TIL the crusty green stuff on old copper coins is NOT always patina, and I scraped $40 off a 1700s half penny

Andrew Kelly · 2026-10-13T10:40:04.08702+00:00

I used to think any green coating on old copper meant real age, so I left it alone or even bragged about it. Then a guy at a coin show in Allentown pointed out that bronze disease is a powdery light green that keeps spreading, unlike stable dark patina, and my 1736 half penny had it bad. I tried a toothpick and some distilled water on a junk coin first, and it kept flaking for two weeks straight. So how do you all tell the two apart before you touch anything, or do you just leave every green coin alone?

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TIL the crusty green stuff on old copper coins is NOT always patina, and I scraped $40 off a 1700s half penny | Ancient Coin Finds - Topic Shares