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<p>[QUOTE=&quot;Roerbakmix, post: 4514417, member: 100731&quot;]Well here is an educated guess: since the blueish patina was in fact a rather thin layer of silver sulfide, artificially applied to the coin in higher concentrations than coins that tone naturally, the process of Ag + S &gt;&gt; Ag2S was probably still ongoing - and likely way faster than other coins that tone naturally. As [USER=101607]@shanxi[/USER] points out above, thin layers are blueish, and thicker layers become grey to black. </p><p><br /></p><p>Now lets focus on the coin:</p><p><img src="https://www.cointalk.com/attachments/hadrian-egypt-jpg-version-jpg.1118278/" class="bbCodeImage wysiwygImage" alt="" unselectable="on" /></p><p>Although I obviously didn&#039;t see the coin in hand, the blue patina is most profound under the legend AEGYPTOS on the reverse (9-12 &#039;o clock), and a bit on the bust - the other area&#039;s are greyish. So we have a blue thin layer on the bust and on the reverse, with thicker grey layers on other area&#039;s.</p><p><br /></p><p>Now with progression of time, your coin turned grey more homogeneously - this below is your coin (I&#039;ve edited your images a bit)</p><p>[ATTACH=full]1118535[/ATTACH]</p><p>The layers that were gray or only slightly blue (the thicker layers) became thicker due to the process of artificial toning that was still ongoing, while the area&#039;s that were more iridescent blue are almost &#039;done&#039;. </p><p><br /></p><p>Now a short note on the redox reaction described above, and the effect on ancient coins. In my experience, silver sulfide (i.e. the patina that most collectors &#039;want&#039; on a coin) starts in the more grainy, (microscopically) pitted area&#039;s. The redox reaction strips the silver sulfide, and exposes the underlying surface. Also, with the removal of silver sulfide, one does not only remove the sulfide, but also the silver (...). </p><p><br /></p><p>I&#039;ve magnified your &#039;before&#039; and &#039;after&#039;. Now this may well be overinterpretation, or due to differences in lighting, but this is the effect of the redox reaction that I meant above (and the reason I usually use other chemical methods):</p><p>Before: </p><p>[ATTACH=full]1118540[/ATTACH]After: </p><p>[ATTACH=full]1118541[/ATTACH][/QUOTE]</p><p><br /></p>

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