1991 Guyana 10 Cents-Odd Color

Greetings all.
I have just received a 1991 Guyana 10 Cents coin, but it has some very odd coloring.
Please see attached pictures.
From what I have found online, it should be more silver, this one is not.
The picture has a nickel next to it so you can see the color difference, I could not adjust the light anymore.

If it was a Lincoln cent, I would call it red/brown.
The weight is exactly 2.7 grams, which tells me it's not missing a layer, nor has it been coated with anything.
Here is the Numista listing link: https://en.numista.com/catalogue/pieces3472.html

If this is just a toned coin, it is VERY EVEN over the entire coin.
Any ideas or suggestions of what could be up with it would be greatly appreciated!
Darren

Hello Darren,

Let me start by saying this is pure conjecture on my part. I am always skeptical of coins made with the "wrong blank" so I try to find a PMD explanation first. If we assume the coin surface is copper then I would assume it was plated with copper after being minted. It only takes a very thin layer of copper to completely cover the coin. For instance, the current US one cent coin is copper plated zinc. The thickness of the copper is about 0.02mm (0.00079 in). A thickness of 1/2 this would provide complete coverage. So...using 0.01mm thickness and 18mm diameter coin and the density of copper (8.96g/cc), the total weight of the copper would be 0.044g, probably within the weight tolerance of the coin. If so, it should be easily verified by a slight sanding of the edge. Of course, I could be totally wrong, in which case you might damage a very valuable error coin.

Hello, rsirian1
LOL, I appreciate the response, however, I think I will refrain from the sanding option!
At least for now!
Thanks again!
Darren

1991 GUYANA 10 CENTS COIN: **COMPELLING MONSTER TONING ON BOTH SIDES** !So Cool!

There's your answer. It's just monster toning.

yes , nickle can turn every color silver can, including caramel with rainbows,
given the right environment for long enough.

Interesting that these coins seem to be prone to toning.

Anybody know the exact composition? I’m guessing it not the typical 70/30.

Definitely a very well toned coin.

Aidan.

I also found this on ebay: 1985 GUYANA 10 CENTS NGC MS 67 UNC BU TONED FINEST KNOWN WORLDWIDE for $400. This coin, certified by NGC also has toning as shown in the pictures:



Trouble is, the pictures of the same coin on NGC show no toning:

I have not had good results photographing coins with colorful toning.
The camera does not easily catch what the eye catches.

VERY INTERESTING!
Thank You ALL!
I have learned something new. I never really knew or thought that this kind of toning could happen.
It just seems SO even, on both reverse and obverse!
This coin may not be worth much, but it will definitely go into my cool and unusual collection.
Thanks again!
Darren

Cita: "Mr. Midnight"​I have not had good results photographing coins with colorful toning.
​The camera does not easily catch what the eye catches.

​Of course I agree with you but I would have assumed NGC would get the coloring right. Maybe not.

The toning also occurs on the 1990 and 1992 10 cent coins. I have those plus the 1991 toned coin.

This is why we put rolls of uncirculated coins by for generations to come.