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The differentiation of commercial inks on the bases of physical and
chemical analysis by the Video Spectral Comparator and Thin Layer
Chromatography
Rebecca Glover*1, Alexandra Furlought1, Pardeep Jasra1, Shashi K. Jasra1
Abstract:
Differentiating inks by chemical and physical analysis is an essential forensic step in question
document investigation. This article aims to further differentiation methods by using a video spectral
comparator. Inks were first subject to thin layer chromatography and observed in the video spectral
comparator under normal, ultraviolet, and infrared light. Each ink was then used to write the word
“Forensics” and observed under the same conditions. Finally, the inks were overlapped, and observed under
the various lights to see if distinguishability was possible. Most successful under infrared light, this method
allowed for differentiation between 12 of the 15 inks based on fluorescent activity.
Keywords: Forensic science, video spectral comparator, thin layer chromatography, ink
1 Forensic Sciences, University of Windsor, 401 Sunset Avenue, Windsor, Ontario
* Communicating Author Contact: [email protected]
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Introduction
Differentiating inks by chemical and physical analysis is an essential forensic step in question
document investigation. Forensic Document Examiners will confirm or exclude the original ink
used to produce the document, as well as identify any other ink present. The application of this
procedure largely involves documents with financial values, wills, cheques etc., suspected of
modification4. Given the potential life impacting consequences of the evidence, there is a need for
the commitment to the development of a database that will allow for shared and peer-reviewed
communication of in-depth research done on the examination of inks. Including a system of
unbiased regulation of conclusions and protocols regarding the confirmation, exclusion and
undetermined decisions made when analysing ink guided by pre-determined requirements.
The process of examination and documentation begins with one of two methods; destructive
and non-destructive analysis of the questioned documents1. With each extraction resulting in the
physical damaging of the pen itself or part of it, obtaining ink samples for the chromatography
plates in TLC is a destructive type of data collection1. Thin-layer chromatography is an
inexpensive and fast acting experiment that can take as little as 15 minutes to develop. The process
functions on the basis of particle size and solubility of the sample being added to the solvent. The
sample is then drawn up the plate by capillary action of the solvent, taking selected compounds
from the sample mixture with it to certain degrees. Solubility effects how far a substance will travel
depending on the solvent used; less soluble compounds will travel further up the silica TLC plate
(stationary phase) with the solvent (mobile phase)3. By measuring the distance travelled by
compounds after development, an Rf value can be calculated. Rf values mathematically compares
the distance that the sample has moved to the distance that the solvent has traveled up the plate,
which is independent of the sample.
Many forensic analytical methods exist to discriminate between inks combining
chromatography and optical technologies, with positive results and contributions2. Questioned
documents or developed TLC plates examined by a video spectral comparator is non-destructive;
it is harmless as taking a picture. The forensic contribution of the video spectral comparator is the
ability to differentiate between types of ink by using alternative light sources highlighting material
heterogeneity2. The technology visualizes the individual properties of the ink depending on the
wavelength being used. The camera captures molecules of the smallest size with enough sensitivity
to accurately represent what the forensic document examiner is seeing to justify their final
conclusion. Photographs taken and saved contain all relevant information such as time,
wavelength, date, etc., to ensure strict documentation.
The aim of this research is to evaluate the potential and continued gain that will come from
the development of a database created by video spectral comparator analysis, an easy to use, multilight source system capable of producing detailed images for comparison and exclusion. Combined
with thin-layer chromatography, chemical characteristics as well as physical can be documented
to increase reference information available for present and future forensic investigations.
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Materials and Methods
A sample of 15 black commercial inks was selected from local retailers. These inks were
chosen to represent various brands as well as ink types, while highlighting popular consumer
choice. The written samples were all written on BASICS printer paper to remove variability of
reactivity between different companies.
List of studied black inks:
Ink Number
Commercial Name
1
Z-Grip
2
Round Stic
3
Ball Point Pen
4
R.S.V.P Super RT ®
5
VF Hi-Techpoint
6
Soft Grip
7
Point FriXion
8
Stylus Pen
9
DARK
10
FriXion Colours Marker Pen
11
Uni Deluxe
12
Sharpie Pen
13
Roller Ball Pen
14
Gel Ink Pens
15
Sonix Gel
15 labeled TLC plate lanes were prepared to separate the dyes, pigments, enhancements and
other additives of the ink mixture. A sample of ink approximately 0.5um was administered to the
pre-marked line of the TLC plate in respect to ink and lane number. To construct the TLC
chambers, acetone was used as the solvent and aluminum foil to cover and prevent evaporation.
The plates developed for 15 to 20 minutes or longer until the solutions finished ascending the plate
by capillary action of the solvent. Observations of data such as Rf value and fluorescent response
were documented in addition towards later database submissions and experimental comparisons.
In designated groups, each ink was used to write “Forensics” with a number indicating the
identity relative to TLC plate placement. The Foster and Freeman® Video Spectral Comparator
40 High Definition (VSC®40/HD) was used to measure the reflectance of the inks in both the TLC
plates and the written samples over a range of 312nm to 850nm.
In groups of three to four, the inks were written in overlapping patterns in attempt to obscure
text. Using the same wavelengths, the inks were differentiated using the VSC® 40/HD.
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Results & Analysis
Inks 1-6, 8, 9, 11, 13 and 14 showed development on the TLC plates. Each was
distinguishable by colour and Rf value. At 312nm, components of the ink, visible as colours under
normal light, did not react to the light source and darkened to a black image; most prominently
seen at the baseline. Solutions in the mixture that did react to the ultraviolet light source displayed
colour emphasis and or/alteration. The solutions in inks 7 and 10 traveled the same distance as the
solvent, resulting in an Rf value of 1. They both showed a faded purple colour at the top of the lane
with a barely visible streak. At 312nm, the UV light visualized the components not seen under
normal light and the purple colouration fluoresced orange for both inks.
Under infrared wavelengths, fluorescent properties of the inks were visualized (except 12
and 15). The samples in lanes 12 and 15 did not develop in the TLC and did not travel with the
solvent, remaining at the base line. Samples 12 and 15 remained undetectable under ultraviolet
and infrared exposure.
Using the VSC®40/HD, the inks were subjected to infrared light to determine fluorescent
properties. Inks 1, 6, 11, 12, and 15 did not fluoresce under infrared light. Inks 4 and 14 showed
minimal fluorescence at 645nm. Inks 2 and 13 showed mild fluorescence at 645nm. Inks 3, 7, 9,
and 10 brightly fluoresced under infrared light. Inks 5 and 8 increased in fluorescence in proportion
to the wavelength. At 645nm, Ink 5 did not fluoresce, but showed minimal fluorescence at 780nm.
Ink 8 showed a mild fluorescence at 645nm, and increased to a bright fluorescence at 780nm.
There were no significant results observed under ultraviolet light.
When overlapped and obscured, there were no differentiating characteristics between inks
under both normal and ultraviolet light. Under infrared light, the unique fluorescent properties
allowed the inks to be identified to varying degrees. Test 2 reflected the ink properties found in
Ink 5’s individual test, which increased in fluorescence, blending with Inks 7 and 8. A red spot
filter was also used on Test 2, which eliminated Ink 7, but revealed indentations in the paper. In
Test 3, Inks 11 and 12 were found to be indistinguishable when examined through the infrared
spectrum using a blue filter. Tests 1 and 4 were differentiable between all inks under infrared light.
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Table 1 – Commercial Ink Index
Ink
Number
Commercial Name
Company
Manufacturer
Made In
Details
1
Z-Grip
Zebra
Zebra ® Pen Canada Corp
China
Medium point, latex free
2
Round Stic
Bic
BIC Inc.
Mexico
Medium point
3
Ball Point Pen
@theOFFICE
China
Medium point
4
R.S.V.P Super RT ®
Pentel
Walmart Canada
Pentel Stationary of
Canada Ltd.
Mexico
Small point
5
VF Hi-Techpoint
Pilot
Mexico
Small point
6
Soft Grip
PaperMate
Crestor
Newell Rubbermaid
Office
Korea
Large point
7
Point FriXion
Pilot
Crestor
Japan
Erasable pen
8
Stylus Pen
Onyx Green
Onyx + Blue Corporation
China
4 in 1 pen, recycled aluminum
9
DARK
Maped
Maped
China
Medium point
10
FriXion Colours Marker Pen
Pilot
Crestor
Japan
11
Uni Deluxe
Uniball
12
Sharpie Pen
Sharpie
Newell Rubbermaid
Office
Newell Rubbermaid
Office
Marker Style pen, erasable pen
Fluid roller, 0.5mm, "helps
prevent cheque fraud" - super
ink
Fine tip, liquid pen, water
resistant
13
Roller Ball Pen
Office Works
Office Works
14
Gel Ink Pens
KAMSET
15
Sonix Gel
Staples
Japan
Japan
0.55mm liquid ink
KAMSET
China
China, ink in
Germany
Staples
China
Retractable gel pen
Table 2 – Distance traveled by Commercial Ink in Thin-Layer Chromatography
Ink
Number
1
Solute Travelled
(mm)
33
Solvent Travelled
(mm)
54
Rf Value
0.61
2
18
53.5
0.34
3
36
54.5
0.66
4
27.5
55.5
0.50
5
32.5
48.5
0.67
6
49
49
1
7
49
49
1
8
27
50
0.54
9
34.5
49
0.70
10
41
48.5
0.85
11
19
33
0.58
12
0
47.5
0
13
13
55.5
0.23
14
44.5
45
0.99
15
0+
54
0
Free ink roller
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Table 3 – Separated Commercial Ink response to Video Spectral Comparator
Ink
Number
1
2
3
4
TLC plate - Normal light
Fade from black to dark red,
components clearly visible
Fade from black to orange to yellow,
components clearly visible
Fade from black to dark orange,
components clearly visible
Thinner, fade from black to orange to
yellow, components clearly visible
6
Fade from black to blue, with
darkness at top
Dark red, consistent throughout run,
darkness at top
7
Grey at ink deposit, no runs shown
Light purple at top (separated)
5
TLC plate - Infrared light
Almost no fluorescence
TLC plate - Ultraviolet light
Bright red and orange in
components
Mild fluorescence
Bright grey in components
Very bright fluorescence
Very little fluorescence
within ink, some above
Some grey in components
Little fluorescence
Almost no fluorescence
Orange streaks along run
Dark, no
fluorescence/colouration
Very bright fluorescence,
run visible
Run faint but visible, burgundy
colour at top
Mild fluorescence
Mild orange colour on sides,
grey at top
Some grey separated from ink
9
Fade from black to dark orange,
components clearly visible
Fade from dark red to orange,
components visible
10
Light purple colour across run
Very bright fluorescence
Bright red and orange
11
Charcoal colour
No fluorescence
Dark, no
fluorescence/colouration
12
Nothing visible
Nothing visible
14
No run shown
Fade from black to yellow,
separation, and orange at top
Fade from black to blue/white, back
to black at top
Mild fluorescence
Large fluorescence but not
very bright
Dark, separated, yellow at top
Dark, no
fluorescence/colouration
15
No run shown
Nothing visible
Slight blue hue at top
8
13
No fluorescence/colouration
Distinguishable
with coverage
Yes, best at 725,
none at UV
Yes, best at 725,
none at UV
Yes, best at 725,
none at UV
Yes, best at 725,
none at UV
Yes, best at 715,
fades at 850, none
at UV
Yes, best at 715,
none at UV
Yes, best at 715,
fades to
etchmarks under
red, none at UV
Yes, best at 715,
fades to
etchmarks under
red, none at UV
Yes, best at 715,
none at UV
Yes, best at 715,
none at UV
Yes except from
12, best at 715,
none at UV
Yes except from
11, best at 715,
none at UV
Yes at 645, none
at UV
Yes at 645, none
at UV
Yes at 645, none
at UV
Figure 1 (left) – Commercial ink TLC 1-4 (left to right) under normal white flood light. Figure 1.1 (right) –
Commercial ink TLC 1-4 (left to right) under Ultraviolet light @ 312nm.
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Figure 1.2 (left) – Commercial ink TLC 1-4 (left to right) under Infrared light @ 645nm with red spot filer. Figure
1.3 (right) – Commercial ink TLC 1-4 (left to right) under Infrared light @ 725nm with red spot filter.
Figure 2 (left) – Commercial ink TLC 5-8 (left to right) under normal white flood light. Figure 2.1 (right) –
Commercial ink TLC 5-8 (left to right) under Ultraviolet light @ 312nm.
Figure 2.2 (left) – Commercial ink TLC 5-8 (left to right) under Infrared light @ 645nm with red spot filter. Figure
2.3 (right) – Commercial ink TLC 5-8 (left to right) under Infrared light @ 725nm with red spot filter.
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Figure 3 (left) – Commercial ink TLC 9 (far left) under normal white flood light. Figure 3.1 (right) – Commercial ink
TLC 9 (far left) under Ultraviolet light @ 312nm.
Figure 4 (left) – Commercial ink TLC 10-12 (left to right) under normal white flood light. Figure 4.1 (right) –
Commercial ink TLC 10-12 (left to right) under Ultraviolet light @ 312nm.
Figure 4.2 (left) – Higher magnification of commercial ink TLC 10-12 (left to right) under Ultraviolet light @ 312nm.
Figure 4.3 (right) – Commercial ink TLC 10-12 (left to right) under Infrared light @ 850nm.
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Figure 5 (left) – Commercial ink TLC 13-15 (left to right) under normal white flood light. Figure 5.1 (right) –
Commercial ink TLC 13-15 (left to right) under Ultraviolet light @ 312nm.
Figure 5.2 (left) – Commercial ink TLC 13-15 (left to right) under Infrared light @ 645nm. Figure 5.3 (right) –
Commercial ink TLC 13-15 (left to right) under Infrared light @ 850nm.
Table 4 – Ink response to alternating wavelengths by Video Spectral Comparator
Ink
Number
VSC - Normal Light
VSC - Infrared
light at 645nm
VSC - Infrared
light at 715nm
VSC - Infrared
light at 780nm
VSC - Infrared
light at 850nm
VSC Ultraviolent at
312nm
1
Dark ink, but patchy
No fluorescence
No fluorescence
2
Dark ink, but patchy
Mild fluorescence
No fluorescence
3
Dark ink, but patchy
No fluorescence
4
Dark ink, but patchy
Bright fluorescence
minimal
fluorescence
No fluorescence
Slight
fluorescence
Slight
fluorescence
Barely visible
Very bright
fluorescence
Bright
fluorescence
Nothing visible
Mild
fluorescence
Slight
fluorescence
5
Dark ink, straight through
No fluorescence
Nothing visible
6
Dark ink, but very patchy
No fluorescence
7
Light ink
Bright fluorescence
8
Dark ink, but patchy
Mild fluorescence
9
Fluorescent
Bright fluorescence
No fluorescence
11
Dark ink, but patchy
Thick, medium ink,
hesitation marks clear
Dark ink, but some
patches
No fluorescence
Very bright
fluorescence
Brighter
fluorescence
Bright
fluorescence
No fluorescence
No fluorescence
12
Dark ink, straight through
No fluorescence
No fluorescence
13
Dark ink, straight through
Mild fluorescence
No fluorescence
14
Dark ink, straight through
Slight fluorescence
No fluorescence
10
No fluorescence
No fluorescence
No fluorescence
No fluorescence
No fluorescence
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15
Dark ink, straight through
No fluorescence
No fluorescence
Figure 6 (top left) – Commercial ink document 1-4 under normal white flood light. Figure 6.1 (top right) –
Commercial ink document 1-4 under Ultraviolet light @ 312nm. Figure 6.2 (bottom left) – Commercial ink
document 1-4 under Infrared light @ 645nm.
Figure 7 (top left) – Commercial ink document 5-8 under normal white flood light. Figure 7.1 (top right) – Commercial
ink document 5-8 under Ultraviolet light @ 312nm.
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Figure 7.2 (top left) – Commercial ink document 5-8 under Infrared light @ 645nm. Figure 7.3 (top right) –
Commercial ink document 5-8 under Infrared light @ 715nm. Figure 7.4 (bottom left) – Commercial ink document 58 under Infrared light @ 780nm. Figure 7.5 (bottom right) – Commercial ink document 5-8 under Infrared light @
850nm.
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Figure 8 (top left) – Commercial ink document 9 under normal white flood light. Figure 8.1 (top right) –
Commercial ink document 9 under Ultraviolet light @ 312nm. Figure 8.2 (bottom left) – Commercial ink document
9 under Infrared light @ 715nm.
Figure 9 (top left) – Commercial ink document 10-12 under normal white flood light. Figure 9.1 (top right) –
Commercial ink document 10-12 under Ultraviolet light @ 312nm. Figure 9.2 (bottom left) – Commercial ink
document 10-12 under Infrared light @
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Figure 10 (top left) – Commercial ink document 13-15 under normal white flood light. Figure 10.1 (top right) –
Commercial ink document 13-15 under Ultraviolet light @ 312nm. Figure 10.2 (bottom left) – Commercial ink
document 13-15 under Infrared light @ 645nm.
Figure 11 (left) – Commercial ink TEST document 1-4 under normal white flood light. Figure 11.1 (right) –
Commercial ink TEST document 1-4 under Ultraviolet light @ 312nm.
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Figure 11.2 (top left) – Commercial ink TEST document 1-4 under Infrared light @ 645nm. Figure 11.3 (top right)
– Commercial ink TEST document 1-4 under Infrared light @ 695nm. Figure 11.4 (bottom left) – Commercial ink
TEST document 1-4 under Infrared light @ 725nm.
Figure 12 (left) – Commercial ink TEST document 5-8 under normal white flood light. Figure 12.1 (right) –
Commercial ink TEST document 5-8 under Ultraviolet light @ 312nm.
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Figure 12.2 (top left) – Commercial ink TEST document 5-8 under Infrared light @ 645nm. Figure 12.3 (top right) –
Commercial ink TEST document 5-8 under Infrared light @ 715nm.
Figure 12.4 (top left) – Commercial ink TEST document 5-8 under Infrared light @ 850nm. Figure 12.5 (top left) –
Commercial ink TEST document 5-8 under Infrared light @ 850nm. Figure 12.6 (bottom left) – Commercial ink
TEST document 5-8 under Infrared light @ 715nm using a red spot filer.
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Figure 13 (top left) – Commercial ink TEST document 10-12 under normal white flood light. Figure 13.1 (top right)
– Commercial ink TEST document 10-12 under Ultraviolet light @ 312nm. Figure 13.2 (bottom left) – Commercial
ink TEST document 10-12 under Infrared light @ 645nm. Figure 13.3 (bottom right) – Commercial ink TEST
document 10-12 under Infrared light @ 715nm.
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Figure 14 (top left) – Commercial ink TEST document 13-15 under normal white flood light. Figure 14.1 (top right)
– Commercial ink TEST document 13-15 under Ultraviolet light @ 312nm. Figure 14.2 (bottom left) – Commercial
ink TEST document 13-15 under Infrared light @ 645nm.
Discussion:
Nearly all of the inks could be distinguishable with a combination of Thin Layer
Chromatography and Video Spectral Comparison. Thin Layer Chromatography showed the
chemical properties, such as the solubility and the Rf value, while Video Spectral Comparison
showed the physical properties, such as the fluorescent activity.
The two inks that did not show distinguishable results under either TLC or VSC are inks
12 and 15. The inks did not elute in TLC, which could show that they are primarily pigment
based5.
Ultraviolet light did not react with the inks under written document analysis, but showed
distinction between inks in the TLC analysis. When the TLC plates were subject to UV light, each
ink showed distinctive colours and patterns. Inks 12 and 15 did not show up on the run, and need
further analysis.
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The inks in both the TLC and VSC fluoresced under infrared light. This is where the
primary individualization of inks was found. The different components of the inks within the TLC
plate fluoresced separately, which can also individualize them. Under the VSC, marker style inks
fluoresced brightly, while liquid inks showed little fluorescence. There is also continuity between
manufacturers, as Newell Rubbermaid Office® produces both large point pens and liquid ink pens;
none of which fluoresced.
These results are applicable in the analysis of forged documents such as cheque forgery,
signature forgery, and fraud. It could also be used for the standardization of inks used by
professionals such as the police force for their notes. Based on their variance in reflectance under
infrared light, inks can be distinguishable when overlapped. These findings can also be used to
create a peer-reviewed comparative database, to which document analysts can compare unknown
inks.
Further analysis could be improved in various ways. Ethyl acetate would be a better solvent
in the TLC analysis than acetone. Acetone has both polar and nonpolar properties, so the
intermolecular interactions with vary – it is better to use a solvent either highly polar or highly
nonpolar. Further research could be conducted via gas chromatography mass spectrometry to
determine the components of each ink. This research could also be furthered using RGB analysis,
as per Djozan et al 1. The data is also not numerical but subjective, and a measured reflective curve
would further support the data. Time could also be used as a variable, to see if the same ink can be
distinguished after separate writing occurrences.
Conclusion
Differentiation was possible between the 15 commercial black inks used in this experiment;
with exceptions between inks 11, 12 and 15: recommended to undergo further examination by
video spectral comparison utilizing the various features of the technology. Ultraviolet light at
312nm was most prominently useful in examining the separated components of the TLC plate, but
did not provide any significant results when applied to the written documents and overlapping
inks. Infrared light (645nm-850nm) was successfully used in all stages of the experiment to
observe the physical properties of the inks in regards to fluorescent activity.
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Acknowledgements
I would like to acknowledge the University of Windsor’s Forensic Science Department for
their funding and use of equipment and space. Specifically, Dr. Shashi Jasra and Dr. Pardeep Jasra,
who were co-supervisors for this research and to my family and friends for their continued support.
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