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<p>[QUOTE=&quot;Roerbakmix, post: 3909382, member: 100731&quot;]So this Septimius Severus denarius had some dark spots, which I ID&#039;d as a combination of horn silver (silver chloride/bromide) and copper.</p><p>[ATTACH=full]1030372[/ATTACH]</p><p>After soaking the coin for 5 minutes in a solution of distilled water sodium thiosulphate, followed by 5 minutes in a solution of distilled water and purified citric acid, the coin looks as follows:</p><p>[ATTACH=full]1030373[/ATTACH]</p><p>Both photo&#039;s were taken with exactly the same photosettings (ISO 100, F22, 2 sec), which is my default setting, with no post-editing apart from cropping.</p><p>I was pleasantly surprised to see that the detail of the lettering improved as well, likely because of a very thin layer of horn silver on the entire coin. </p><p><br /></p><p>The mild yellow tone that is visible is due to using the same solution of sodium thiosulphate for a bit to long, causing the sodiumthiosulphate to break down in sulphate, which is yellow. This can easily be removed, but &#039;in hand&#039;, it&#039;s not visible.</p><p><br /></p><p>Please note that removing copper (or iron) depositions requires the coin to be of relatively high silver purity, else pitting may occur. Sodium thiosulphate is inert to silver.[/QUOTE]</p><p><br /></p>

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