Numismatic and History Discussions > Uncleaned Ancient Coin Discussion

How to Clean Silver (not Silvered) Coins

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Miguel Diaz:
I've used 2-3 times acid formic to remove green on Antonines denarii.

After some seconds, green is removed ... Then you must place the coin in distilled water to stop the acid.

Green is removed. If coin contains a significant proportion of copper, he will be darker, with a pretty good patina and spot where green was will be a little lighter than the rest of the coin.

If coin has a lot of silver, then the spot where green was will be darker or black like normal silver oxydation.

My method work with coins with silver, a lot of content of silver.

Miguel Diaz:
I've heard that some green could come from reaction of plastic. And that acetone could remove it. I will try this one of these days to verify this ...

A note about "Horn Silver". Horn silver is a silver chloride compund, tha tis formed in a similar fasion to tinchloride in Bronze Disease. You could call it silver disease. It is not water soulable and hard to treat, but like BD, it will ruin good coins.

   The best method I have found for it, and the simplist, is the use of photographic fixer.
Most fixers are based on the thiosulfate ion, especially ammonium thiosulfate. Up until the 1970s, sodium thiosulfate or 'hypo' was the commonly used fixer. Both fixers work best in acid conditions and this is usually created using small quantities of acetic acid. The fixer removes the unexposed silver halide [in this case AgCL or silver chloride] leaving behind the reduced metallic silver. It takes a small amount, and a soak of 30 minutes should be sufficient. Soaking and scrubbing afrewards is recommended, especially the soaking in distilled water, to remove any remaing salts.


Any other methods I can try for horn silver?? Photographic fixer may be a bit of a hassle for me to get my hands on.

Formic acid is seriously nasty, and I wouldn't trust anything so powerful as to take it off in seconds. If you want to use acid, short soaks in white vinegar, interspersed with brushing, will do it slowly and safely.


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