Silver or Not Silver?


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A beautifully preserved manometer was found attached to the engine. The gauge, which measures temperature and pressure, is currently under treatment. It has been dismantled as much as possible to assure better removal of the chlorides (e.g. the “conservators’ nightmare”). The main body of the gauge is made of copper alloy, and two wood stoppers enclose the top and bottom. The wood pieces are firmly embedded in the gauge and will therefore be treated intact and in contact with the copper alloy body. Former conservators carefully removed the mercury still in the glass component (see x-ray below), after which the glass part was separated from the gauge. This element is now fully conserved.

The scales were also separated from the gauge body and are currently being cleaned. They particularly attracted our attention because they seemed to be made of a silver alloy. However, the aspect of the corrosion products covering them was uncommon and the response of the metal to chemical cleaning tests was not what conservators expected from a silver artifact. Prior spot tests to identify the alloy were contradictory so it was decided to send one of the scales for an X-ray fluorescence analysis (non-destructive method) at the Northrop Grumman shipyard in Newport News. This silvered surface appeared to be a nickel alloy named nickel-silver or German silver. This alloy was mainly used due to its hardness and resistance to corrosion. Considering that 150ºF could easily be reached in the machines room, it makes sense that this alloy was used on a tool that needed to be readable at any time. Neat story!