Green spots on one cent piece

I have this 1975 Lincoln Memorial.
I noticed it has green spots on the top of the obverse side.
What can they be?
Is it dirt, corrosion,...?

 

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I can't really tell from your photo, but green usually equals copper salts, which means that the zinc plating has been penetrated and the Miracle of Modern Chemistry has begun. You can't reverse it, but you can stop it by keeping it very, very dry. Any humidity (atmospheric, heavy breathing, doggy licks, etc.) combined with good old oxygen (There was something in the air, that night, Fernando...) will reactivate the corrosion process.
There's also a possibility that it's organic, like a germ colony in a petri dish.

If you MUST clean it, try this Wash it *gently* in warm sudsy water. Use a Q-tip to dab at the spot only to avoid damaging the rest of the coin. Pat Dry it *completely and immediately* and see if the spot has thinned or reduced. **THIS IS A HIGH RISK PROCEDURE. YOU CAN DO EVERYTHING RIGHT AND STILL MANAGE TO DAMAGE THE COIN**. It's usually best to just let it be.

 

You left out a song reference. (Let it be, let it be, let it be, let it be, whisper words of wisdom, let it be)

 

Uh- 1975 is 95% copper.

 

Exactly. The zinc PLATING has been penetrated and oxidation has begun on the COPPER planchet.

 

Green spots are common in cents that have been poorly stored. You can remove them if you know what you are doing, but the damage is done. The coin will never be as it was before the spots started. A safe way to deal with it is to soak in acetone to dry it out and store in a dry environment. Luckily its a cheap coin, so if its for your collection just spend it and buy another.

Lol, sorry Koen, I forgot you cannot easily just get another. I am sure you will be able to obtain better examples in the future sir. THese are still found in circulation in the US, and if you buy on at a coin store they may charge you .10 Euro for a brand new one.

 

Early cents were zinc plated? I only knew 1943 steel cents were zinc plated.

 

Duh. You're right, of course. For some reason I had it stuck in my head that 1982-present were zinc plated with copper and 1951-1982 were the reverse of that. It's an amalgam, of course, making oxidation that much easier.

 

No, you're still off-base. Pre-1982 cents (except for the 1943 steelies) have a uniform composition throughout -- and, since that composition doesn't include mercury (!), it's not an amalgam.

I'm not sure where you're going with this, but there's no "plating" on cents except for the zinc-coated steel ones and the post-1982 zincs.

 

In circles, chasing my own tail, I suspect. I meant alloy.

 

Alloy, gotcha. Zinc is certainly more reactive than copper or even tin, but I honestly don't know how brass, bronze and copper compare when it comes to oxidation susceptibility.

Anyhow, the green spots aren't just oxidation -- copper oxide is brown or black. With CO2, you get copper carbonate, which is green; with PVC residue, you get copper chlorides, which also tend to be green. "PVC residue" gets its own category from the TPGs, but the end result of it is corrosion.

 

Come On Bad Thad, get that book on Verdigris published !!!

Jim

 

Man, Jeff. I wish I'd stayed quiet and let you answer the post. My knowledge of metallurgy and chemistry doesn't go much further than being able to spell the words. You hit it right on the head, where I snuck up to it and tried to club it to death from behind. Thank you for setting me straight and clarifying things for the OP.

 

Most important thing is the question gets answered correctly. We all have misspoke, (typed), here before.

 

Bad Thad has done a lot of analysis of copper corrosion with the most advanced of lab equipment, and I have been encouraging him to publish it with the great photos he has. Maybe as an ebook even. Here is the original thread on this. Many do not have the chemical background to research , but his writing ( which I have seen) is comprehensible to those with just a little chemistry knowledge.

http://www.cointalk.com/t68347/

 

thank you all for the reply's
My biggest fear was that it would be PVC damage or something.

 

Heh. I'm trying to practice my "answering skills", but it's really just a placeholder until BadThad shows up...

 

has the book come out yet???

 

maybe stupid question, but is it "contagius"
I meen, if i have other coins that where once in contact with this coin (it are coins i recieved from pocket change from someone that went to the us) can the other coins develop the same problem?
Anyway, i will replace it when i have the chanse, but like said, it wont be the easyest to replace for me