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<p>[QUOTE=&quot;Roerbakmix, post: 3787867, member: 100731&quot;]Thanks [USER=56859]@TIF[/USER]. I agree: it sure looks like horn silver. As mentioned before, I&#039;m in the process of writing a detailed guide on the restoration of coins with horn silver, but my 1.5y/o twin in combination with finishing my PhD is not really beneficial this. Anyway, here is a similar example of horn silver on a Sev. Alex denarius:</p><p>[ATTACH=full]1011527[/ATTACH]</p><p><br /></p><p>And below a timelaps of the same coin in a solution of sodium thiosulphate.</p><p><br /></p><p>[ATTACH=full]1011528[/ATTACH]</p><p><br /></p><p>Your coin has been cleaned before, both mechanically and chemically as can be seen by the scratches (mechanical):</p><p>[ATTACH=full]1011529[/ATTACH]</p><p>... and the somewhat porous appearance of the silver that was beneath the horn silver. It was probably treated with an acid, which is not very effective on horn silver. Sodium thiosulphate however, is.</p><p><br /></p><p>I&#039;ll copy paste my cleaning steps for horn silver below:</p><p><br /></p><p><b>Chemical cleaning </b></p><p><br /></p><p>Probably the easiest and safest method to remove horn silver is by using a solution of sodium thiosulphate (2Na2S2O3). Both AgCl and AgBr dissolve in sodium thiosulphate, as can be seen from the following reactions:</p><p><br /></p><p>§&nbsp; Silver chloride (AgCl): AgCl + 2Na2S2O3 → Na3[Ag(S2O3)2] + NaCl</p><p><br /></p><p>§&nbsp; Silver bromide (AgBr): AgBr + 2Na2S2O3 → Na3[Ag(S2O3)2] + NaBr</p><p><br /></p><p>The elemental silver will not dissolve. The 2Na2S2O3 will cause a similar blackish patina as silver sulphate, however this is less stable and can be easily removed using a piece of cloth. Generally, all types of horn silver can be treated using this method.</p><p><br /></p><ol> <li>Create a solution of distilled water. Use 2 grams (ca one teaspoon) of sodium thiosulphate per 100 ml water. Generally, 100 ml should be enough for a medium sized coin.</li> <li>Warm the solution to a lukewarm temperature (ca. 30-50c).</li> <li>Gently place the coin in the solution. The reaction begins immediately, and is different depending on the type of horn silver:</li> </ol><p> <ul> <li>Type 1 (black spots) and 3 (waxy layer)&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <ul> <li>Gradually, the coin turns black. This is because of the 2Na2S2O3, which is part of the reaction.</li> <li>In 10-30 minutes, depending on the severity of the horn silver, the horn silver will dissolve.</li> </ul></li> <li>Type 2 (metal deposits) and 4 (encrustation):&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <ul> <li>First, the type 2 (metal deposits) and 4 (encrustation) will turn yellow (after 10-20 sec)</li> <li>Second, the silver that is exposed to the sodium thiosulphate will turn darker and black eventually (20 sec until end of procedure)</li> </ul></li> </ul><p>4. Remove the coin from the solution, using a spoon, and rinse it using tap water. If the horn silver has been dissolved completely, a brief mechanical cleaning of the 2Na2S2O3 can be done using a paste baking soda NaHCO3 with a droplet of water can be used. If the horn silver has not been dissolved, repeat from step 1.[/QUOTE]</p><p><br /></p>

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