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<p>[QUOTE=&quot;desertgem, post: 1924405, member: 15199&quot;]Many studies show that the majority of verdigris is copper carbonate which is a bluish green compound with similar color to &#039;bronze disease&#039; as identified by various collectors of ancients. Copper carbonate ( and also other copper compounds such as copper sulfate which many people ae aware of) can be different amounts between greenish blue of pure copper carbonate and deeper blue of hydrated copper carbonate. In the lab we use higher heat than one gets on sand dunes of the middle east&nbsp; to change the color of the hydrated copper compounds in minutes from deep blue to the pure greenish blue color shown here </p><p><a href="http://en.wikipedia.org/wiki/Copper%28II%29_carbonate" target="_blank" class="externalLink ProxyLink" data-proxy-href="http://en.wikipedia.org/wiki/Copper%28II%29_carbonate" rel="nofollow">http://en.wikipedia.org/wiki/Copper(II)_carbonate</a></p><p><br /></p><p>I have read personal communications from researchers who do identify copper carbonate&nbsp; as a component of verdigris on modern coins, and it seems most often to be hydrated.&nbsp; Ancient coins ( 2000 yrs or approx) have gone through significant weather changes ( google it) and usually variations in exposure to water as well as temp changes. Lower consistent heat over 100s or thousands of years can cause the same loss of hydration as in the lab at higher heat/faster time. If the indigenous Indians in my area had utilized copper coinage for 2000 years, I would expect to find similar corrosion ( verdigris/bronze disease ) as in the middle east/Mediterranean area.</p><p><br /></p><p>BD is not a disease. Doug&#039;s explanation is good,&nbsp; as any chemical left will serve as an addition point for further reaction. I am not an ancient collector, but I would suspect the mixing of the metal was not as accurate as in modern coins. Thus an area of the metal which was more reactive would be a foci of corrosion and any recurrent effect.</p><p><br /></p><p>Now cleaning of &#039;BD&#039; seems to be legitimate for ancients, and if I did it, I would try some of the modern conservation chemicals such as Bad Thad&#039;s&nbsp; Verdi-care and protect the coin in a hard plastic or non-PVC flip with a dessicated storage area. I predict BD would not re-occur. IMO. I have not used Verdi-care on ancients, but I have on modern.</p><p>Chemicals to cause toning or etching ( acids) would be the opposite of what one should do for BD/corrosion .[/QUOTE]</p><p><br /></p>

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