Ancient coins, by their very nature, have been around for a while. All sorts of things happen to them from the day they were minted to the day they enter our collections. Most were buried, intentionally or unintentionally, where they were subjected the effects of the elements, as well as the other coins in the hoard, if it is not an individual find. Horn silver is a common occurrence with silver coins. A couple of weeks ago this imitative tetradrachm from the late 5th to mid 4th centuries BC, arrived (dealer's photo). As can be seen there's a considerable layer of horn silver on the obverse. After over a week of cleaning, most of the horn silver is no longer present. The weight did decrease, from 16.7 grams to 16.34 grams today. There are some tradeoffs: the cleaning did expose porous surfaces, there is some loss of contrast, and graffiti on the reverse is now visible. But, in the area of the horn silver deposit, something else revealed itself. To the right of Athena's portrait, there appears to be a Phoenician or Aramaic Gimel: Otherwise, this coin is not very noteworthy. Given its condition I would imagine most TPG services wouldn't even bother to certify it. But, that is not the point. The point, instead, is the pleasure of collecting ancients that fit your bill. That's what collecting is all about. Have other CT member discovered new features of a coin as a result of horn silver removal and cleaning?
Well done with the cleaning. What method did you use? This is an interesting question. This probably counts as new features: after This one was fun: just a thick layer of mud. Wonder why the dealer didn't bother to clean it (it's a rather scarce coin) After a good rinse of water: One of the most dramatic restoration result is probably this one: removed the horn silver, only to find out a tiny spot of iron oxides on the reverse.
I used primarily sodium thiosulfate/thiosulphate (pentahydrate) 99% pure, mixed with distilled water and heated in my 750 watt microwave for about 40 seconds. I then stir the solution to make sure the tablets are totally dissolved. For this coin I applied the solution on the affected area with cotton swabs. I went through a lot of those. I would pause the removal and assess the coin for a day or two, and then resume until the process reaches the point that is acceptable for me: not total removal, with enough horn silver to provide some contrast as befits an ancient coin. The solution did remove deposits in other areas, which wasn't my intention, but the coin will tone down over time. Using sodium thiosulfate/thiosulphate has been a revaluation for me. In the past I would attempt to remove horn silver using naval jelly, but that was not as effective and the process did darken the treated coin in sometimes not a desirable way. The "waxy" horn silver is especially problematic using this approach. I really like the work you did with the posted coins, especially the first one. That must have been quite a chore.
