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Characteristics of shrunken coins
Posted by Craig on 11/22/2003, 9:28 am I was fascinated by the interesting article by Theodore Gray in Popular Science on your process for shrinking coins. I would possibly be interested in having some selected coins processed in this manner, but first I would like a few details regarding exactly what I will receive. Specifically, will there be any density change? Any weight change? Will the thickness of the coin change, and in what direction and distribution(uniformly or unevenly). How about compositional changes(i.e. will all of the silver still be there). What about surface texture and oxidation? I look forward to hearing from you. Best regards, Craig R. Moyer
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Re: Characteristics of shrunken coins
Posted by Bert Hickman on 11/22/2003, 10:23 am, in reply to "Characteristics of shrunken coins" Thanks for your interest in our shrunken coins. Shrunken coins do become thicker as their diameter decreases. However, since their mass and volume stay the same, their density also remains the same as before. In some coins there may be a bit of relative shifting between the coin's surface features. For example, in cladded coins the pure copper center of the coin "feels" more compressive force than the poorer conducting nickel-copper outer layers. This can cause certain surface features to be "dragged" into other features on some coins. This is a very repeatable change. Also, since the forces exceed the yield strength of the metal, the resulting plastic flow causes previously mirror-like surfaces to gain a "frosted" appearance. In addition, many coins develop faint lines (called Luder's Lines) that seem to radiate outwards from the center of the coin. This can be fairly attractive as in the case of the Kennedy Half Dollar, where Kennedy's bust sometimes appears "haloed" by radiating Luder's Lines. The size of the crystalline grains of the coin's alloys becomes smaller (especially near the rim of the coin), and the metal becomes significantly work hardened. Finally, heating from the combination of metal working and the huge current pulse that's induced into the coin may cause a bit of surface discoloration for coins shrunk at high power levels. The alloy used in small silver alloy coins (i.e., older dimes and silver quarters) seems to change color to an unattractive greenish-brassy color, and I don't offer these coins for that reason. And the newer copper-plated zinc pennies simply explode in a shower of metal globules. The results on some coins can vary based on previous processing at the metal supplier or at the mint. For example, identially appearing Sacagawea dollars can turn out significantly different even when shrunk under identical conditions. The surface texture can range from very smooth to coursely granular. Fortunately, I can avoid getting very granular coins by judiciously selecting the mint and year of the coins. See: Sometimes, there may be hidden defects within a coin that only become apparent after shrinking: More information on the shrinking process and examples of the various effects can also be seen in the following articles: Shrinking is still somewhat of an art more than a science... :^) Thanks again and best regards, -- Bert --
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