TIL old coins turn dark in certain dirt types

I used to just rinse off any coins I found with water and call it good. But after I dug up a 1910 Indian Head penny near an old barn site in Ohio last month, I noticed it had this weird black crust that wouldn't scrub off. My buddy who's been doing this for like 20 years told me it's from high sulfur content in the soil around old manure piles. Now I soak them in distilled water for a few days before even touching them with a brush. It's way slower but I haven't messed up any details since. Has anyone else run into this with farm site finds?

2 comments

2 Comments

evannelson2mo ago

Nah, you're close but that "high sulfur content from manure piles" thing isn't quite right. It's more about the soil pH and how it reacts with the copper in the penny. Manure does change the soil chemistry but the black crust is usually from copper sulfide forming when the coin sits in acidic, oxygen-poor dirt for decades. I've dug up Indian Heads from old farm spots in Illinois that came out jet black but the soil around them was mostly clay and didn't even smell like sulfur. Your buddy probably meant the general dirt chemistry, not actual manure piles specifically.

derek_dixon782mo ago

Funny you mention that @evannelson because this happened to a buddy of mine up in Wisconsin. He pulled a 1909 VDB penny out of a cornfield that looked like it was painted black, and after soaking it in distilled water for a week the crust just flaked right off revealing a beautiful brown surface underneath. The soil there was super sandy and dry, nothing like manure or clay, so it really does seem to be more about the general chemistry like you're saying. Have you ever had any luck with using a peroxide bath on those black crust pieces or do you stick with just water?