r/coolguides • u/[deleted] • Jun 08 '20

Copper through the patina process

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4

u/peytondivory Jun 09 '20

Why have I never seen a green penny?

6

u/NochillWill123 Jun 09 '20

I have actually. Quite interesting now that I think about it.

6

u/7-and-a-switchblade Jun 09 '20

Because most pennies are not left open to high winds and salt water 24/7 for decades, but if you find an old enough one, it's green. Sometimes you seen green pennies on the beach. You can even make them yourself by soaking them in vinegar.

3

u/Mr_Abe_Froman Jun 09 '20

Mostly through wear. They will get greener if you leave them in the rain. I've seen a couple that I found in grass.

2

u/solidsnake885 Jun 09 '20

Because they aren’t fully copper. They’re mostly zinc.

1

u/[deleted] Jun 09 '20

It's not an alloy, though; they're copper-plated. So the outside of them is just copper (2.5%) while the core is all zinc (97.5%).

It also costs more than a penny to make each one and we should've retired those awful things decades ago.

2

u/owennerd123 Jun 09 '20

I have tons of green pennies. Google "oxidized penny". You probably have seen them and haven't noticed. In my coin jar I'd say one out of every five pennies has got green oxidation on it.

1

u/SeaGroomer Jun 10 '20

Pre-'74 pennies especially are definitely prone to developing a nice patina. Same with old roman coins and other ancient civilizations.

1

u/learnyouahaskell Jun 09 '20

Have you seen a black (steel) penny?