitted by the enclosure.
The protective benefits of enclosures with respect to air pollutants and photographic materials (or other types of archival materials) have not been directly studied using full enclosures
8
with actual materials inside. In recent years, the National Institute of Standards and Technology (NIST) has undertaken research (sponsored by the National Archives) to examine the
issues relating to the microclimate inside a typical acid-free document box. The initial research,
conducted by Elio Passaglia,28 sought to develop a general model for containers that would
predict various aspects of behavior, including how well the document box would insulate its
contents from pollutant gases. Using available information, the model suggested that transport of gases through the box walls was slow and that equilibration would occur principally
through the gaps in the box and would require a few months.28
More recently, new work has been conducted by Dr. Charles Guttman of NIST to actually
measure the rate at which SO2 diffuses through the walls of a typical acid-free document box.
He has found that diffusion through the box wall is substantially faster than earlier estimates,
and now Passaglia’s model predicts that inside/outside SO2 equilibration is complete within
a few days.1
As others have found, the NIST work also shows that the acid-free box wall absorbs SO2
(about 0.2% by weight). NIST’s preliminary data with NO suggests very little absorption, but
NO diffuses through the wall at about the same rate as SO2. Other work by NIST measured
the NO2 diffusion and absorption rates with conventional acid-free and buffered lignin-free
box boards. The NIST research was aimed at refining the Passaglia model by providing more
accurate diffusion rate constants. It did not, however, attempt to measure how much pollutant
enters a box under real-life conditions. The IPI research reported here did involve direct exposures of complete boxes, sleeves, and envelopes and contents to ambient levels of pollutants.
It did not quantify how much of each gas made it through the enclosure, but the resulting
effects on the imaging materials stored inside them were quantified.
9
Figure 1: Layout of IPI Pollution Studies Lab. (A) Computer terminal. (B) Pollution chamber. (C) Gas
monitoring equipment. (D) Cutaway view of free-hanging film samples within pollution chamber. (E) Gas
canisters. (F) Sample preparation area.
Test Apparatus
Figure 1 is a graphic view of the air pollution
testing facility at IPI. This equipment was
acquired with the aid of NEH under a grant
proposal (Air Pollution Effects on Library
Microforms, PS-20273-89) in 1989. The
specially designed incubation chambers are
one of a kind and are designed to withstand
the rigors of constant exposure to varying
levels of corrosive gases and extremes of
temperature and humidity. These chambers
have a large capacity (21 cubic feet) and are Figure 2: Interior view of incubation chamber.
designed to maintain constant temperature,
humidity, and gas concentration while providing recirculation and adequate mixing of the test
atmosphere. Figure 2 shows the inside of one of the incubation chambers. All wetted components of the chamber are constructed of Teflon, polyvinylidene fluoride (PVDF), or stainless
steel. The chamber is depicted without the removable rear panel to show the circulation fans,
heating coil, gas and humidity inlets, sample outlet, and cooling and dehumidification coils.
Test conditions are maintained from a desktop PC that is networked with two ANAFAZE 8
10
Figure 3: Schematic drawing of ozone injection
system used in project.
Figure 4: Exploded view of ozone generator.
loop PID controllers that allow operator input and monitoring of PID function.
The test gases are injected into the chambers from large gas cylinders. NO2, SO2, and H2S
are supplied on demand via the controllers and dedicated Teflon solenoid valves for each gas.
The ozone injection system is outlined in Figure 3. Ozone can be regulated by air volume and
variable output from the PID controller. Ozone is generated on demand using a high-voltage
discharge ozone generator (Figures 3 and 4).
Monitoring of the chamber atmospheres is accomplished by withdrawing a sample from
the chamber outlet and analyzing it with the appropriate gas analyzer. Monitoring equipment
(all manufactured by Monitor Labs) includes the following:
Ozone
Model 8810 U.V. Photometric Ozone Analyzer
Nitrogen dioxide
Model 8840 Chemiluminescent Nitrogen Oxides Analyzer
Sulfur dioxide
Model 8850 Fluorescent SO2 Analyzer
Hydrogen sulfide Model 8850 Fluorescent SO2 Analyzer with Model 8770 H2S Converter
The monitoring equipment is mounted in an instrumentation rack placed between the
two chambers and is calibrated by a Monitor Labs 8500 calibrator. All of the equipment is
interfaced with the controllers and subsequently with the computer.
11
Overview of Test Methodology
This study was divided into three individual phases. In many cases, the phases overlapped each
other and materials used in one phase were also included in one or both of the other phases.
Additional enclosure configurations were added to some tests in order to explore a particular
hypothesis or interest, these will be discussed in the text of individual sections.
The work on the passive ozone monitor encompassed the entire project; these monitors
were added to all incubations. Monitors were also placed in various positions around IPI’s lab,
for instance, over the photocopier, over the laser printer, in the collection storage area, etc., in
an attempt to look at their behavior in as many microenvironments as possible.
The specific differences in each phase of the project are discussed in the overview that
follows.
The experimental plan was divided into the following three phases:
Phase I: Study of Pure Oxidizing Gases at Ambient Conditions
Phase II: Study of Synergistic Effects
Phase III: Study of Enclosures
Development of Passive Ozone Monitor (all test conditions)
Phase I: Study of Pure Oxidizing Gases at Ambient Conditions
In this phase, pure oxidants were run at low concentrations for an extended time period. Only
the pollutants ozone and nitrogen dioxide were studied at the 0.1 ppm (100 parts per billion)
concentration, because the previous study showed that these are the two more aggressive oxidant gases. The tests were run for one year at 25°C, 50% RH. To separate the effects of the
pollutants from normal aging, all samples were also incubated for the same time period in a
humidity-controlled chamber at 25°C, 50% RH without any pollutant gases present.
Specimens were removed from the pollution chamber every four months, measured for
density, and then replaced in the chamber. Samples were suspended in the chamber and freely
exposed to the chamber atmosphere. This approach simplified the specimen preparation, requiring only two specimens of each material type per chamber.
A wide and broadly representative variety of photographic materials were tested. This
maximized the information that could be obtained and was highly desirable in view of the
long incubation times required and limited time blocks available.
1. Negative motion picture film (Kodak 5272). This product showed significant
ozone-induced color fading in the original study, particularly of the yellow dye.
2. Positive motion picture film (Kodak 5384). This proved to be the most ozonesensitive chromogenic film that was evaluated in the first study.
3. Conventional chromogenic color print (Ektacolor). This is a very important mate12
rial of great interest to archives, and it has a fairly high ozone sensitivity.
4. Diazo microfilm (Xidex). This product is an important micrographic film for user
and service copies.
5. Source document microfilm (Fuji HR2). Although silver images did not prove to
be as sensitive as color images to the effects of pure oxidizing agents, they can be prone
to such defects as silver mirroring in the presence of some combinations of pollutant
gases. This is typical of films used as master negatives in preservation microfilming.
6. Source document microfilm, polysulfide treated (Fuji HR2). Polysulfide treatment protects the silver image against oxidants by converting the silver to silver sulfide, which is more peroxide-resistant. Verification of the resistance of sulfided silver
to prolonged exposure to low levels of ozone and nitrogen dioxide and to pollutant
combinations was the purpose for including this material.
7. Direct duplicating microfilm (Kodak 2468). This film is widely used in the microfilm industry. In the original study it showed slightly greater changes than the silver
camera microfilm.
8. Colloidal silver film (detector used in the ANSI Photographic Activity Test).
Although this is not a commercial or user product, colloidal silver has proven to be
much more sensitive to the atmospheric environment and pollutants than filamentary silver images. It is for this reason that colloidal silver is used in the Photographic
Activity Test to evaluate enclosure materials. In the first pollutant program at IPI,
colloidal silver was much more sensitive to the effects of ozone and H2S than silver
camera microfilm.
9. Ilfochrome color micrographic film (Cibachrome CMM). Although this product
is not as widely used as the chromogenic color materials, the dyes are inherently more
stable. It is being used in a number of color preservation microfilming applications.
10.Resin-coated black-and-white paper print (Ilford Polycontrast). There are many
practical examples of these prints showing silver mirroring, fading, or microblemishes
when exposed to pollutant atmospheres. Their inclusion in this study should provide
the archivist with practical information about this important imaging material.
11.Fiber-base black-and-white paper print (Kodak Polyfiber). This is similar to the
previous product, but its paper base can more readily absorb atmospheric pollutants.
12.Thermal dye diffusion print (Kodak Ektatherm). Although this color hard copy
material and similar products from Sony, Tektronix, and Mitsubishi is not yet widely
stored, it likely will be in the future. Consequently, a comparison of the relative stability of some of these newer color hard copies with that of the traditional chromogenic
13
photographic materials is of considerable importance. This comparison is believed to
be more critical in light of results from the first pollution study. The dyes in this material are not protected by a gelatin binder and proved to be very susceptible to ozone
fading. IPI believes also that this material is so extraordinarily sensitive to ozone that it
may be the basis for a practical long-term ozone monitor for libraries and archives.
13.Electrophotographic color print (Canon Color Copier). This product will also
become increasingly important to the archivist. Studies to date have shown it to be
much more stable in the presence of pollutants than the thermal dye diffusion transfer
material.
14.Color inkjet print (Hewlett Packard Paint Jet). This product is also finding application as a printout copy. No information is available on its stability to pollutants.
All black-and-white samples had a step wedge of seven density blocks ranging from Dmin
to Dmax, a range of approximately 0.05 to 2.0 blue density, including 1.0 above Dmin. Color
materials had three sets of color patches (cyan, magenta, and yellow dyes), each color having
four density steps.
Status A blue densities were measured on the seven black-and-white (or neutral tone) materials, while blue, green, and red densities were measured on the seven color images. Density
change and visual inspection for silver mirroring or redox blemish formation were the only
criteria for this phase.
Phase II: Study of Synergistic Effects
The original pollutant program showed that filamentary silver is relatively resistant to the effects
of pure ozone, nitrogen dioxide, and sulfur dioxide. However, there are numerous practical
examples of silver images showing mirroring and/or fading when exposed to an environment
having elevated pollutant levels. It is now believed that this is the result of the interaction of
two or more pollutants. It was considered important to determine if this synergistic effect takes
place under more practical conditions, particularly in the case of NO2 and H2S.
Four pollutant gases were used in this phase in the combinations listed in the table below.
Interactions between the gases were expected, and the increase or mitigation of attack by one
gas in the presence of other gases was the prime concern. Ozone is a strong oxidant, and its
oxidizing effect is greater in the presence of acid. Nitrogen dioxide is also a strong oxidizing
agent; it is strongly acidic as well. Sulfur dioxide is a weak reducing agent and produces acid
in the presence of moisture. Hydrogen sulfide is also a weak reducing agent but is a strong
sulfiding gas. The effects of oxidant combinations were expected to be seen primarily with
color images, while oxidants and sulfur gases were expected to affect primarily silver images.
14
Five gaseous combinations were used in Phase II and are summarized below:
Time Period
Pollutant Concentration
1 year
0.1 ppm NO2 and 0.05 ppm H2S
6 months
0.1 ppm O3 and 0.1 ppm NO2
6 months
0.1 ppm O3 and 0.05 ppm SO2
6 months
0.1 ppm NO2 and 0.05 ppm SO2
6 months
0.1 ppm NO2, 0.1 ppm O3, and 0.05 ppm H2S
The 0.1 ppm concentrations of ozone and nitrogen dioxide are the same as in Phase I.
The 0.05 ppm of hydrogen sulfide and sulfur dioxide are also plausible indoor pollutant levels
for an urban archives. All concentrations are at least a decade higher than the lower detectability level.
Two specimens each of the same fourteen
materials studied in Phase I were studied in Phase
II, using the same density measurements. Densities were determined at intervals of two or four
months, resulting in three sets of determinations for
the six-month studies and three sets for the one-year
study. After each measurement the specimens were
returned to the chamber for further incubation.
All specimens were suspended in the chamber by
stainless steel rods, as shown in Figure 5, so that
they were freely exposed to the pollutants at 25°C,
Figure 5: Diagram of sample-hanging arrangement within pollution chamber.
50% RH.
Phase III: Study of Enclosures
Under practical storage conditions, control of pollutants is frequently impossible because of
the expense of installing and operating the necessary equipment. However, photographic materials are usually placed in enclosures such as sleeves or boxes. It has been shown that these
enclosures will mitigate the effect of pollutants. The unanswered questions were by how much,
and what types of enclosures are to be preferred with each type of photographic material. These
practical considerations were the primary focus of Phase III.
Four photographic materials were chosen for this study:
1. Thermal dye diffusion print (Kodak Ektatherm). This material was selected because
of its very high susceptibility to oxidant pollutants.
2. Positive motion picture film (Kodak 5384). This is a much more common film
which also has high susceptibility to oxidant gases, although not as high as the thermal
15
dye diffusion print material.
3. Direct duplicating microfilm (Kodak 2468). This film is of wide interest in the
microfilm industry where long-term storage is important.
4. Resin-coated black-and-white paper print. This is another example of a widely
stored silver image.
The commonly available enclosures studied were:
1. Buffered paper envelope (Light Impressions Straight Cut Envelopes made from
80-lb. Apollo PaperTM).
2. Nonbuffered paper envelope (Light Impressions Straight Cut Envelopes made from
80-lb. Renaissance PaperTM).
3. Polyethylene sleeve (Print File 35-1M Polyethylene Sleeve).
4. Polypropylene sleeve (Light Impressions 3-mil FoldLockTM Sleeve).
5. Polyester sleeve (Light Impressions 3-mil Mylar D sleeve).
6. Metal-edge box made from lignin-free buffered cardboard (Conservation Resources
Lig-free Type I 35mm Archival Microfilm Boxes).
7. Polyester sleeve inside a metal-edge box (Light Impressions 3-mil Mylar D
sleeve).
8. Buffered paper envelope inside a metal-edge box (Light Impressions Straight Cut
Envelopes made from 80-lb. Apollo PaperTM).
One sample was inserted into each envelope or sleeve. Three replicates of each material
configuration were prepared, one sample for each measurement interval.
The first configuration in this phase was designed to mimic sleeved negatives or prints
that were placed vertically in a drawer. In real life, photographs in this type of configuration
can be placed loosely in the drawer or be packed tightly together.
In this test, in order to limit the number of samples required, a
normal filing cabinet drawer was not used. Samples were instead
prepared to fit into a collapsible 3½″ computer floppy disk storage box. This box allowed the three samples of each material to be
placed in a separate compartment in the box. Placing three samples
in each compartment caused a slight pressure to be placed on the
samples and restricted air flow into the package. This configuration
is seen in Figure 6.
Figure 6: Collapsible floppy
Sleeved prints and negatives are also stored horizontally in disk storage box simulated
boxes where the box itself could act as an impediment to attack
from pollutants in the atmosphere. The second configuration consisted of one sleeved sample placed in a roll microfilm storage box
conditions in a packed filing
cabinet drawer by placing
slight pressure on and restricting air flow around samples.
16
Figure 7: Single sleeved sample in roll
microfilm storage box.
Figure 8: Arrangement of boxed samples in incubation
chamber. Spacing boxes a half-inch apart on raised rack
permitted free flow of air around samples.
(Figure 7). These boxes are not well-sealed. Therefore,
it was presumed that they offered little protection from
ingress of the outside atmosphere, but the extent or lack
of benefit was unknown. Three individual boxes were
required for each sleeve/sample material combination.
The boxed samples were placed on a perforated stainFigure 9: Stack of five sample sheets with- less steel rack at the bottom of the chamber (Figure 8).
out sleeves in roll microfilm storage box.
The rack raised the boxes approximately one inch off the
bottom of the chamber and the perforations allowed air
flow around the samples. A half-inch space was left on all sides of each box to separate it from
its neighbor and allow free air movement.
Another box configuration included in this phase was intended to explore the commonly
seen stack of unsleeved negatives or prints in a box. In this configuration, five separate samples
of each of the four materials were stacked on top of each other and placed in the same roll
microfilm storage box as above (Figure 9). In a normal storage situation there would be many
more objects stacked together—typically whatever the box would hold. This represented a
problem, in that the more objects there are in the box, the more weight and subsequent pressure
there is placed on objects in the stack. Creating large stacks of samples in each box for testing
was impractical, so this configuration included only five samples, and only the top, middle,
and bottom samples were measured. It was felt that, while the heavy stack of materials found
in real life could not be recreated easily, at least the sample-to-sample contact, characteristic of
a stack, could be observed. Three boxes of each sample were prepared for each test.
In conjunction with Phase III, the sleeve permeability test was devised to evaluate a sleeve’s
diffusion resistance or pollutant-trapping capacity (see Figure 10). In this test, 2″ x 2″ pieces
of the thermal print material and the Kodak 2468 direct duplicating film were arranged on a
24″ x 30″ sheet of clear polycarbonate. Each sample was then covered by a 2½″ x 2½″ piece
17
Figure 10: Sleeve permeability test.
of one of the five sleeve materials. There were three separate samples
of each sleeve material for both the thermal print and the 2468 film.
The sleeve materials were affixed to the sheet with aluminized polyester
tape. The samples were thus completely covered and sealed from the
environment. The pollutant gases could affect the samples only by
diffusing through the plastic or paper sleeve material.
Figure 11: Samples were
All samples in Phase III were made as one uniform density patch measured in the five areas
indicated.
of approximately 1.0 density. The single field of 1.0 density was used
to track edge effects, as the gases were expected to penetrate and cause
fading only at the edges of the samples inside the sleeves. Color patches of only cyan dye,
with a density of 1.0 above Dmin, were used for the two color materials. The cyan dye had
previously been shown to be very sensitive to oxidants for both the movie-print film and the
thermal print material. A single patch with a blue density of 1.0 above Dmin was used for the
two black-and-white samples. Measurements were taken at five different positions on each
sample before incubation. A template of clear polyester was used to ensure measurement of
the same areas on each sample. Figure 11 shows the areas that were measured. Since removing
the specimens from the enclosure would disturb the gaseous distribution, it was necessary to
use separate specimens for each time period. Single specimens were prepared and measured
for each time period.
The duration of each test was eight weeks, and there were three sample time periods:
two and one half weeks, five weeks, and eight weeks. Since the primary purpose of this phase
was to determine the relative degree of improvement afforded by the various enclosures, tests
were conducted at 5 ppm of the various pollutants at 25°C, 50% RH. It was recognized that
these conditions were more severe than those found in practice, but longer incubation times at
lower concentrations were not possible within the time allowed. It was felt, based on previous
18
studies, that this concentration would give meaningful changes in shorter time periods and
allow comparisons between enclosures.
Time Period
Pollutant Concentration
8 weeks
5 ppm O3
8 weeks
5 ppm NO2
8 weeks
5 ppm O3 and 5 ppm NO2
8 weeks
5 ppm O3 and 5 ppm H2S
8 weeks
5 ppm NO2 and 5 ppm H2S
8 weeks
5 ppm O3, 5 ppm NO2, and 5 ppm H2S
Note: To obtain a more practical evaluation of the enclosure benefits at lower pollutant
concentration levels, the same eight enclosures were also placed in the chambers for the Phase
I and II studies.
Since the size of the chambers limited the number of metal-edge boxes to 36, time periods
were limited to three for each of the seven atmospheres.
The forty-two separate enclosure configurations are listed on the following page.
19
Polyethylene sleeve/thermal print
Polyethylene sleeve/direct dupe film
GROUP A
Sleeve Permeability
Polyester sleeve/thermal print
Polyester sleeve/direct dupe film
Thermal
print/direct
dupe sealed
under sleeve
materials
Polypropylene sleeve/thermal print
Polypropylene sleeve/direct dupe film
Buffered paper envelope/thermal print
Buffered paper envelope/direct dupe film
Nonbuffered paper envelope/thermal print
Nonbuffered paper envelope/direct dupe film
GROUP B
Sensitive
materials in
buffered,
lignin-free,
metal-edge
boxes
Box/thermal print, stack of 5
Box/color positive film, stack of 5
Box/b&w RC print, stack of 5
Box/direct dupe film, stack of 5
Box/thermal print in buffered paper envelope
Box/color positive film in buffered paper envelope
Box/b&w RC print in buffered paper envelope
Box/direct dupe film in buffered paper envelope
Box/thermal print in polyester sleeve
Box/color positive film in polyester sleeve
Box/b&w RC print in polyester sleeve
Box/direct dupe film in polyester sleeve
Polyethylene sleeve/thermal print
Polyethylene sleeve/color positive fill
Polyethylene sleeve/b&w RC print
Polyethylene sleeve/direct dupe film
Polyester sleeve/thermal print
Polyester sleeve/color positive film
Polyester sleeve/b&w RC print
Polyester sleeve/direct dupe film
GROUP C
Sensitive
materials in
sleeves and
envelopes
Polypropylene sleeve/thermal print
Polypropylene sleeve/color positive film
Polypropylene sleeve/b&w RC print
Polypropylene sleeve/direct dupe film
Buffered paper envelope/thermal print
Buffered paper envelope/color positive film
Buffered paper envelope/b&w RC print
Buffered paper envelope/direct dupe film
Nonbuffered paper envelope/thermal print
Nonbuffered paper envelope/color positive film
Nonbuffered paper envelope/b&w RC print
Nonbuffered paper envelope/direct dupe film
20
How Incubation Conditions Relate to Real Life
The test conditions used in this study were planned with different goals in mind. The shortterm, high-concentration tests were meant to acquire as much data as possible in a short-term
experiment. Relying on data from previous IPI research, we were confident that measurable
density change was possible at the 5-ppm gas concentration in the proposed time frame. In the
long-term tests, the purpose was to simulate as closely as possible real-life exposures. Tables
1 and 2 show a general relationship between real-life concentrations of pollutant gases and
the project test conditions. Table 1 compares the two conditions used in the current study
and shows how long it would take at real-life conditions (assuming an average level of 0.025
ppm) to attain the same exposure received in both of the test conditions. The .025 ppm gas
concentration represents a typical average concentration that might be found in a storage space
that has no filtering or HVAC control. The comparison is hypothetical and based on ozone
only; it assumes a linearity of concentration versus time and does not consider the variability
of the test materials.
According to Table 1, the short-term tests in this project would be equal to approximately
33 years at room conditions. The long-term tests would require about four years at ambient
indoor conditions to reach the test exposure levels.
Table 1: Relationships between test atmospheres and exposure times.
Ozone Concentration
Elapsed Time
(days)
Total Exposure
(ppm hours)
Equivalent Exposure at .025 ppm
(years)
0.05 ppm
6000
7200
33
0.10 ppm*
3000
7200
“
0.50 ppm
600
7200
“
1 ppm
300
7200
“
2 ppm
150
7200
“
5 ppm*
60
7200
“
10 ppm
30
7200
“
* Concentrations used in current study
Table 2: Comparison of the two test atmospheres in the current study.
Ozone
Concentration
Elapsed Time
(days)
Total Exposure (ppm
hours)
Equivalent Exposure
at 0.025 ppm
(years)
0.10 ppm
365
(3000 days would be needed to
equal 5 ppm exposure)
876
4
5 ppm
60
(7.3 days would be equal to 365
days at 0.10 ppm)
7200
33
21
Results
Table 3, on the following page, shows an overview of the sensitivity of each sample material
used in the project to each of the incubation conditions that they were exposed to. Only four
sample materials were used in the short-term experiments, so data is seen for only those four
materials in incubations H through M. The legend for the table lists the test atmosphere and
duration for each incubation and provides a key for the various levels of attack and any other
manifestations of the exposure.
The table shows that the filamentary silver film materials were only slightly affected by these
gaseous atmospheres. In the real world, examples of filamentary silver fading are everywhere,
but this project’s use of plausible real-life storage atmospheres failed to produce much effect in
the time allowed. The mixed-gas incubations sought to mimic the oxidation/reduction cycle
that is known to be the mechanism of silver image fading, but they did not reproduce real-life
fading. The one variable that was not equivalent to real life was time. As noted above, the
low-concentration incubations would only approximate four or five years’ exposure to real-life
conditions. Nevertheless, silver mirroring and redox blemish formation in only a year’s time
at room temperatures and ambient gas concentrations have been observed in the IPI lab.
22
Table 3: Relative sensitivity of the sample materials to test conditions.
A
B
C
D
E
F
G
H
I
J
K
L
M
N
5272
0
0
0
0
0
0
0
5384
0
0
0
0
0
0
0
Ektacolor
0BS
2-
0BS
0BS
0
0BS
0BS
0
Xidex
2-BS
2-
1-BS
2-BS
2-
2-BS
2-BS
0
HR2
0
0
0
0
0
0
0
0
HR2 Toned
0
0
0
0
0
0
0
0
2468
RB
0
0
RB
0
0
0
Colloidal
silver
2+
2-
2+
1+
1-
1+
1+
0
CMM
0
0
0
0
0
0
0
0
0BS/M
0
0BS
0BS/M
0
0BS
0BS
B&W
Fiberbased
0BS
0
0BS
0BS
0
0BS
0BS
Ektatherm
4-BS/CBS
4-
0
0
0
0
0
0
0
0
1-BS
3-
2-BS
2-BS
3-
1-BS
1-BS
0
Material
B&W RC
Electrophotographic
Ink jet
3-BS/CBS 4-BS/CBS
4- 2-BS/CBS 2-BS/CBS
Legend for Gas Atmospheres
Gas Concentration
A
0.1 ppm NO2
B
0.1 ppm O3
C
0.1 ppm NO2 and 0.05 ppm H2S
D
0.1 ppm O3 and 0.1 ppm NO2
E
0.1 ppm O3 and 0.05 ppm SO2
F
0.1 ppm NO2 and 0.05 ppm SO2
G
0.1 ppm NO2, 0.1 ppm O3, and 0.05 ppm H2S
H
5 ppm NO2
I
5 ppm O3
J
5 ppm NO2 and 5 ppm O3
K
5 ppm NO2 and 5 ppm H2S
L
5 ppm NO2, 5 ppm O3, and 5 ppm H2S
M
5 ppm O3 and 5 ppm H2S
N
Control (no gas)
0
1-BS/CBS
RB
0M/BS
0
0BS/CBS
0
0
M/BS
0BS
1+BS/CBS
0BS/CBS
0
0
0BS
0BS
0
0
0
0
0
0
0
4-BS/CBS
Test Duration
1 year
1 year
1 year
6 months
6 months
6 months
6 months
8 weeks
8 weeks
8 weeks
8 weeks
8 weeks
8 weeks
1 year
4-
4-BS/CBS
4-BS/CBS
4-BS/CBS 3-BS/CBS
Level of Attack
0 = No density loss (-) or gain (+)
1 = Slight density loss (-) or gain (+)
2 = Moderate density loss (-) or gain (+)
3 = Severe density loss (-) or gain (+)
4 = Very severe density loss (-) or gain (+)
RB = Redox blemishes
M = Mirroring
DY = Dmin yellowing
BS = Base stain
CBS = Color balance shift
23
0
Phase I: Study of Pure Oxidizing Gases at Ambient Conditions
These two one-year incubations were designed to explore the long-term effects of the oxidant
gases nitrogen dioxide and ozone on the photographic materials in the study. The gases were
used individually in separate chambers at the 0.1 ppm concentration level at 25°C and 50% RH
for a period of one year. These incubations represent a total pollutant exposure approximately
equal to four years in a normal collection environment, assuming a yearly average of 0.025 ppm
of either of the gases. The ventilation air that comes into the collection environment may have
passed through a multiple-bed chemical filtration system that removes a high percentage of
some pollutant gases, or else it may have come in through open windows, causing the indoor
air to closely track the outdoor pollutant levels. The actual level of oxidizing contaminants in
collection environments can vary greatly, but 0.025 ppm is a reasonable figure to represent
real-life average concentrations for O3 and NO2. The currently recommended levels of pollutant gases for museums are very low (<0.001 ppm).12 At these levels, our test atmospheres
represent a 100-year exposure, but the reality is that these levels are lower than can be accurately measured by most instrumentation. In other words, it is not possible to measure such
low concentrations, and the equipment needed to even come close is very expensive and not
practical for most institutions. Given this fact, the purpose of this study was to look at how
dangerous the ambient real-life levels of oxidizing pollutants are and to determine the urgency
of control measures for photographic storage areas.
The fourteen different free-hanging photographic materials used in this test series are
listed in Introduction, Phase I: Study of Pure Oxidizing Gases. (“Free-hanging” means that
materials were not in enclosures; they hung freely in the chamber.) Descriptions of their importance and of the sample preparation and measurement are found there. The four “sensitive”
materials used in Phase III (see Phase III: Study of Enclosures), in their respective enclosure
configurations, were also included in this phase.
According to the data from this study, most of the common photographic materials tested
would not show any effect from ambient levels of oxidizing pollutants for many decades. The
exceptions were those color output materials that deposit their imaging material directly on
the support surface with no binder layer or surface lamination to protect it. These exceptions
included thermal diffusion print material and ink-jet prints. Also included in the materials
sensitive to oxidation were the Xidex diazo microfiche and the colloidal silver indicator strip.
Both of these materials were also badly oxidized in previous IPI research using much higher
concentrations of gas and higher temperatures and humidities. The significance here is that
even at low concentrations and room temperature and humidity these materials will likely
display substantial fading within a decade. While the colloidal silver is not found in modern
24
photographic products, it is similar to many 19th-century print materials. The results with colloidal silver show that the size of the silver particle is directly related to its oxidation potential.
The colloidal silver material, which has very small silver particles, was moderately affected by
long-term exposure to both 0.1 ppm O3 and 0.1 ppm NO2. On the other hand, some of the
silver materials in the study with longer, filamentary silver particles were not faded by the pure
oxidizing gases. However, the RC prints and the duplicate negative material formed either
silver mirroring or redox blemishes, indicating that they were affected by low-level NO2.
0.1 ppm Ozone
Pure ozone, one of the strongest oxidizing gases present in polluted air, actually had little effect
on those materials that carry their final imaging materials in a gelatin binder layer. At 50%
RH, this layer of hardened gelatin impedes the diffusion of the ozone enough to protect the
silver or dyes of the image. While the unprotected dye images (the thermal diffusion and inkjet prints) were readily faded in the low-concentration ozone atmospheres, none of the silver
materials (with the exception of colloidal silver) demonstrated any adverse effects.
Color
Both the thermal and ink-jet prints lost 40% to 50% of their original density in all dye sets over
the one-year test period. As expected, none of the samples had a color shift or Dmin staining
or yellowing. Ozone tends to bleach the supports along with fading the dyes. Although the
thermal and ink-jet prints were severely faded by ozone, other research has demonstrated2
that the thermal and light sensitivity of these products is so high that if they are not placed
in cool, dark storage they will fade substantially in just a few years. If they are placed in the
proper storage environment, the effect of ozone would be minimized in relation to the storage
temperature as ozone attack is temperature dependent also. All of the other color materials
were unaffected by low concentrations of ozone.
Black-and-White Photographic Materials
None of the silver photographic products tested (except for colloidal silver, which has extraordinarily small image particles) showed any effect of low-level ozone exposure. Unlike
the pure nitrogen dioxide and mixed nitrogen dioxide incubations, there was no formation of
silver mirroring or redox blemishes in the silver prints or films. The likely explanation for this
is the lack of any reducing source in the atmosphere. It can be hypothesized that without a
reducing agent present the silver particles form an area of ionic silver around themselves that
acts to retard further silver oxidation. If there is no “event” to disrupt the equilibrium, that is,
no introduction of a reducing agent or transportation of the ionic silver away from the silver
25
particle by increased humidity or temperature, oxidation cannot move forward. The real-world
mechanism of the silver oxidation-reduction cycle, while understood in a theoretical sense, has
not been reliably reproduced in our laboratory tests.
The only “black-and-white” material to have a density change when exposed to pure
ozone was the diazo microfiche, which is a non-silver product. As seen in the description of this
material (item 4 in the materials list) the image is made of dyes created by the light sensitivity
of diazonium salts that are dispersed in a polymeric binder. These resulting dyes are sensitive
to oxidation by ozone, and this process is very temperature-dependent. Higher temperatures
will increase the rate of fading and cause discoloration of the base material by dispersion of
the dyes. There was no base discoloration in these ambient temperature and humidity tests,
but the higher-density areas of the samples lost about 10% of their beginning density during
the one-year test period.
0.1 ppm Nitrogen Dioxide
Another important oxidizing air pollutant is nitrogen dioxide. This gas is produced by combustion at high temperatures and is characteristic of urban air pollution. Like ozone, it has
been identified as a threat to the double bonds of organic dyestuffs. NO2 is a concern because,
unlike ozone, it does not readily decompose on indoor surfaces, and it is difficult to control
with current air purification systems. Without filtration, concentrations of NO2 indoors closely
track those found outdoors.
Color
The most important findings in the NO2 incubation were the discolorations and color balance
shifts in some of the color samples. Most notable was the change in the thermal print material,
which not only lost image density but also went through a marked color shift. Figure 12 depicts
the effects on the thermal print material of pure nitrogen dioxide (center graph) compared with
those of pure ozone on the left and a mixture of ozone and nitrogen dioxide on the right. This
graph is based on data from the 5-ppm tests, but the one-year data are similar (there was no
mixed-gas incubation in the one-year tests). It can be seen that all of these incubations severely
faded the cyan dye of the samples but that the fading was worse with the pure nitrogen dioxide
than with pure ozone or a combination of ozone and nitrogen dioxide. Green and blue densities of the cyan dye increased with the pure nitrogen dioxide as compared to the decrease with
pure ozone and slight blue density increase with the gas mixture. This made the original cyan
dye turn a muddy pink color in the pure nitrogen dioxide samples, become lighter and lighter
in pure ozone, and display a slight magenta cast in the mixture. The yellow and magenta dyes
also had a slight color shift along with an overall fading of both these dyes.
26
Figure 12: Comparison
of NO2 , O3 , and O3 /
NO2 combination. Concentration: 5 ppm. Total
exposure: 56 days.
In contrast to the rapid fading of the thermal print material and the ink-jet prints, the
free-hanging color films in this incubation had no density loss throughout the test period.
There was a blue density increase in the color positive motion picture film (Kodak 5384) and
in the Ilfochrome samples. The color positive film gained about 15% blue density in the yellow dye patch while the Ilfochrome gained approximately 10%. This is the result of yellowing
induced by the NO2. The color negative film (Kodak 5272) was unaffected in this atmosphere.
Color positive film used in the enclosures neither lost density nor gained blue density as did
the free-hanging samples.
Of the four color hard copy samples, only the thermal print material and the ink-jet print
material showed any marked density loss or color shift. The chromogenic color print (Kodak
2001) was not affected by the nitrogen dioxide atmosphere.
Base Staining of Print Supports
In all of the incubations where nitrogen dioxide was used, many of the papers and print supports
were stained to varying degrees. Generally, there was a progression of staining from the edges to
the center even in the sleeve samples that were open on only two sides. In contrast, the fading
of the dyes in the ozone incubation progressed from the top and bottom to the center, often
with the two sides of the sample being the last areas to fade. The thermal print material was
once again the worst affected. In fact, the buffered paper sleeves housing the thermal samples
were stained to a greater degree than those that contained the RC prints. Apparently the thermal
print support acted as a reservoir of absorbed gas; the gas was subsequently absorbed by the
paper sleeve. This combination of nitrogen dioxide and the thermal print was the only case in
which the buffered paper was stained. The NO2 staining was present in all of the mixed-gas
experiments that used NO2 as one of the component gases, but the staining was somewhat
27
less as a result of the other gas/gases present. The RC print support was similarly stained in
the high-concentration NO2 incubations, but it did not exhibit the same level of staining in
the low-concentration tests. Free-hanging samples of the electrophotographic, chromogenic
color print, and ink-jet print materials were not stained by the low-concentration NO2 atmospheres but were not tested in the high-concentration incubations. It has been observed in
other research that many paper-based materials exposed to nitrogen dioxide acquire a yellow
stain to some extent.27 Such staining is especially severe when a reaction occurs between the
nitrogen dioxide and lignin in the paper. However, this does not explain the staining of the
thermal print support which, presumably, is a high alpha-cellulose support that should not
have a high lignin content.
Staining of Plastic Enclosures
One other notable aspect of the nitrogen dioxide exposures was the yellow staining of the
polypropylene sleeve material. A measurable blue-density increase of this material was noted
in all NO2 incubations. None of the other plastics displayed any yellowing or physical effects
due to the exposure to the pollutant gases except for a measurable Dmin density increase in
the Xidex diazo microfiche. It is unclear whether this was a reaction with the support or the
polymer emulsion of this product.
Black-and-White Photographic Materials
Only the colloidal silver indicator strip and the Xidex diazo microfiche, among the free-hanging
samples, were affected by nitrogen dioxide. None of the free-hanging filamentary silver materials showed any change in density or base staining in the low-concentration tests. It was
only in the sleeve configurations that any change in filamentary silver materials was noted. In
the computer disc storage box, many of the duplicate negative (Kodak 2468) film samples
developed redox blemishes along the bottom edge of the sample where there was limited air
flow through the package (see Figure 13). The RC print material developed a band of silver
mirroring and red stain in the same area (see Figure 14). The areas of the samples that were
more exposed to the air flow in the chambers were not affected. There were no visible effects
on any of the filamentary silver materials in any of the other enclosure configurations (inside
the microfilm boxes or sealed under the sleeve material in the permeability test).
The diazo film faded much more in the nitrogen dioxide atmosphere than it did in the
pure ozone atmosphere. It was also severely stained. Blue density gains of 0.30 from a beginning density of 0.12 were seen in the Dmin and low-density areas while the high-density areas
lost 20% to 30% of their starting density. It is not clear what percentage of the blue density
increase was caused by yellowing of the polymeric binder and support of this product. Dispersion of the diazo dyes is probably responsible for some of the increase.
28
Figure 13: Red spots (redox blemishes) along bottom
edge of sleeved film sample stored in disc storage box
and exposed to nitrogen dioxide.
Figure 14: Band of silver mirroring and red stain
along bottom edge of RC print material.
A substantial blue density increase was noted in the colloidal silver samples. Again it is
unclear whether this can be interpreted solely as reduction of ionic silver or staining of the
emulsion and the film support. In incubations using sulfiding gases, density increases are
probably caused by reduction of the silver alone, but with nitrogen dioxide it is not possible
to separate the two phenomena.
29
Phase II: Study of Synergistic Effects
Modern urban smog is a dynamic substance that is constantly fluctuating, its concentrations
of constituent gases changed by influences such as temperature, humidity, light, and source
emissions. These gases work upon one another in a number of different ways. They can act to
neutralize each other or mix together to create new species that are more potent than either
of the parent species. How these phenomena affect collections is the thrust of the mixed-gas
incubations. Some gas mixtures might be expected to push forward a mechanism such as silver
image deterioration (oxidation/reduction), or to become more aggressive (combined oxidants).
This work did not include the fluctuations in temperature and humidity that are a part of the
everyday cycle of the mixing of the atmosphere but only sought to outline the relative changes
that occur when other chemical components are added to the pure gases in the incubations.
The results are interesting and sometimes confusing.
The five gaseous combinations used in this phase of the project and the reasons for including them are outlined in Phase II: Study of Synergistic Effects. All of these incubations utilized
low (near ambient) levels of gases and long incubation times (six months to one year). While
these incubations represent an equivalent exposure of only about two to four years at normal
everyday conditions, it was felt that useful data could be gathered in this time frame. Longer
incubations, while preferable, were not possible because of the limited project duration.
Oxidizing/Reducing Gas Mixtures
The primary aim of this series of tests was to explore and recreate the oxidation/reduction cycle
that is the mechanism of silver image deterioration. In previous IPI research, pure gases at high
concentrations and elevated temperatures and humidities failed to affect the filamentary silver
images.2 The current work also revealed few of the anticipated effects on silver images.
Effects of 0.1 ppm NO2 /0.05 ppm SO2 , 0.1 ppm O3 /0.05 ppm SO2 , and 0.1 ppm NO2 /0.05 ppm
H2S
Color Materials
The thermal and ink-jet prints were the only color samples that were affected in these incubations. They were faded by all atmospheres but to a lesser extent than by either of the pure
oxidizing gases by themselves. A color shift like the one resulting from the pure nitrogen dioxide incubation occurred in the NO2 /SO2 atmosphere, but it was not as marked. It was also
seen in previous research that SO2 by itself had no impact on the fading of color images even
at high temperatures and high gas concentrations.2 It has been shown that samples of paper
deteriorate more readily when exposed to NO2 /SO2 than when exposed to NO2 alone,27 but
these studies used a high-temperature post-incubation to increase the reaction rates. Because
30
the thermal and ink-jet prints showed less fading in these mixed-gas incubations, it is assumed
that the oxidizing and reducing gases partially reacted in the chamber atmosphere before any
absorption by the samples could take place. This reaction would effectively reduce the amount
of gas in the chamber and subsequently lessen the total amount of fading of the samples. Also,
at the low relative humidities used in this study, it is doubtful that any absorbed acidic gases
would have much effect until the moisture content of the sample was increased, thereby causing
a more receptive environment for the formation of the reactive by-products of these gases.
Black-and-White Silver Materials
The only effect observed in any of the silver materials was a slight density increase in the colloidal silver detector. This might be explained first by the exposure time being half as long as
that of the pure NO2 incubation, and second by the same argument that was used with the color
materials above. If the gases had a partial interaction in the free atmosphere of the chamber
before they were absorbed by the samples, the effective concentration of the individual gases
would be less than in those incubations using pure gases.
Oxidant Gas Mixtures
Effects of 0.1 ppm O3 /0.1 ppm NO2 (Six Months)
These two oxidant gases occur together naturally in the atmosphere, but their peak levels
never occur at the same time during the day. Generally, ozone peaks in the early afternoon,
and nitrogen dioxide peaks late at night. Because of this, this study is somewhat unrealistic,
but it may be indicative of what is going on during the transitional periods between peaks of
the individual gases. In the high-concentration tests, this combination was most aggressive
towards the silver samples, causing severe silver mirroring across the top edge of the RC-sleeved
samples in the computer disc storage box.
Color Materials
Although the thermal and ink-jet prints were severely faded, the total amount of fading was
not as extensive as that noted in the pure NO2 incubation. This incubation, while effectively
having double the gas concentration of the pure NO2 and O3 tests, was only half as long.
As noted earlier in this report, this gas mixture, while not as aggressive as pure NO2, did
produce more fading in the color samples and more silver image changes than pure O3. This
increased activity with silver images probably indicates the decomposition of some of the O3
by interaction with the NO2 but also suggests a higher level of oxidation/reduction as a result
of combining the two gases.
None of the other color materials were affected by this test atmosphere owing to the shorter
test period and to the gas interactions. The yellow density increase in the color positive film
31
was much less in this incubation. Furthermore, the Dmin staining of the thermal support that
was so severe in the pure NO2 incubation was substantially less in this mixed-oxidant test.
Black-and-White Silver Materials
The amount of blue density increase in the colloidal silver detector was less than in the pure
NO2 test, but the density did not decrease as it did in the pure O3 test. The RC print samples
in the sleeved configurations had random occurrences of silver mirroring and red discoloration.
There seems to be no pattern to the attack on the RC prints; some samples were mirrored at
the first inspection time, and some showed no mirroring at all. The free-hanging silver samples
were not affected in this incubation, and none of the RC samples contained in the microfilm
storage box configurations showed any mirroring or discoloration. It was only on the sleeved
samples in the computer disc box, and then only on the bottom edge of the sample, that the
mirroring was present. Apparently the diminished air movement at the bottom of this box
creates an environment that favors migration of the ionic silver to the print surface where it
is reduced at the uppermost edge of the emulsion, thus forming the silver mirror appearance.
The samples in microfilm boxes did not mirror, possibly indicating that there was enough
interaction between the gas mixture and the box walls to slow the process by allowing too
little time for the formation of silver mirroring. The direct duplicating film did not form redox
blemishes in this incubation.
Effects of 0.1 ppm NO2 /0.1 ppm O3 /0.05 ppm H2S (6 Months)
This combination of gases included three of the four constituent gases of modern urban smog.
In real life, these gases would appear in varying proportions, and certain gases would have
daily peaks that are not reflected in this study. Recreating the typical daily cycle of smog in Los
Angeles would be impossible. It was felt that this combination of gases would be the most
active of any in the project; however, although the combination of NO2 and O3 (discussed
above) did cause slight silver mirroring in some of the RC print materials, it did not cause as
much fading of the color samples as the pure NO2 incubation. The addition of H2S to this
mixture made it less effective both in causing silver image changes and in fading the dyes of
the color materials.
The combinations of gases in this study that logically should have been most detrimental
to silver or to dyes were the most benign, and vice versa. Perhaps such results only reflect the
short-term outcome of gas mixtures. It is also possible that given more time, or else with a
change in one of the other variables (such as an increase in temperature or humidity during a
portion of the day), these combinations would prove to have effects more in line with what
might be expected from them.
32
Color Materials in Mixed NO2/O3/H2S Atmosphere
As in many of the other experimental atmospheres, the thermal and ink-jet prints were the
only color materials that displayed any fading or color shift in the mixed-gas atmospheres. The
extent of fading, though severe, was considerably less than that in the NO2/O3 test, which, in
turn, was less than that in the pure NO2 atmosphere. Figure 15 shows the reduction in the
amount of fading of the pure cyan dye of the thermal print material in these three atmospheres.
It is clear that the test atmospheres were less potent when mixed gases were used, but this test
series did not explore the longer-term effects of absorbed chemical compounds that remain in
the sample materials. There were no measurements of acidity change or any chemical analysis
of the materials after incubation. Further exploration of these questions is needed.
Figure 15: Comparison of cyan density loss of thermal print in different oxidizing atmospheres.
33
Phase III: Study of Enclosures
Because the thermal print was the most sensitive material in the tests it also became the best
gauge of the relative protection offered by the enclosures. Any discussion of effects will generally be in reference to the thermal samples.
Paper and Plastic Sleeves
All of the sleeves in the study, although of slightly different sizes, were of the same basic configuration. Some of the sleeves were used as they were received from the manufacturer: that is,
they did not need to be reconfigured. The polyester and polypropylene materials were made in
the L-fold self-lock style that was adopted for the project. This style allowed the atmosphere to
diffuse into the package through the top or bottom openings of the sleeve. The polyethylene
sleeves were originally pocket-style enclosures meant to accept 3¼″ x 4¼″ negatives; these
were trimmed on the bottom edge to the dimensions of the sample, thus opening up the sealed
bottom edge to conform to the other sleeves. Both of the paper sleeves were adapted to the
project by either folding or trimming to fit. The buffered paper sleeve was originally an 8″
x 10″ negative envelope which was cut down and folded into the L-fold configuration. The
nonbuffered material was originally meant to house a 2¼″ negative strip and needed only to
be trimmed to the correct length. It would have been interesting to look at many other types
of sleeve, but space limited the project to the L-fold configuration.
Figure 16 graphically demonstrates that plastic-sleeve configurations that are open on
two ends, regardless of the material of manufacture, offer little protection against pollutant
gases and serve more as barriers against physical damage.
The polyester-sleeved sample
lost over 60% of its starting
density (beginning density of
1.0 above Dmin) during the
eight-week test period. This
is comparable to the paper
sleeves and the free-hanging samples. Plastic-sleeved
samples in the computer disc
storage box, where there was
slight pressure on each group
Figure 16: Comparison of density loss in thermal print samples in differ- of three samples, displayed a
ent enclosure configurations when exposed to nitrogen dioxide.
reduced level of fading in the
34
central area of the sample where the plastic of the sleeve was in intimate
contact with the material. This behavior would seem to indicate that a
slight pressure on a stack of sleeved prints would be beneficial. However,
this could cause problems in photographs that were already starting to
degrade or those that were exposed to a high-humidity environment. In
such a case, added pressure and intimate contact with the plastic could
cause blocking or ferrotyping. Also, with actively degrading acetate or
nitrate films, this type of storage could impede the release of acid vapors
from the film which would accelerate acid-induced hydrolysis. Both of
these scenarios often have been encountered in real collections.
There is a noticeable progression of attack from the open edges
inward on samples in the plastic sleeves (see Figure 17), but ultimately,
the samples were faded overall. It is interesting that in real life the fading Figure 17: Typical fadof black-and-white images is typically from the edges in to the center. ing pattern in plastic
sleeves
Local fading often follows the outlines of where an image was exposed
to the atmosphere either by being partially covered by another object on top of it or by being
incompletely protected by a sleeve. This localized fading behavior is almost unknown in color
photographs, where fading is nearly always uniform across the entire image. Furthermore, every
image in a batch is usually faded to a similar degree. This means that the inherent instability
of the dyes, not atmospheric attack, is the cause of most of the fading. In this study, where the
levels of pollutant gases were artificially high, the two color materials did exhibit this localized
fading, but at an exposure equivalent to over 30 years at real-time levels. In that same 30-year
period at 25°C and 50% RH, the thermally induced fading of the object would approach the
same or perhaps a higher level and would probably mask any pollutant damage.
In the paper sleeve products, fading proceeded at a fairly even rate at all points on the
samples; neither the buffered nor the nonbuffered papers impeded the diffusion of the gases
through the sleeve. In fact, this research indicates that the alkaline buffering in paper does not
protect the object stored inside it from ingress of contaminated outside atmospheres. What
benefit it may provide is in protecting the paper of the sleeve itself from acids in the air or
those produced by decaying materials in contact with it.
By the end of each of the eight-week test periods, all thermal samples in all of the opensleeve configurations were severely faded. The effect on some specific materials was different
with individual gases, but this occurred in both the free-hanging and sleeved configurations
and will be discussed in context with the individual gases.
35
Paper and Plastic Sleeve
Permeability
The purpose of these tests was
to explore the amount of protection each of the sleeve materials offered when sealed at the
edges against the atmosphere,
allowing the pollutant to enter
only by diffusion through the
paper or plastic.
The results of these tests
revealed that all of the plastic materials offered almost
complete protection against Figure 18: Cyan density loss in thermal print samples sealed under five
different sleeve materials.
pollutant attack. The comparative fading of the different plastics was very similar in all the tests. It should be noted that this
type of configuration (encapsulation), while offering complete protection against the outside
atmosphere, seals any deterioration by-products in the package. These by-products can then
interact with the encapsulated object. This would be especially problematic with degrading
nitrate or acetate film base that is actively releasing acids as part of the deterioration process.
Paper sleeves demonstrated no mitigating effect on the diffusion of the pollutant gases
into the sample package. In all the tests, samples were faded at the same rate and to the same
ultimate level as those samples with no protection. It was thought that buffered paper would
display some capacity to react with the gases and slow down the rate of fading. The data show
that buffered paper offered no additional protection against these pollutant gases even in the
low-concentration (0.1 ppm) tests. Figure 18 illustrates the varying degrees of protection offered by the five sleeve materials.
Multiple Layers of Sample Material in a Microfilm Storage Box
This configuration was designed to mimic many real-life situations where photographic materials are stacked in storage boxes. In reality, there could be hundreds of prints or negatives
stacked in one box, but the logistics of trying to track so many different samples was impractical. It was decided that five samples were enough to model any protective effect offered by
the stack. The typical progression of attack on the five stacked samples is pictured in Figure
19. In this example, the progression of yellow staining of the color positive film caused by
nitrogen dioxide is easily distinguished by the dark discoloration starting at the edges and
36
moving toward the center. Only the top, middle, and bottom samples
were measured for density loss.
The results of these tests indicated that stacking materials on top
of each other offered protection to the extent that there was intimate
contact between the sample observed and the ones directly adjacent to
it. Any air space between the individual objects allowed the pollutant
gases free access. The appearance of the samples after incubation closely
replicated that of black-and-white prints and negatives found in real-life
storage. Quite often we find that prints stored in this manner will have
silver mirroring or fading on the edges or will display a very definite line
of mirroring around an area that was masked by another print. With
color photographs, previously mentioned, fading due to the inherent
instability of the dyes overtakes the slower, pollution-induced fading.
For this reason, overall rather than localized fading is seen in real-life
storage situations with color photos. Nevertheless, the current work
shows clearly that ozone and nitrogen dioxide can indeed cause fading
of chromogenic color dyes as demonstrated by the substantial fading of
the color materials at 5 ppm of the oxidizing gases. Thus, it appears that
in most real-life circumstances, oxidizing air pollutants do not present
a major threat to color collections because of several mitigating factors.
The typical outdoor average concentrations of oxidizing gases, even in
urban areas, are not high enough to cause major fading. The inherent
sensitivity of chromogenic materials to oxidants is not particularly high,
compared to that of some other kinds of dyes, and the gelatin emulsion
protects the dyes to some extent. Together, these facts mean that an
unusually high concentration of oxidant would have to be present for a
considerable period of time in order to cause serious dye fading.
The rate of fading of the exposed areas within the stacks is analogous
to that of unprotected samples in the same atmosphere and indicates little
real protection by the buffered board of the box. Other IPI research has Figure 19: Typical proshown that close-fitting metal or plastic containers substantially buffer gression of attack on
stacked samples.
the microenvironment of roll films against fluctuating humidity levels; it
can be assumed that they would also reduce the exposure to atmospheric pollutants.29 However,
the same research also pointed out that by trapping deterioration by-products in the package
with no means of escape such close-fitting containers could be detrimental and actually could
fuel the autocatalytic deterioration process.
37
Passive Ozone Monitor
Development of the proposed passive ozone monitor was based on the use of Kodak Ektatherm
Dye Diffusion Transfer print material because of its sensitivity to atmospheric oxidants, as
observed in previous IPI research.2 This sensitivity was reconfirmed by the results of the current project. The process of image formation in this material makes the resulting image more
susceptible to attack from the atmosphere. Whereas in chromogenic color prints the imaging
dyes are suspended in the gelatin emulsion, the thermal print image resides on the surface (it
is not absorbed into the print fibers or dispersed in an emulsion) and is more immediately
exposed to the changes in atmospheric conditions. With its imaging dyes so readily accessible
and so sensitive to oxidants in the surrounding air, this material made an excellent detector of
high levels of oxidizing contaminants in the storage environment. In addition to having the
required “high sensitivity,” a small patch of this material is relatively inexpensive and, because
the prints are generated by computer, easily produced. On the downside of its high sensitivity,
this material was also very easily faded by the action of light and high temperatures. This made
it necessary to shield the detector from direct exposure to light. Other concerns in developing
the monitor included (1) allowing for adequate air diffusion to the detector while shielding it
from light, (2) arriving at a simple mounting system, and (3) developing a method for evaluating color and density changes over time. Given these criteria, the results of this research are
described below.
Choosing a Housing
Clearly, making an inexpensive monitoring device precluded the expense of a custom-made
housing for it. Therefore, a search was undertaken for an existing housing that would both
permit air diffusion and block light. There are many products on the market that are made
to measure various components of the atmosphere. Most of these are large, very expensive
monitors for specific gases using chemiluminescence detecting technology. There are personal
dose badges, also specific to individual gases, that require laboratory chemical analysis to determine concentration. The badges are relatively inexpensive, but the lab analysis is costly. It
was determined that the existing technology was inappropriate and that a new approach was
needed. After exploring many ideas, it was decided to adapt a filter cartridge housing of the
type used on respirator masks. These are two-piece holders that are meant to house a variety
of organic vapor, acidic gas, and particulate filters. This housing’s louvered front allows for
plenty of air diffusion into the compartment but blocks most of the light. The housing and
other components of the monitor are pictured in Figure 20. There is a tab on the front cover
of this housing that was meant to ease separation of the two halves of the unit. By drilling a
38
small hole in this tab it was possible to mount
the housing on the wall with a nail or screw or
to suspend it from a string. It is also possible
to lay it on a flat surface.
The Detector
Detectors were made from the same 100%
cyan dye prints used for the Phase III enclosure samples. For this project, the detector was
simply cut out of full sheets of the processed
Figure 20: Components of the passive ozone monitor.
thermal print material. The disks were cut
to a diameter of 3½″, the inside dimensions of the filter housing. Although a strictly visual
evaluation of the monitor was planned, density measurements were taken from five different
areas of the sample for these tests. This allowed pinpointing any areas of uneven fading caused
by the air-flow characteristics of the housing that would not have been readily noticeable in
visual inspection. It also allowed a direct comparison with the other samples in the tests. The
density of these patches was approximately 1.0 above Dmin.
These detectors were deployed in all incubations of the project. Samples of the detectors,
in their housings, were also placed in several different areas of the IPI laboratory. Concentration levels of the lab environment were not monitored but were assumed to be average for our
geographical area. Placement of a portion of the detectors was meant to isolate “hot spots”
in the lab, e.g., above the laser printer, in close proximity to the copier, etc. Light levels in
these areas fluctuated according to the use of the particular space but were generally similar
to a working collection storage space, where lights may be on from 10 to 12 hours daily. In
the incubation chambers, light was necessarily excluded, but the samples were placed in their
housings for uniformity of result. Two different samples were prepared to test the effect of
the room lighting. One half of one of the housings was opened up by cutting the louvers out
of that section to allow unimpeded light to reach one half of the enclosed sample but not the
other. Another sample was placed on a flat surface, fully exposed to available room light. These
samples were measured on the same schedule as the other lab specimens.
Those detectors that were included in the test incubations were pulled and measured on
the same schedule as the other samples in each test. There were only two detectors placed
in each incubation, and both were pulled at each measurement period, measured, and then
returned to the chamber. The samples that were distributed in the IPI lab were dismounted
periodically and evaluated. These samples have remained in place since the beginning of the
project, approximately three years, being removed only for measurement.
39
Detectors in Test Incubations
The sample detectors in the routine incubations of the test series behaved similarly to the other
thermal samples in each specific incubation. That is, they displayed similar fading characteristics, levels of fading, and color shifts that were outlined for the thermal samples in the sections
dealing with each individual incubation. All of the incubations resulted in severe fading of
these samples with 60% to 70% of the beginning density being lost during each incubation
period. The housing did not impede or promote the diffusion of gases to the samples enclosed,
and there was no pattern of attack caused by the configuration of the housing’s louvers. The
plastic of the enclosure did not affect the tests in any way. Total exclusion of light in the test
chambers was probably not a factor in evaluation because the gases would have overwhelmed
any light-induced fading of the samples.
Detectors Distributed in the Office Space
It was interesting to observe the progression of attack on these samples. Regardless of the positioning of the housings, all of the samples lost approximately 10% of their beginning density
after a two-month period. Light was not a factor in the rate of fading of the samples, as those
that were fully exposed to the room light lost no more density than those that were in the
housings. Furthermore, the sample that was kept completely in the dark lost the same 10% of
its density over the same time period. After this initial period, the fading rate of the material
slowed down considerably. For instance, over the next eight months the samples lost only an
additional 2% or 3% of original density. Again, all samples faded at a similar rate regardless
of their positioning. At the end of the three-year test period, all samples had lost about 25%
of beginning density. None of the samples in the open office space exhibited any of the color
shifting seen in the nitrogen dioxide incubations. The configuration of the detector housing
did not affect the distribution of the atmosphere into the package. There was no pattern of
attack that would indicate any blocking of diffusion.
Conclusions/Plans for Development
The results of these tests suggest that the rate of fading of the thermal material may be
density-dependent or that a surface layer of oxidized dye acts to slow the subsequent rate of
fading over time. Comparison of the density loss over one year in the open office space to the
one-year, 0.1-ppm ozone incubation, (assuming an average concentration of 0.020 to 0.025
ppm in the open office) yields a good correlation of time versus concentration. However, the
control samples that were incubated in a chamber at 25°C and 50% RH for one year did not
demonstrate the 10% to 12% fading shown by the samples in the open office at a slightly
lower average temperature. This might be explained by the increased air movement in the
40
incubation chamber, which possibly aided the decomposition of available ozone on contact
with the chamber walls.
Further development of this monitor would be possible, and, in the end, such a monitor
would probably be a viable, inexpensive method of detecting high levels of ozone in the collection environment. However, the problems and negative aspects involved in moving forward
with this idea are felt to outweigh the benefits to be gained from the finished device. In the
first place, the thermal print material is no longer produced. Realizing that this material was
very sensitive and susceptible to fading by high temperature, light, and atmospheric pollutants,
Kodak has revised its processing and added a polymer coating that makes the new generation
of dye sublimation prints much more resistant to fading. If future development of this monitor technology is contemplated, a new, highly sensitive detector will need to be found. Also, a
more precise calibration of lower levels of ozone (from 0.001 to 0.1 ppm) would be necessary.
Furthermore, the threat to chromogenic color materials that was thought to exist has been
defused by this and other research. It has been demonstrated that the major concern for color
collections is not atmospheric pollution but high temperature. If color collections must be
retained for long periods of time, they must be stored in cool to cold conditions; if they are,
the mechanisms of oxidative fading will also be reduced relative to temperature. As has been
pointed out, in real-life situations, spot-wise or partial fading of chromogenic color materials
simply does not happen in the dark. Partially exposed color prints that remain on display for
extended periods will definitely exhibit increased fading of the print where it is exposed to the
light, but exposure to pollutants probably adds little to the total amount of fading. Given these
factors, is it important to know if high levels of oxidants are present in the collection atmosphere? For chromogenic color collections probably not. For mixed collections, pinpointing
high levels of oxidants would be useful as one aspect of environmental evaluation.
41
Conclusions
1. Although some of the most sensitive imaging materials in Phase I did display a great
deal of dye fading, most of the popular color and silver-based photographic output materials
were not affected by the pure oxidizing atmospheres they were exposed to. The total exposure
represented by these incubations would only be equivalent to about four years in a fairly polluted urban setting with no HVAC system controlling the input air of a storage space. Using
higher concentrations of pollutant gas has proven that many of the commonly used modern
photographic materials are sensitive to oxidative attack. This is especially true of chromogenic
color materials whose dyes fade rapidly in the presence of high levels of oxidants; in real life,
however, the time required for equivalent pollutant dosage would require several decades at
ambient levels. In this time frame the inherent sensitivity of these dyes to heat would have
caused them to fade a great deal more than the oxidant gases. If the materials were stored in a
cool/cold environment, the dye fading would be much reduced, but the action of any oxidants
would be diminished by an equal amount as their mechanisms are temperature-dependent also.
It can be concluded that, although chromogenic color materials are sensitive to oxidant gases,
they are more sensitive to high temperature and are not overly threatened by typical ambient
concentrations of pollutant gases in the storage environment.
Silver-based imaging materials, as has been noted in previous research, are not highly
sensitive to pure oxidant gases. Ionic silver is formed by oxidation, but, if no reducing agent
is present, the oxidation/reduction cycle of silver image deterioration can not move forward.
There is little doubt that high levels of oxidant gases combined with background levels of
acidic/reducing gases in storage atmospheres will attack image silver over time. Therefore,
supplementary HVAC and filtering is recommended for these collections. As mentioned above,
cool/cold storage will further mitigate deterioration of silver images.
2. Phase II of this project explored the synergistic effects of gas combinations. Its primary aim was to recreate the oxidation/reduction deterioration cycle of silver images. While
there were occurrences of some forms of image degradation in these experiments, the most
interesting finding is the fact that interactions between the constituent gases diminished the
effectiveness of gas combinations. Reduced dye fading of the color materials was noted in all
of the gas mixtures. This would seem to indicate that gases in the atmosphere act upon each
other to reduce their individual concentrations and lessen their effects, but this study did not
evaluate the long-term ramifications of absorbed gases and their role in future deterioration.
3. As seen in Phase III, enclosures for photographic materials offer physical protection
against handling damage and add extra support to delicate objects, but their advantages in
stopping the diffusion of atmospheric gases is minimal. Enclosures made of multiple layers
42
(an object in a sleeve, in a box, in a drawer), will certainly slow down the ingress of polluted
air, but the inside and outside atmospheres will equilibrate relatively rapidly. Enclosures made
of plastic can protect objects to the extent that they are in intimate contact with them, while
paper enclosures will not stop the diffusion of gas into the enclosure package. Encapsulation in
plastic offers almost complete protection against the atmosphere but also traps any deterioration by-products in the enclosure, thereby accelerating any autocatalytic forms of deterioration.
Buffered paper did not give any extra protection against pollutant attack, but buffering does
prolong the service life of the enclosure itself.
4. Development of an inexpensive passive ozone monitor for storage environments was
undertaken as part of this research. While the results of this development work were positive,
a more precise calibration of the device at lower gas concentrations is needed. The concentration range of 0.001 to 0.1 ppm (more typically found in storage spaces) should be evaluated
more closely. In addition, the Kodak dye diffusion transfer print media is no longer made.
If further development of this monitor is contemplated, a new detector must be found. It is
reasonable to expect that there are alternatives to this material, possibly a very sensitive dye
specially coated on a paper support, but it must be researched. The main concern that led to
the idea of the ozone monitor was the fading of chromogenic color dyes, which were thought
to be extremely sensitive to oxidative fading; these dyes have been shown to be much more
resistant than was thought. With this in mind, the benefits of this device are somewhat lessened, at least for photo archives applications.
43
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44
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