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<p>[QUOTE=&quot;desertgem, post: 1513506, member: 15199&quot;]The use of the term &quot;Carbon &quot; spot probably confuses the novice and they think they really are related to carbon. </p><p><br /></p><p>They are not. </p><p><br /></p><p>They are areas of Copper sulfide deposits, ~ Corrosion.&nbsp; Copper sulfides produce a dark brown to black corrosion on the coin surface with Hydrogen sulfide gas being a good source.&nbsp; Storage with vulcanized rubber products such as rubber bands, some shoe soles, toy cars with rubber wheels, etc.&nbsp; This process is what in environmental gases can cause a copper cent to become steel grey and even black over the years. In thin films they can contribute to toning, but the normal corrosion colors of copper are produced by sulfates and carbonates, which are more blue-green in color, but it the same. </p><p><br /></p><p>Coin doctors often use Hydrogen sulfide gas in a mixture to produce AT effects, but a mix stronger to the sulfide side of the mix usually produces a dark coin that isn&#039;t commercially acceptable. IMO.[/QUOTE]</p><p><br /></p>

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