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<p>[QUOTE=&quot;ptHoneyBadger, post: 4061528, member: 110356&quot;]I have seen some blue/purple color on copper that I thought looked like NT. I suspect this develops over an extended period of time from prolonged exposure to some unknown substance in the coin&#039;s local environment. Obviously, however, the most common type of oxidation we see on copper alloy coins is the brown to black copper oxide.</p><p><br /></p><p>This is an informative article on copper reactivity.</p><p><a href="https://copperalliance.org.uk/knowledge-base/education/education-resources/copper-reactivity-patination/" target="_blank" class="externalLink ProxyLink" data-proxy-href="https://copperalliance.org.uk/knowledge-base/education/education-resources/copper-reactivity-patination/" rel="nofollow">https://copperalliance.org.uk/knowledge-base/education/education-resources/copper-reactivity-patination/</a></p><p><br /></p><p>I have wondered if the &quot;unnatural&quot; blue/purple seen from things like MS70 isn&#039;t more related to the particular alloy of the coin. It seems that the areas that take on the most color are the areas that were a darker brown to start. If the degree of copper oxide formation in these areas is more pronounced, and the MS70 somehow washes away the oxidized copper, would not the remaining tin and zinc in the alloy be more visible giving a blue/purple color as light is refracted from the coin?</p><p><br /></p><p>Although the ratios of Cu, Sn, and Zn in small cents has remained fairly constant (with some notable changes), surely there have been major differences in the billions of alloyed planchets manufactured over the years. This could certainly account for the unpredictable results people describe when copper alloy coins are exposed to any chemical that alters its oxidized surface.</p><p><br /></p><p>JMO[/QUOTE]</p><p><br /></p>

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