Hot tub time machine: A heated water system for artifact disassembly and treatment

William Hoffman and Ralph Spohn


Starting in 1998, more than 200 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 retrieved objects came from the vessel’s engine room, which included five steam engines. Early in the conservation of these artifacts, it was identified that some level of disassembly would be required so that organic, copper alloy, and iron alloy elements could receive independent treatment. However, it was found that many cast iron components had de-alloyed and now possessed the structural integrity of chalk. Attempts made to separate some of the fragile parts adhered together by semi-hardened rubber gaskets led to damage. Fortunately, it was discovered that a temperature of approximately 73˚C caused the gasket material to become pliable. This led to the idea that a hot water bath could be utilized to transmit heat through de-alloyed cast iron, enabling the softening of gasket material and the safe disassembly of components. This article provides an overview of the development and operation of a hot water apparatus for component separation. In addition, a test trial for the machine in the re-treatment of copper alloys will be discussed.

KEYWORDS: Marine archaeology, Composite artifact, Gasket, Graphitized cast iron, Tankless hot water, USS Monitor

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