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Showerthought: people keep calling green corrosion on old coins "patina" when it's usually just bronze disease eating the coin alive
I picked up a Roman antoninianus from a guy at a flea market in Springfield last month for $8, and he kept going on about the beautiful green patina on it. I didn't say anything, but I've seen enough pitted coins by now to know that powdery light green stuff is not patina, it's bronze disease, and it spreads and keeps eating the metal until the coin is basically a crusty shell. Real patina is the dark brown or smooth green layer that formed over centuries and is stable, but the chalky bright green spots mean chlorides got in and there's an active chemical reaction going. I found out the hard way about 2 years ago when I threw a dug coin in a flip with my good ones and a few months later two of them had little green spots too. Now I keep a jar of sodium sesquicarbonate and soak anything suspicious for a few weeks, then dry it real careful, because once it starts it does not quit on its own. The guy at the market probably had 30 coins in that case and I bet half of them had it and he had no clue. Has anyone else dealt with bronze disease on a find, and do you soak right when you dig it or wait until you see the powder show up?
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