If anyone was following the Seleucid lots at the recent Leu auction back in May, you may have seen some with pretty heavy "coppery" deposits on some otherwise harshly cleaned coins. I was fortunate to win one of these and had a go at removing the deposits. My process was to use ammonium thisoulfate (AT) and toothpicks. I was mostly banking on this either not working at all (i.e. doing no harm) or helping remove some of the deposits, I didn't expect I'd remove it all since these are apparently copper and not horn silver. I mixed a 10% solution of AT with water by weight and would soak the coin for 1-3 minutes before rinsing it off and using toothpicks to dislodge anything loose. In the end it took about 2 hours of cleaning and 5 or 6 baths in the solution. If I couldn't remove the copper, I was hoping at least to dull the shiny surface. This was by far the shiniest coin I have ever received and it was not due to having any lustre. In my experience, AT will leave a dark, dull, film on the surface of a coin that can be easily removed with light rubbing but even when removed the surface typically does lose its shine. Oddly enough, in this instance I also saw yellow "toning" in places where there was previously neither toning or copper deposits. This can be removed easily but for now I'm leaving it as it gives the coin an "old cabinet toning" look. Before: After:
