Minimal Intervention on Historic Metallic Objects at
Fort Sumter National Monument
Amy Elizabeth Uebel MSHP, Liisa Nasanen MSc, Chris McKenzie BSc
Fort Sumter National Monument (including Fort Moultrie, Sullivan’s Island Lifesaving Station, and Charles Pickney Historic Site) retains
COSTS OF TRADITIONAL CANNON CONSERVATION
one of the largest and most comprehensive collections of outdoor ordnance in the United States. The bulk of this collection is displayed
Materials
outdoors and is freely accessible to the public with little to no barriers. Due to the size and the adverse environmental conditions, the ordnance
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Documentation &
have proven to be challenging to maintain, preserve, and keep accessible to the public. In 2008, the Park Service approached the Warren
Monitoring
Lasch Conservation Center of Clemson University to develop a new protocol for conservation treatment on a set of significant ordnance
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and metal architectural elements.
Rigging &
Transnportation
Over the preceding years, a wide variety of methods and coatings have been tested to determine the best balance between stabiliLabour
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ty, results, and minimal intervention to the historic surface. While traditional abrasive blasting methods proved successful and could be
performed with training to minimize substrate loss, the costs remained high. Rigging and transportation added to these expenses as did
abrasive blasting materials, labor, and monitoring that was performed in conjunction with the work. Additionally, many of these treatments exposed both the environment and the staff to potentially hazardous chemicals such as lead.
Implementing a system designed by Restorative Techniques for masonry cleaning, superheated pressurized water blasting with a corrosion
inhibitor proved to be an effective method to remove failing paint layers and loose corrosion without damaging the historic substrate. Additionally, this
method had the added advantage of allowing conservators to stabilize the substrate without necessitating the removal of existing mill-scale.
SUPERHEATED PRESSURIZED WATER BLASTING
TREATMENT OF ORDNANCE AND ARCHITECTURAL
HERITAGE: Case Study: 32pdr Model 1829 cannon
Flash corrosion is controlled through the application
of corrosion inhibitors under pressure. (Left) 32pdr
cannon prior to application of corrosion inhibitor
(Right) The same cannon several days after application
of corrosion inhibitor
Containment
Cost Comparison of Industrial Blasting Methods v. Superheated Pressure Blasting
$16,000
$14,000
Superheated Pressurized
Water Blasting on Historic Metals
ᐥᐥless expensive
ᐥᐥless invasive
ᐥᐥwork performed in situ
ᐥᐥminimizes release of hazardous materials into the
environment
ᐥᐥless harsh on environment
ᐥᐥno embedment of alien materials into historic fabric
ᐥᐥno extensive periods of wetness due to immediate
evaporation of superheated water
ᐥᐥtemperature and pressure tunable to material’s needs
ᐥᐥwork completed by conservators
ᐥᐥadditives, such as detergents and corrosion inhibitors
can be added to treatment medium
$12,000
Paint
Stripper/Lead
Reduction
$10,000
$8,000
$6,000
$4,000
$2,000
$-
Traditional w/ no lead
Labor
Traditional w/lead
Rigging & Transportation
Superheated Pressure Blasting
Documentation & Monitoring
Materials
Onsite Containment
Industrial Blasting Methods for
Metal Conservation
Superheated
Pressurized
Water Blasting
ᐥᐥexpensive
ᐥᐥinvasive
ᐥᐥtransportation risks damage to the artifact
ᐥᐥrelease of hazardous materials into environment
ᐥᐥcontracting of work to industrial service providers
necessary
• Application of
corrosion inhibitor
Painting
Specifically designed tampions were produced
to create a port system to seal off the barrel of
each gun where appropriate. A desiccant
was introduced into the barrels of all four
ordnance to ensure a microclimate to
minimize the possibility of corrosion
Microclimates
within the barrel. The special design of
the tampion allows for the installation of
a datalogging system into the interior of
the cannon. A USB connection housed in
the cap of the tampion allows for the data
to be downloaded with no disturbance to the
established microclimate.
From 2011-2012, WLCC worked with a local painting contractor
and riggining company to move and treat 8 cannon along “Cannon
Row” at Fort Moultrie on Sullivan’s Island. Various blasting methods,
using water or pressurized air as the fluid, the latter with a choice of
abrasive were compared for efficacy, and retention of historic fabric.
While SpongeJet with plastic beads was found to be efficient, gentle
to the historic surface, as well as able to minimize release of airborne
contaminants (e.g. lead if present), the cost prevented its extensive
use on the artifacts selected for the project.
Coatings at Fort Sumter National Monument
Coating Rating
12
10
8
Devflex 1B
6
MacroHS 15B
4
Macropoxy 646 3B
2
Corothane I 6D
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Tru-Glze 10B
A multi-year assessment of various industrial coatings in maritime enviroments was
implemented to examine the most suitable coatings for Fort Sumter National Monument.
Gloss, increase of corrosion, and color changes were noted at specific intervals to compare
industrial coatings. Conservators wanted to examine which systems withstood the harsh
climate while protecting the ordnance.
Maintenance
A WWII era signal light was treated
using superheated pressurized
water blasting. The light casing is
composed of several different alloys
of aluminum and
in many cases
maintained the
original anodized
coating. Using
this method, the
original coatings
were able to be
maintained while
the less historic
(and failing)
coating was
removed.