What turns a penny brown?

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OK Doug, sure. Just to remind you....

Direct quotes:

CoinTalk member: "Does oxygen always have to be part of the mix in order for a coin to tone?"

@GDJMSP : "In simple terms, yes"

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While oxidation of copper surfaces is indeed "corrosion" by definition - copper collectors should rest easy because when copper oxidizes it creates a protective barrier on the surface to prevent further oxidation. Thus, brown evenly toned copper is a much safer and much more stable type of copper to collect.

I've always said collecting RED copper is a foolish thing long term - eventually all copper will turn brown. The benefit of purchasing a copper coin after it has already oxidized is that you know it will not likely have unsightly, uneven blotchy toning. This instability of copper's red color is the very reason the TPGs stopped guaranteeing the color designations of copper coins.

This thread needs more pictures:

 

Thanks for the update GD. Be safe

 

Let's have more fun. Place your oxygenless air and copper penny in an environment at high pressure and temperature and the copper will react with the nitrogen present (as the largest component of air). I mean, really high pressure and temps, but it would tone...

 

I would reply that under normal circumstances it is unlikely to find 'air' devoid of oxygen, so hitting that state is then less of a jump to further theoretical extrapolation in my mind.

I wasn't trying to insult.

Perhaps people could store their coins in a vacuum or inert gas?

 

I say let 'em develop a patina! They'll look great in 2000 years!

 

Actually "air devoid of oxygen" or at least with the oxygen reduced, is not rare at all. I see the advice for people to put a few shiny penn... cents in along with their silver coins to scavenge the oxygen in the air in the container.

 

You stated unequivocally that it was called oxidation because oxygen was involved. That is false. It’s called oxidation because of electron loss.

Yes, under normal circumstances, oxygen is the driver for toning of coins. I never implied that fluorine was a driver. I brought up fluorine (and other elements) to prove my point that it is NOT called oxidation because of oxygen. Fluorine is an oxidizer, and is not oxygen.

 

Oh, stop. Of course it's called oxidation because of oxygen! Oxygen was discovered by Joseph Priestly and investigated by Antoine Lavoisier in the 1700's. At that time they didn't know an electron from an elephant.

 

Can you read? Just because something was named something because of ignorance 300 years ago doesn’t mean its definition is the same today.

I said oxidation does not imply oxygen. Not the reverse.

 

Swallow a red penny guaranteed it’ll come out brown lol