What causes toning ?

Found this on a roll I got yesterday and I don't know much about toning on coins. Is this normal toning? Or was it left in a cup holder and soaked in coke or maybe some type of chemical. Whatever caused the toning seems to make the details on the devices sharper. I've seen a lot of rainbow toned coins here at CT but never quite figured out how it happens. Also, I think there's a die crack from the north rim and down between G and O on the obverse. I really want to get rid of the patina on the reverse to see if there's any details on the Lincoln statue but I know I'll probably mess up the coin if I try.

 

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Environmental Damage.. Toning could be from heat (fire, flame, smoke), chemicals (soda, coffee, cleaning agents), human bodily secretions (sweat, urine, oily skin)...
Your Cent does not look like natural toning but probably from one of the factors I mentioned IMHO

 

Flatulence

 

Laundry detergent. Somebody didn't empty their pockets.

 

Zinc cents tone before they leave the mint.

 

......almost anything and everything

 

I guess that means toning is the only environmental damage / human caused damage that actually ups the value of the coin? It's the type of PMD that TPGs actually "grade" which seems weird unless they have a way to figure out whether it's oxidation or not.

@Hommer I love mexican food and chili...I might be able to actually "design" coins.

 

What causes toning? Impure thoughts, just impure thoughts. This explains why we see more of it in recent years.

And don't ask what causes "milk spots". You'll go become a monk.

 

The two main culprits are sulfur and chloride compounds from the air and even from your hands (i.e., sweat, moisture). Milk spots are sulfur based compounds that we see with silver and gold issues. Confirmed many times in the lab. I really do not believe they are solely production based or from rinsing operations as I have read. Could be? but when analyzed in the lab high sulfur readings appear in these spot areas. Could then be the final end product (i.e., sulfur compounds) if you want to argue production process based initially. Whatever ... but for the modern issue collectors its indeed important.

John Lorenzo
Numismatist
United States

 

Thanks to all the folks who responded, I'm learning more and will read more about the different causes mentioned.

John : I'm not qualified enough to argue your production process but will definitely read more about it.

Thanks again all !

 

Try Coin Chemistry by Weimer. Simple ... but it proves my point.