Metal finishing Q&As since 1989

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Electrolytic cleaning of Silver Jewelry & Coins

Q. How can I "polish" silver jewelry using electrolysis? There is a lot of crevices in them that I am unable to clean well with the isothiocyanate paste they sell in jewelry store.

M.Tata
- Phoenix, Arizona
2003

Q. After reading a museum website detailing the electrolytic cleaning of silver artifacts, I decided to give it a try on one of my silver dollars.

The dollar was pretty badly tarnished. I tried using the aluminum foil and baking soda trick and it didn't really work well. Reading the other posts, I think it's probably because I'm in California and didn't use any water softener.

Anyway, I find electrolysis fun so it was fine to have an excuse to try it. I mixed a 10% sodium hydroxide [liquid caustic soda in bulk on Amazon] solution with distilled water. My cathode was a harness I made from copper wire and my anode was a strip of platinum. I cleaned the coin with dishwashing liquid, acetone [on eBay or Amazon], and distilled water (I was wearing nitrile gloves [on eBay or Amazon] when I was handling the coin, I don't know if that makes a difference). I put the coin in the harness and lowered it into the solution.

The article on the museum website said a coin could take several hours so I left it in there and went about my business. When I checked it again the black tarnish was gone but the coin was yellow. I threw out the lye solution and mixed up a fresh batch. I tried the electrolysis again but the coin stayed yellow.

On a hunch, I put it in vinegar after cleaning and rinsing it and the yellow disappeared! The coin looked totally shiny and white.

So my question is, what was the yellow stuff?

Ray Avedian
Santa Monica, California, USA May 19, 2012


1923 Silver Dollars on eBay

Q The article was here, in case anyone is interested:

http://nautarch.tamu.edu/CRL/conservationmanual/File13.htm ⇩

I get the science behind it. That's why the yellowish deposit on the coin was so perplexing. It sounds like it could have been silver sulfide, what with the color and the way that it came off in acid, but I don't see how sulfur can oxidize the silver while it's a cathode. Not too important, just was curious.

Ray Avedian [returning]
- Santa Monica, California, USA

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