Vincent Posted September 12, 2009 Report Share Posted September 12, 2009 I've got this East German 1953 5 pfennig coin. I just don't understand howcome it can have these protruding bumps on obverse and reverse. Had they been smaller, it could be explained by accidental cavities in the dies. Had it been a tin coin it could be explained by changes in the composition of the metal caused by temperature, etc. This is, however, an aluminium coin (with a tiny addition of manganese). Any suggestions? Link to comment Share on other sites More sharing options...
Vfox Posted September 12, 2009 Report Share Posted September 12, 2009 Aluminum, just like iron can "rust", or in this case the metal degrades into aluminum oxide growths. It is a similar process to that of ferrous metal decay. Anyway, with this coin it is likely that a small ding or scrape allowed moisture to maintain itself in one spot for a time and started to oxidize the metal. Once the process starts, the oxide starts to grow and split the metal. Once that happens the oxide growth can start within the small fractures and just like ice on a wintry roadway, split the metal open and form bulges in it. I've seen it many time on tin, zinc, and aluminum artifacts (including coins) that have been exposed to the elements over quite a period of time. It's an interesting example of the breakdown of materials, something I'm keenly interested in with my artwork and as a numismatist. Thanks for sharing. Link to comment Share on other sites More sharing options...
amac44 Posted September 12, 2009 Report Share Posted September 12, 2009 I've got this East German 1953 5 pfennig coin. I just don't understand howcome it can have these protruding bumps on obverse and reverse. Had they been smaller, it could be explained by accidental cavities in the dies. Had it been a tin coin it could be explained by changes in the composition of the metal caused by temperature, etc. This is, however, an aluminium coin (with a tiny addition of manganese). Any suggestions? No nice find! but it just maybe a bad mix that the planchet was made of Link to comment Share on other sites More sharing options...
Vincent Posted September 13, 2009 Author Report Share Posted September 13, 2009 Thank you for comments! Link to comment Share on other sites More sharing options...
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