Conservation Showcase: 1938 Proof Half Dollar

Posted on 8/23/2011

A recent example from our conservation laboratory.

NCS Conservation Showcase NCS Conservation Showcase
click to enlarge click to enlarge
NCS Conservation Showcase NCS Conservation Showcase

Holders designed to be convenient and offer some protection in the short term can lead to long term problems if the coin is left too long. This 1938 Proof Half Dollar was likely stored in a soft PVC laden flip for a good period of time. The plasticizer in the matrix of the coin holder material can leach out under normal conditions and deposit itself in the form of a green haze, with early stages of PVC contamination, to a thick green sludge, in more advance cases of contamination. This residue can etch into the surface metal of a coin causing irreversible damage.

The conservators at NCS were able to remove the green residue from the surface of this coin. After a first glance of the before image, the coin might make appear to be a mint state strike example but the deep mirrored surfaces are quite apparent once the haze is removed in the after image. Luckily for this submitter, the PVC residue had minimal effect on the surface metal and was removed just in time. This coin was able to grade with NGC using standard numeric grading following the conservation.

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