Discussion in 'Ancient Coins' started by Bing, Sep 21, 2015.
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Tetradrachm, Phoenicia - Arados, Year 181 = 79 - 78 BC
Ob.: turreted and veiled bust of Tyche, right
Rev.: ΑΡΑΔΙΩΝ, Nike standing left, holding aphlaston with right hand and palm with left, date ΔΠΡ, Phoenician letters, and MΣ to left, all within wreath.
I think @TIF may be right. I'm planning on cleaning a few coins with horn silver using sodium thiosulphite and write a sort of step by step identification and restoration guide on it.
Cleaning ancient coins is a debated topic, though for me, it adds a fun dimension to collecting them. Below an example of horn silver, and how I attempted to restore it (posted before).
Horn silver can present in many different ways. For example, this Meneander drachm (reverse):
Note the encrustations (the coin was cleaned quite aggresively before I bought it). As you can see, e.g. near the monogram (5 o'clock), the silver under the encrustations is smooth, which is a good sign.
After gently brushing with baking soda (as part of mechanical cleaning), the encrustation starts to shine (indicative of a metal deposit instead of dirt, i.e. likely horn silver)
The later stages. Here you can note two things: 1) indeed, neer the monogram, the silver below the encrustations is smooth and could be removed relatively easily. At the left, however, this is not the case, and there is some pitting.
2) the blackish tar-like residue, which is non-crystalized horn silver, which is very difficult to remove mechanically, but using aluminium and baking soda (i.e. redox reaction) did the trick quite well.
In the end, I did something incredibly stupid: trying to repatinate the coin with elemental sulphur (to create a silver sulphite patina instead of risking chlorides to damage the coin), I heated the coin to 180 C, while the melting point of sulphur is 115 C. This caused the sulphur to melt and react quite agressively with the coin (so don't do that).
In this case, you will of course end up with a shining, polished coin. However, in the case of your coin, I would reckon it would clean op quite well.
A very short immersion in a lukewarm citric acid solution (in distilled water) will do the coin no harm. Afterwards, deacidify the coin using distilled water for some time.
#Edit: I didn't notice the '2015' at the first post ...
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