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Does anyone know a good way to stop silver milled coins from tarnishing after cleaning? I recently found a William III sixpence in the river Thames, and after getting all of the crud off of it, it quickly tarnished to a dark grey. I have used an eraser several times to remove the tarnish, but it quickly re-appears. Would this be because it came from the Thames, and exposure to air has caused the tarnish? Any one got any ideas as to how to protect the coin, without damaging it or reducing it's collector value?
Thanks for any help
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Despite the Thames apparently being clean now (?) it certainly hasn't always been so. Who knows what chemicals that coin has been subjected to and in what concentrations.
My idea with the soaking in distilled water is that trace salts or minerals on the coin or in micro cracks can be leached out through osmosis in distilled water. The acetone soak would remove all remaining water even at the bottom of nano sized splits, cracks and scratches.
If none of the above works then you could maybe try renaissance wax or another product that sealed the coin from air without degrading it in any way...The tarnish will be an oxide residue that is initiated through contact with air...I don't know the silver content of WIII sixpences but that will also have a bearing on the tarnishing.
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The only way to prevent further oxidation on anything silver is to put it in a vacuum removing any air around it, but this isn't a practical way to store items.
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