Black crusty stuff

[SteveAZ]

I have been told and read that soaking in olive oil for a few days and then gently using a toothpick and the stuff comes off. I haven't tried it yet. I would wait for someone else to say thats correct before doing it though.

Steve

[Robert]

My guess is copper sulfide (CuS).

The environments the coin was in these many years makes all the difference. That's why some coins are "pristine" and others tarnished. The nice copper-colored bust and date are that way due to mechanical abrasion (wear). Without that wear, the whole coin would be evenly black.

If you *really* want to know, you could have it tested in an environmental lab. They'd need to squirt a drop of acid on an inconspicuous place and rub it with a Q-tip. But I bet they'd find mostly CuS.

[Bob P]

I have a collection of old Roman, Greek and Byzantine coins that had that hard crusty stuff all over them, and I was able to clean most of them with an olive oil bath. The best advice I can give when using this method is to be patient. I would start by letting it soak for 5-7 days and see if it begins softening that crud. If it does, then please be careful when removing it so you don't scratch the coin. I have used green thorns to carefully pick away any loose debris. They don't tend to scratch at all. All I did to be able to better control the thorn (especially if you have big fingers) was to hot glue the thorn to the end of a toothpick. This enable you to contol it more precisely with the new handle yo've made for it.
It may take longer for the oil to start working. Of course, there is always the possibility that it will not work at all. I have a few that I have had to leave alone.

[coop]

I would think Mineral Oil would be better than Olive Oil. Oilve oil is organic and can spoil in time. Not a good thing to happen to your coins. It was popular in the 60's (If you think you temember those years, you weren't there!) and some oldtimes still use it. But mineral oil is more like the type of oil used in the mintimg process with out the rotting smell of olive oiled coins. As far as the time it takes to get oil to work? The coin has been around this long and oil bath can be enjoyed while it is waiting for more time to go by. JMOHO