William Hoffman and Ralph Spohn
The conservation of complex composite artifacts can pose a real challenge for conservators. Different material types often require dissimilar treatment methods, which can be incompatible between materials, resulting in the potential to damage one while attempting to conserve another. Therefore, when determined necessary, the decision can be made to disassemble an object, treat component parts separately, and then reassemble after treatment. This approach can be especially difficult for objects recovered from archaeological sites. The effects of the burial environment can lead to the hardening and embrittlement of organic materials and corrosion and de-alloying of metals. In both scenarios, this can result in an inability to easily and safely take part archaeological objects requiring the development of new treatment techniques and procedures.
Between 1998 and 2002, over 210 tons of artifacts from the wreck site of the Civil War ironclad USS Monitor were recovered off Cape Hatteras, North Carolina by archaeologists from the National Oceanic and Atmospheric Administration and US Navy divers. Many of the retrieved artifacts came from the vessel’s engine room which included five steam engines and an assortment of plumbing assemblies. Having spent nearly 140 years on the seafloor, the cast iron elements of these artifacts had de-alloyed through graphitic corrosion and now possessed the structural integrity of chalk. If that was not challenging enough, a majority of the “graphitized” objects had attached component parts which had become adhered together by rubber gaskets that had hardened having lost their elasticity over time.
Early in the treatment of these artifacts, it was clear that some level of disassembly would be required so that organic, copper alloy, and iron alloy elements could receive independent treatment. However, any attempt to separate the objects into their component parts led to the cracking or breaking of the fragile “graphitized” material due to the rigidity of the gaskets. Fortunately for the conservation staff, during the application of a routine hot treatment technique used to removed concretion from copper alloy artifacts, it was discovered that a temperature of approximately 160 degrees Fahrenheit caused a previously hardened rubber gasket to soften an become pliable. This revelation led to the hypothesis that one potential solution to the disassembly conundrum could be to submerge the artifacts in a hot water bath and allow the transmission of heat to soften the gasket material; thus, limiting damage to the de-alloyed cast iron during disassembly. Additional experimentation to identify the effects of an elevated temperature on “graphitized” cast iron samples followed. Positive results from sample testing led to the design and construction of a heated water system and the development of a treatment procedure for artifact disassembly. This paper will provide an overview of the project and the operation the hot water tank apparatus. In addition, other potential treatment uses for the machine will be highlighted.