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<p>[QUOTE=&quot;desertgem, post: 1804508, member: 15199&quot;]Perhaps the terminology ~ verdigris, bronze disease, patina, corrosion , adds to the confusion. Assuming we are speaking of copper alloy coins and not silver, they can all apply, and relate to the formation of a chemical compound of the copper and an anion that can vary from sulfide, carbonate, oxide, etc.&nbsp; Many of these compounds can be a different color if hydrated (water added), For example copper(II) sulfate is slight greenish white, but when each molecule is hydrated with 5 water molecules&nbsp; ( copper(II) sulfate&nbsp; penthydrate ) it is a deep blue which we recognize&nbsp; &#039;colloquially &#039; as Copper Sulfate. So you can have many color, many physical structures ( crystals) , many different reactions on these coins ( even the same coins) . For instant, Copper Carbonate is more green, copper sulfate more blue,&nbsp; copper oxide reddish, copper sulfide blackish.</p><p><br /></p><p>But ( sorry Chris) they all involve the reaction with the copper of the coin, so is a % of corrosive action on the metal. Microscopic layers will be invisible, but the more the _______________( add any of the terms, in first line), the more damage to the coin.</p><p><br /></p><p>Jim[/QUOTE]</p><p><br /></p>

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