Message:

<p>[QUOTE=&quot;desertgem, post: 3055285, member: 15199&quot;]It is a reaction to the copper. Some are of the opinion that it must be CuO deposits, as that is a dark black compound. Others claim it is a sulfuration of the copper surface to CuS ( also a black material). If you have some chemistry background, read the wikipedia articles on these 2 compounds and then try this article , which is about as close to working with the surface of a copper coin ( silver would be similar in the process) but they used a thin film material to isolate results better.</p><p><br /></p><p><a href="https://www.hindawi.com/journals/ijp/2009/304308/" target="_blank" class="externalLink ProxyLink" data-proxy-href="https://www.hindawi.com/journals/ijp/2009/304308/" rel="nofollow">https://www.hindawi.com/journals/ijp/2009/304308/</a></p><p><br /></p><p>The result part here is interesting:</p><p><i>During formation of the layer on the surface of polycaproamide, all processes proceed in an open medium; therefore, <span style="color: #ff0000">it is not possible to avoid ambient effects. Since the surface of this layer is active, it adsorbs oxygen, water, and other contaminants</span></i><span style="color: #ff0000">.</span></p><p><br /></p><p>substitute &#039;coin surface &#039; for polycaproamide&#039; and you see that the reactive surface can adsorb things known to cause environmental damage to coins. They uses XRF and XPS to analyze the surface compounds. The bonding ( being partially metallic bonding ( Cu), and partially covalent with the sulfur and oxygen involved , they get ratios of&nbsp; Cu<font size="2">1.9375<font size="5">S&nbsp; rather the Cu<font size="3">2<font size="5">S we see most in chemistry. These ratios are found in some minerals that contaminate copper ore.&nbsp; </font></font></font></font></p><p><br /></p><p><font size="2"><font size="5"><font size="3"><font size="5">I think at this point that sulfuration of the copper surface occurs and then interact on environmental factors to cause black spots, which could be CuS alone , CuO, or combination. Certainly not carbon. I would hope others contribute, as this has been an argument for decades. Jim</font></font></font></font>[/QUOTE]</p><p><br /></p>

Your name or email address:

Do you already have an account?

• No, create an account now.
• Yes, my password is:
• Forgot your password?

Stay logged in