1974 S Penny Mint Mark

Thanks CentStation. This is the first time I have heard of copper cancer. I found out it is irreversible. So if I see any signs of copper cancer on a rare coin, is that coin only worth face value?

I thought I was seeing splits in the S on top and bottom like this from coppercoins.com. I may need to get new glasses.

A few things:

- I think you do have the only reported repunched MM for the 1974S LMC [congrats] but, better pictures would prove that. I see what looks to be a secondary, the MM position is extremely close and yours looks to be a small date '74 [though that is difficult to prove]. If you see split serifs, then you are probably good.

Unfortunately, the coin is dinged up and the 'copper cancer' I referred to is what is commonly/erroneously called a carbon spot and it will eventually cover the whole surface and is [basically] the beginning of the end.

Originally you asked about a D/S or S/D, which is an OMM [over MM] - I don't see evidence of that.

Your coin is definitely a 1974 small date cent. The spot you see on the date is a carbon spot. Your 1974 S Lincoln is a copper coin unlike cents minted after 1982. 1982 was the transitional year when the U.S. mint switched to a zinc core/copper plated cent while at the same time some cents were still being produced in the normal copper composition. I'm not sure how "zinc rot" got thrown into the mix here being that your coin is copper but that does not apply. A carbon spot is what it is but in my opinion is nowhere near as 'fatal' to a Lincoln Cent as zinc rot can be. I have seen carbon spots on copper cents, which can enlarge over time, and I have seen zinc rot consume a zinc core cent pretty bad. With all due respect, I have never seen a carbon spot cover an entire copper cent. You may or may not have an RPM here. Hard to tell from your pics but there is a possibility from what I can make out. If so, it is not the first reported or they would not have an example already listed. "Copper cancer" is a blanket term used for both carbon spots and zinc rot. Carbon spots will be found on copper cents and zinc rot will be found on zinc core cents.

http://www.varietyvista.com/Mystery...%20Punch.htm

A little extra reading material for those interested in the nuances of the LC mintmarks.

With incredible photography from Ray Parkhurst. http://macrocoins.com/

The spot we see is just the begin of what later will be Verdis, Zinc has nothing to do with. the zinc on this alloy was use just to give more resistance to corrosion but is not word end protection. I like the term "copper cancer", the verdi is a copper oxide which has the form almost identical with cancer cells or tumors.

Is just damage because cleaning those points or the oxide let holes and traces.

merclover I like your patience to explain in numismatic term.

For long time I want to compile this extract from the McGill medical school course of Chemistry of the organic and amorf oxidation

Carbon is not involved in these surface finish anomalies and the process is not oxidation (so often described as the chemical
process). The culprit is sulfur and the process is sulphatization.

Carbon spots are found inside diamonds [inclusions from imperfect pressure during formation millions of years ago] ? not on the surface of coins and medals. The proper term in
numismatics should be ? SULFUR SPOTS.

These dark brown to black spots appear on both copper (including bronze) and silver coins (including silver clad).
These are formed, not with contact with carbon, but contact with sulfur from the environment. The sulfur comes from any variety of sources. The curing of rubber, for example, includes
sulfur by vulcanization. Thus rubber should never come in continuous contact with coins and medals.

Sulfur is also used in some manufacturing processes of paper. This is why coins tone in certain paper envelopes. Anti-tarnish tissue is made without any sulfur at all.

Sulphatization is a greater problem for the field of frescos than coins and medals. Here a sulfur atom replaces a carbon atom, physically changing the plaster UNDER the pigments of the
paint. In numismatics at least our sulfur problem is on the surface of the metal, where it can be treated.

More evidence is color. When carbon reacts with copper ? as copper carbonate ? the resulting substance is blue-green! Not brown-black.

Here is an experiment you can do yourself to prove the villain is sulfur, not carbon. Take any uncirculated coin, bronze or silver. The commonest source of sulfur for most people in
daily life are elastic rubber bands where sulfur was used in its manufacture. Place the coin on top of the rubber band so it stays in physical contact undisturbed for weeks at a time.
After months you will see a black line where the continuous contact was made, the sulfur reacted with the copper or silver to form copper sulfate, or silver sulfate.

Do something similar with carbon. Place in contact with an uncirculated coin any form of carbon ? diamond, coal, pencil lead ? and leave for the same time. Nothing will happen!
Try to speed up the chemical reaction by introducing oxygen, water, heat, pressure or whatever. It will still yield the same result, nothing.

In the finishing of high relief medals, as applying a ?French finish,? sulfur is the good guy. An active chemical containing sulfur is used to purposefully apply a darkening to the surface
of bronze or silver medals. With the use of ammonium sulfide this takes place in seconds! Medals totally immersed in this chemical must be withdrawn within ten seconds and immediately
washed with water to stop the chemical action!

Thanks for the patience to read. I do not know who wrote this or any kind of copyrights. It is a part of our studies materials in that time.