Verdigris?

westflorida

Could someone tell me if it is common for it to form on silver coins. I have purchased a coin that I think is beautiful, although I am not sure if the green on it is verdigris or just toning. Is verdigris really harmful to the coin?

Thanks,

Louis

Might be PVC, which is damaging.

Conder101

If the green is on silver it is probably PVC contamination. Verdigris is a form of copper corrosion. It isn't a generic term.

BAJJERFAN

Verdigris is the greenish stuff found on copper coins. It is composed of basic copper carbonate.

Shamika

Don't forget, copper is alloyed into many different types of coins. Nickels get Verdigris all they time.

LanLord

<< <i>Don't forget, copper is alloyed into many different types of coins. Nickels get Verdigris all they time. >>

Nickels are 75% copper, pre 1964 silver coins were only 10% copper. I would think it would be more difficult to find on the silver coins than on the nickel coins.

carl

First of all Vertigris, as already stated is a carbonate. Vertigris is normally formed from contact with Acetic Acids. However, there is a form of carbonate that forms on copper coins but not as readily on silver coins. Remembering that modern day silver coins for circulation are not really silver but do contain copper such as already discribed. Per "New World of Chemistry" copper exposed to moist air first becomes coated with a thin layer of red cuprous oxide, Cu20. (Excuse my computer not having a lower case 2). Continued exposure to moist air containing normal Carbon Dioxide, CO2, react with the Cu2O to form a green layer of basic Copper Carbonate, CuCO3.Cu(OH)2 called Patina. Further, since Copper dose not readily react with Sulfuric or Sulfurous Acids, CuSO3 or CuSO4, but does easily react with CuCO3.Cu(OH)2 to form a Sulfate or Sulfite on the coin. This happens in areas where there is a sufficient quantity of SO or SO2 contaminates in the air.
Considering the original question is about the greenish colorations on a coin I would think it is not normal toning but a form of the above stated contaminate. Removing it would mean a loss of material as noted above. True Silver Oxides are normally very dark blue to black, not green. Stopping any further damage would mean cutting off the coin from the air. A normal 2x2, tightly stapled is not air tight but would help stop the contamination.

carl

In addition, if your new to coin collecting, you should know that cleaning coins is a no, no. However, if the coin is not a super expensive coin, you may want to try dipping it in Acetone. Pure Acetone is expensive, volatile, but will also not leave a residue.
I read in one of my many chem books that in some areas people use a weak solution of Acetic Acid to remove greenish contamination on copper. I tried it once on copper coins and it actually did remove any green formations but also cleaned the coin extensively. Tarn X would have done the same.
Oddly enough just recently, looking through old issues of The American Rigleman magazine I noticed an article stating that a method of cleaning brass used for ammunition that has a green discoloration was to use Viniagar containing Acetic Acid.