Silver Surface Enrichment On A 1964 Kennedy Half Dollar

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Author	Replies: 2 / Views: 1,127
colonialjohn Pillar of the Community United States 1757 Posts	Posted 02/05/2018 9:16 pm As a few in this Red Book Channel know I am mostly into U.S. Colonials or older coins such as 19th or 18th C Spanish/American coins. At times some collectors have asked me how can a Eight Reale coin have a surface silver reading value of 95% if the silver alloy of the piece has been originally alloyed at 92%? Silver surface enrichment with time say over 200 years may give rise to silver surface values to increase above its original silver alloy value. I have examined salt water corrosion (i.e., Shipwreck) 1783 Carolus III Silver Dollars with almost 99% Ag since all the copper basically has leached out.Actually most will read 96-99%! What does this have to do with a 1964 Kennedy? Using microstructure analysis do we see ANY? copper migrating to the surface on a coin only as old as say a half a century? Not much! See this link: https://www.cambridge.org/core/serv...oins-div.pdf Still confused? Inquire here ... It takes time for this effect like silver coins at the bottom of the ocean as part of shipwreck. See this paper (Google it): Silver surface enrichment of silver-copper alloys: A limitation for the analysis of ancient silver coins by surface techniques L. Beck, S. Bosonnet, S. Re #769;veillon, D. Eliot, F. Pilon John Lorenzo Numismatist United States Edited by colonialjohn 02/05/2018 9:38 pm Report this Post to the Staff

sel_69l Bedrock of the Community Australia 21786 Posts	Posted 02/06/2018 12:43 am Copper will leach out in preference to silver with salt water corrosion. With electro plating on a copper coin, there is migration of copper into the silver, and silver into the copper, over a period of many decades. The Incas surface enriched many of their gold artifacts. The body alloy was often around 60%, but the object, prior to working into a finished object was immersed in a corrosive liquid, which leached the copper out of the surface. The metal was then beaten into the thickness required, then worked into the finished object. I have gold thin plated a sterling silver coin. Over a period of 20 years or so, the coin has become more pale looking, despite always being protected in a sealed acrylic capsule since plating. Another instance of silver gold exchanging places. I am not sure how a 90% silver '64 Kennedy would become unstable, unless subjected to some sort of corrosion. That corrosion would be deleterious, and obviously noticeable. Report this Post to the Staff
colonialjohn Pillar of the Community United States 1757 Posts	Posted 02/06/2018 09:50 am Excellent sei_691 ... my point was it takes time for silver surface enrichment to act - I had the opportunity one day in the lab at EDAX to analyze something on their SEM/EDS so we cut a 1964 Kennedy Dollar in half and looked to see at the microstructure from surface to core to see if there was any copper movement. Not too much was noticed on any copper moving or aggregating to the surface. Its no wonder say on New Orleans Morgan dollars on why they tone so nice as compared to other mints with the high heat and duration of these coins as compared to other mints in the late 19thC/early 20thC. Report this Post to the Staff
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