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<p>[QUOTE="hotwheelsearl, post: 7910574, member: 75143"]I tend to leave coins in NaOH for 5-8 hours, basically overnight.</p><p><br /></p><p>You can 100% leave them in for too long. Initially it tends not to impact the coin much, but after too long it can leave them pitted and rough.</p><p><br /></p><p>It can also change the color from green to a brownish color.</p><p><br /></p><p>Trajan Decius. It was encrusted, and artificially run through a rock tumbler. It was initially green.</p><p>[ATTACH=full]1365761[/ATTACH] </p><p>I left this in NaOH for about 8 hours, and ended up with this:</p><p>[ATTACH=full]1365760[/ATTACH] </p><p>The color changed significantly, but it removed nearly all of the encrustations without any major impact on the surfaces of the actual coin.</p><p><br /></p><p><br /></p><p>The main problem is if the coin has an original greenish patina, it will 100% be removed.</p><p>[ATTACH=full]1365763[/ATTACH] </p><p>This had a nice dark green patina, but the encrustation would never have been removable mechanically.</p><p>[ATTACH=full]1365762[/ATTACH] </p><p>This took about 12 hours in NaOH. The color became brown, and the surfaces got a bit rough. </p><p><br /></p><p>Something to note, however: if a surface becomes rough after chemical treatment, it usually means that the encrustation or corrosion <i>had already impacted the surface</i>. Basically, nothing could have been done to prevent surface roughness on some of these coins.</p><p><br /></p><p><br /></p><p>Sometimes, the host coin is just too far gone and there's nothing to be done.</p><p><br /></p><p>This Trajan had a host of minerals. The minerals were rough, there was no patina to speak of.</p><p>[ATTACH=full]1365764[/ATTACH] </p><p><br /></p><p>Cleaning involved NaOH, sodium thiosulfate, and acetic acid. The chemicals cleaned off the minerals, revealing the originally poor surface. However, in this case it restored the original yellow orichalcum color.</p><p>[ATTACH=full]1365765[/ATTACH] </p><p><br /></p><p><br /></p><p>Basically, NaOH is my best friend. You may sacrifice some patina, but you can make up for it in overall details.</p><p><br /></p><p><br /></p><p><br /></p><p>Here;s an example of purely mechanical cleaning.</p><p><br /></p><p>The encrustations appeared to be rather fragile, so I opted for a mechanical attack with distilled water soaks.</p><p><br /></p><p>[ATTACH=full]1365768[/ATTACH] </p><p><br /></p><p>I saw a lovely green patina underneath, which is why I didn't subject it to chemicals.</p><p>However, the surfaces are kinda rough despite my best efforts. At this point its a judgment call whether to lose the green patina in favor of brown, or to live with a very rough surface.</p><p>[ATTACH=full]1365767[/ATTACH][/QUOTE]</p><p><br /></p>
[QUOTE="hotwheelsearl, post: 7910574, member: 75143"]I tend to leave coins in NaOH for 5-8 hours, basically overnight. You can 100% leave them in for too long. Initially it tends not to impact the coin much, but after too long it can leave them pitted and rough. It can also change the color from green to a brownish color. Trajan Decius. It was encrusted, and artificially run through a rock tumbler. It was initially green. [ATTACH=full]1365761[/ATTACH] I left this in NaOH for about 8 hours, and ended up with this: [ATTACH=full]1365760[/ATTACH] The color changed significantly, but it removed nearly all of the encrustations without any major impact on the surfaces of the actual coin. The main problem is if the coin has an original greenish patina, it will 100% be removed. [ATTACH=full]1365763[/ATTACH] This had a nice dark green patina, but the encrustation would never have been removable mechanically. [ATTACH=full]1365762[/ATTACH] This took about 12 hours in NaOH. The color became brown, and the surfaces got a bit rough. Something to note, however: if a surface becomes rough after chemical treatment, it usually means that the encrustation or corrosion [I]had already impacted the surface[/I]. Basically, nothing could have been done to prevent surface roughness on some of these coins. Sometimes, the host coin is just too far gone and there's nothing to be done. This Trajan had a host of minerals. The minerals were rough, there was no patina to speak of. [ATTACH=full]1365764[/ATTACH] Cleaning involved NaOH, sodium thiosulfate, and acetic acid. The chemicals cleaned off the minerals, revealing the originally poor surface. However, in this case it restored the original yellow orichalcum color. [ATTACH=full]1365765[/ATTACH] Basically, NaOH is my best friend. You may sacrifice some patina, but you can make up for it in overall details. Here;s an example of purely mechanical cleaning. The encrustations appeared to be rather fragile, so I opted for a mechanical attack with distilled water soaks. [ATTACH=full]1365768[/ATTACH] I saw a lovely green patina underneath, which is why I didn't subject it to chemicals. However, the surfaces are kinda rough despite my best efforts. At this point its a judgment call whether to lose the green patina in favor of brown, or to live with a very rough surface. [ATTACH=full]1365767[/ATTACH][/QUOTE]
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