Why Are Some Cents Black or Red?

I have a numerous Lincoln cents that have either a black or red coloring. Is this a patina? If it is, why is it on a few of the cents and not all. I also have Canadian and foreign copper coins that have the same effect.

The pic shows a normal, newer cent, a circulated cent with typical coloring and then below them, a black cent and a red cent:

 

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what years have you found the black and red cents in? do you find the black cents mainly in the mid-40's?

 

I have them from all decades right up to 2002.

 

just from the conditions that they have been circulated in.

 

Copper(1) oxide Cu2O has a reddish color
Copper(2) oxide CuO has a blackish color

The one listed as "normal" has a specific proportion of the 2 oxides along with various sulfide and environmental elements
The one on bottom left has a higher proportion of CuO, whereas the one on the right has a higher proportion of Cu2O, both along with environmental compound reactions ( often read of such red coins as being exposed to iron if it has been in soil ). IMO.
High levels of CuO is small spots are often called "carbon spots" due to their color, but not produced by carbon reactions.


Jim

 

This is an old picture - I'll have to get some new ones, this subject keeps coming up. I took this pic as joke, something along the lines that I collect toned coins too I like red ones. I do have sets labeled RED, BLACK, PURPLE and GREEN! These are all naturally toned, pulled from huge bulk batches for their color. The wet shininess was a coat of olive oil trying to get the color to show up better in the photo.

 

Red in all years, black mostly in the 40's - I never saved or have looked for any memorials.

 

Thanks for the explanation, Jim! It's been bugging me for so long and I never even considered it to be two different oxides, which makes a lot of sense. CuO=red'; Cu2O=black.

Now, I can rest easy!

 

I am certain it is not just the combination of the 2 only. Storage differences can limit the amount of oxygen and environmental sulfides can certainly play a part. This is my theory, maybe someone with better analytic equipment can verify it. Thad will maybe jump in

Jim

 

I guess I should mention for any real copper newbie, "RED" as in coin grading lingo is the "normal" in the OP. The others are "BROWN", although I am not sure what they would grade the red one, but certainly not "RED", maybe corroded or environmental damage. Anyone ever see one that color graded by PCGS

Jim

 

Yes, I understand what you're saying. I have a few that I've dug up while metal detecting that I keep as reference to compare to coins I find in rolls. Different environments have different effects and I've got them identified as to where they were found and what the conditions were.

 

Here's a link to a page which seems to have been very carefully assembled.
It shows color designations and the coins shown are usually excellent examples of their stated color(s).
Still, you may disagree with some of the designations. : )

http://www.coinpage.com/lincoln cent-pictures.html