Unfortunately I am able to see the date an mint mark on this penny and am saddened by the loss.
This creeping green fungus/bacteria or whatever, contaminates every single cent it touches.
I realized there is no sense in trying to save any of the pennies that have even a little spot of this green stuff on them.

Corky

i have a 1920 cent like that!!!

where did u store these coins if i may ask

One of our friends had been saving them for a long time and gave up on his kids or grandkids taking an interest in them. My husband told him that I collect pennies so our friend offered them to me. I imagine they were stored in the worse of conditions. They were all in three 2 pound coffee cans and one old canning jar.
Fortunately I was able to save quite a few. It is probably just as well that I don't know what I am actually missing.

The coins in the picture are actually ones I had tried to clean with my boiling water and baking soda treatment. I was able to save several hundred coins out of that batch. The problem is, now the coins are toned in vibrant colors and not quite what a serious collector would want in their collection. I will try to get a picture posted of the other 'after treatment' coins soon.

I have about 600 or so coins that I found interesting enough to put aside to check again. I know I found die cracks and some other anomalies to photograph. All I have to do now is get my interest back again...

It will be a few days because we have company from out of town and I won't be able to get on the computer for awhile. I guess company comes before pennies?

Corky

must have been stored near a damp place or something :/ too bad for all those lincolns :'( wish u luck to pass ur nightmare

Corky,

I did not see a picture. When copper is exposed to moisture, it oxides green rust. That is probably what you are seeing. It is likey they were stored in a high humidity are of relative warm temperatures. I do not see a picture with your post (maybe cause I am a new member) but you might try heating that coin to 160 on warm in the oven with the door open (will also kill lichen and mold too) and then brushing off the oxidation with a soft bristly brush (toothbrush?) and then storing in sealed slabs. Storing them in the fridge in that sealed container would also slow down any oxidation. Do this on a warm, low humidity day in summer. Or just store them in a sealable container with moisture absorbing packets of silica or even packets of flour.

You can recharge the silica packets by putting them in the oven on warm too and driving off the moisture.

-UncleKin

Thank you for the suggestions.
I will give it a try at some time.

Right now the coin is residing in a much better environment, but separated from its next of kin. No need of causing another plague.
It was in coins that a friend gave me that he had been storing in three 2# coffee cans and one old mason jar.
Of the 12,000+ coins many of them had been contaminated with the green grunge, plus a black growth that was quite unusual.
I managed to save a great number of the coins by boiling them on the stove and adding baking soda and boiling until the water was very dirty. Then I rinsed the coins in warm tap water and secondarily in distilled water.
After all is said and done I was able to save all but about four rolls of pennies.
This isn't a way I would recommend for the average 'I want to keep it penny' because it changes the appearance of the coins and can discolor them.

Corky