Indian Head Cents - What Causes This?

I dunno...maybe these pennies were stored in rolls that became damp? If the paper rolls had any acids or sulfates it would certainly hasten corrosion in areas with direct contact. Just a guess...copper is a pretty reactive metal--a lot can happen.

Probably shouldn't bore you with the reason but just in case you are aware of some Chemical terminology, here is the reason(s):
All forms of copper products, regardless of the actual composition, will eventually combine with cetain gasous materials such as Oxygen. As Oxygen combines with the Copper in a product, your coin, it slowly darkens to form Cu2O, Copper Oxide. (The numbers are actually supposed to be lower indicating quantities of atoms/molecule. Where none shown, it is supposed to be 1) This process continues as long as Oxygen is present. As this occurs in nature the now Cu2O is attacked by Carbon Dioxide, CO2 and Moisture, H (OH). Note moisture, water, is in reality Hydrogen Hydroxide where the (OH) radical is actually the permanent compound. The ending results is the darkened Copper now attains additional greenish discolorations which is now the [CuCO3-Cu(OH)2] or Copper Carbonate. Now this substance is ready for even futher attacks from substances in the air. The worst is the results of burning Sulfur rich coals in power stations, steel mills and factories with boilers. The Sulfur end up in the air as SO or SO2. This now combines with the moisture H(OH) to form either H2SO3 or SO4 commonly known as Sulfurous or Sulfuric Acid and is occationally noted as Acid Rain. As this also attacks the Copper, the loose H ion is replaced with any loose Cu ions to help form CuSO4 which is a dark green crystaline structure. This is common even on Copper piping for the home, Copper Gounding systems, Copper antennae, etc. and is prevelent in some areas such as Norther Indiana where many Open Hearth Steel Mills once operated.
Sorry for the long explanation but you did ask.

carl - How come only the Indian Head cents turn into these "blackies" and "greenies" and it doesn't happen to the copper lincoln cents? I'd understand if it was a process that takes a century to occur, but it seems very common in even the latest years of indian heads, yet I've rarely seen an early issue or teen dated penny with similar coloring.

Well...I'll just add that during the recoinage in the 1870s, the mint remelted millions of coins to comply to the Mint Act of 1871. One result was a lot of poorly alloyed coinage stock that resulted in streaked cents well into the 1900s. With the poor alloying, I wouldn't be too surprised if corrosion was not refined from the remelt, resulting in planchets that were more susceptible to corrosion later? I'm not a metallurgist, but I have read that early coppers became black quickly because of planchet impurities.

Be sure to post back and let us know how that urine test works out.

Urine dips all around! hahah

I have a couple of those "blackies" too mahgobbi. I have a 1906 that I would honestly describe as MS65+ if not for the blackness on it. No corrosion or ugly little green spots on it at all. I've often wondered what happened to it to get this way....

--Gary

EDIT: 50 posts! wahoo!

Ahhh yes, the Urine possibility. For sure much cheaper and safer than chemicals purchased. If you live with someone I'd like to hear your explanation to them of what your doing. Now remember that this substance is constantly changing pending on what you eat and drink. So if you do use this, make sure you document what you drank and ate prior to so we can all do the same if successful. And be sure not to use items that may contaminate the Urine such as recovered from a urinal. Must be pure or all is lost.
Remember that any acid product will remove some of that contaminate but the strength may also damage the coin. Many try household acid type products first. Such normal household items as Coke, Lemon or Lime Juices and some swear by Tomato Juices. If you attempt to try any of these let us all know the results.
Note that if the contaminate is a Sulfuric Acid type it may well be soluable in distilled water. With a dip in that, nothing to loose.
And for those that constantly utilize the term of Verdigris, note that is a substance produced from exposure to an Acetate only with Copper. This is known as Cu(C2H3O2)2-H(OH) and has little to do with normal Copper coin contamination. An so ends Chem101.