Numismatic and History Discussion Forums > Uncleaned Ancient Coin Discussion Forum

Cleaning crusty zinc coins

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SC:
Anyone have any experience in cleaning zinc coins?

I have searched the forum but have't found any old messages.

I am looking at ways to clean 17th-18th century Vietnamese zinc cash.  These are coins were made of almost pure zinc, not a Zn-Cu alloy.

They often have a thick beige/tan coating on part or all of their surface that looks just like hardened clay but is much harder.  I believe that it must be some sort of mineralized adhesion.  

Given that zinc is very soft it makes mechanical cleaning perilous - the adhesions are harder than the base metal.

SC

PS  I have found lots of advice for cleaning "modern" zinc coins which have small deposits of small bits of powdery white "zinc-disease" on them.  What I am looking for is different - cleaning tough thick crusts of zinc.

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