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<p>[QUOTE=&quot;Roerbakmix, post: 3817360, member: 100731&quot;]Some of you probably know I&#039;ve been working on different techniques to restore ancient coins with horn silver. I&#039;m working on my PhD as well, and have to prioritize things, so it will take some time.</p><p><br /></p><p>However, this fun time lapse of a Sev-Alex denarius with black horn silver is too fun (and cool, imho) not to share:</p><p>(nb: the GIF takes 5.2 second, and then restarts)</p><p>[ATTACH=full]1016836[/ATTACH]</p><p>50 ml of distilled water with two tablespoons of sodium thiosulphate at warm temperature (usually I will warm until boiling, but as the camera lens became condensed, I had to use a lower temperature). The time lapse (5 seconds) took like 10 minutes in reality.</p><p><br /></p><p>Horn silver, or silver chloride (or bromide, or a combination) reacts with sodium thiosulphate as following:</p><p>AgCl + 2Na2S2O3 → Na3[Ag(S2O3)2] + NaCl</p><p><br /></p><p>Usually, the coin will turn black (which was eventually also the case here, but not present in the video, as the reaction was considerable slower due to the lower temperature). This can easily be removed by either rubbing the coin between finger and thumb under flowing water, or using a mild abrasive such as baking soda.</p><p><br /></p><p>Sodium thiosulphate does not react with silver or copper, and will subsequently not <i>cause</i> pitting. However, the horn silver is (not in all cases) essentially a form of corrosion of the coin, so beneath the layer of horn silver, pitting may be present. There are various ways to determine this beforehand, which I&#039;ve posted on other threads. My intend however is to write a comprehensive overview and guide on the restoration of horn silver.[/QUOTE]</p><p><br /></p>

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