I recently acquired this Ptolemy VI tetradrachm and currently am trying to figure out if it can be improved. I am mainly interested in cleaning the reverse if at all possible, but I am having a difficult time determining if the black stuff happens to be hard dirt/crud or horn silver. If its horn silver then I'll leave alone. Part of the reverse is free of encrustations so its possible the black is horn silver that the original person could not remove. But the texture looks a lot more "dirt-like", I guess, which makes me think it could be dirt. I rubbed a portion of the black area with a q-tip just to be safe, but nothing came off. Thanks for any help!
To me looks like horn silver and dirt. I think the best you could do is lighten the surface. It is a nice coin as is.
It is horn silver. I think it looks okay as-is but you might be able to get rid of the horn silver... @Roerbakmix appears to be our resident horn silver cleaning expert. Paging Dr. Roerbakmix stat!
Thanks @TIF for the compliment I agree with above: this looks like horn silver (search on CT for my previous post on Horn Silver for more information on it). I would be very hesitant to clean it for two reasons: 1) it looks like it was cleaned before, with some unfavorable results (mainly on the obverse). Horn silver, in my experience, comes in different forms. This type, the diffuse granular type, is difficult to treat. My hypothesis is that the horn silver in these cases is caused by corrosion of the coin itself (in contrast to horn silver deposits from other coins, e.g. as can be found in coin hoards). The corrosion is often masked by a layer of horn silver, but becomes visible when the horn silver is dissolved. 2) the metal on the obverse shows signs of this corrosion, and cleaning the whole coin will probably worsen the appearance. However, the reverse shows solid and good silver, and would probably improve. I would try to do the following: 1) create a strong solution of sodium thiosulphate in distilled water (e.g. 10 grams/50 ml) 2) heat this until cooking point 3) on the reverse, apply a few drops in an area with a thin layer of horn silver (e.g. near the "LKB" legend. 4) wait a few minutes, remove the solution, and repeat. 5) after 10-15 minutes, throw away the solution, and make a new solution. Sodium thiosulphate degenerates over time into, among others, sulfur, which can result in a yellow-grey patina. I expect the horn silver to change appearance (it changes colour, becomes yellow, and a bit translucent) and then dissolve. The smooth metal on the reverse is a good sign. Hope this helps! Feel free to pm me.
At last a sensible comment on horn silver! Yes – the key question is - does the silver in the AgCl derive from the host coin – in which case the host coin is already damaged underneath, OR, does all the horn silver derive from some adjacent coin buried close by, in which case cleaning is a good idea. So the key question is not - how to clean - but - if to clean. I have been paid good money in the past for my opinion, but here is a freeby in this case – leave it alone. @Roerbakmix is also right to point out - if you mess up during cleaning you will get a nasty yellow stain that is hard to shift Rob T PS still waiting for a comment on coin weight standards that deserves praise sigh
Really appreciate all the feedback, thank you. @Roerbakmix thanks for your step by step process as well. Since you are knowledgeable about removing horn silver and would be hesitant to clean this one then I’d rather leave my coin alone. But what about ammonia? Any idea if it could have an impact on the horn silver? Also, recently found this horn silver cleaning solution online. Has anyone here tried this out before? https://nobleromancoins.com/product_reviews.php?products_id=976
Is this drachm (Price_1379; attributed to Antigonos Monophthalmos) also horn silver? I was told it was fire damage, but after reading this thread and viewing the images I doubt the fire theory. Also, does it seems odd that there seems to be a distinct line on the reverse at which the dark surface (whatever it is) begins? Many thanks in advance for any information!
Although both AgCl and AgBr dissolve in ammonium, cupper will also react quickly, making this method unsuitable for bullion coins or fourrée. Although I’ve tried this method a few times, the results were not as favourable as sodium thiousulphate. Generally, the solution should be at a concentration of ca. 5%. This sure looks like horn silver. The diagonal line (clean/horn silver) is intriguing. The obverse shows the same line: Maybe it was partly submerged in a cleaning solution? I would (given the appearance of the cleaned part) definitely soak this one in sodium thiousulphate. I've posted this before (it's from my still unfinished guide on restoring horn silver on ancient coins): THis is the same 'patchy' layer of horn silver and the effect of sodium thiosulphate.
Nope - just what happened to it in the ground. Very typical. It has been cleaned using a reagent (weak acid probably) which took off the copper salts or whatever - but did not shift the horn silver.
