I am a newbie to the forum but I have an oddity. I found a brass (yellow) cent in a roll of coins from my local bank. I know that brass cents were made in the eightys but other than the gentlemen who found a brass cent in 1979, I have not found a history of brass coins produced in the 70's. Can anyone enlighten me?
Toning can possible cause that kind of coloring, and unless you can prove that it's really UNC, it can be quite difficult to do so. Maybe you might want to weigh it to see if there is some major mass difference. As well as, do post pictures if possible.
From a technical perspective, all pre-'82 cents are brass. The definition of brass is an alloy composed of copper and zinc. Pre-'82 cents are composed of 95% copper and 5% zinc with a tiny percentage of tin thrown in. That makes them all brass. Granted, there are various forms of brass with higher copper/zinc ratios, you can find the standard conformance table - HERE. Regarding the differences in coloring of US cents, it can be attributed to several things. It can be toning as mentioned, it can be a bad alloy mix or it can be a result of planchet washing. But it is not uncommon to find the coins in various colors even fresh from the mint.
The last of the tin was removed in 1963 so all cents from 1963 - 1982, plus some of the 82's are brass. The 1947 - 1062 cents are bronze. Bronze is defined as an alloy of copper and tin, sometimes with other metals as well. So once you have the copper and tin it is bronze with zinc.
It varied, the specific language of the law simply specified that it should be 5% tin and zinc. The actual amounts of each metal used was left up to the mint and at different times during the life of the bronze lincolns it has ranged from as much as 4% tin to as low as .1% tin. During the early years was when the tin content was highest but for most of the 1909 - 1942 period it was about 2.5%. The tin percentage went through a slow and gradual slide from 1947 until the legislation was changed in 1962 to allow for its elimination.
