I purchased a few coins no too long ago that were in
good shape, but in the dealer photos,
had an orange shade to them. I thought that was odd, but the detail and
price was such that I couldn't pass them up. When I actually received the coins, they were much darker than the photos, and looked a dark brown rather than the orange shade inf the pictures.At first, I thought it was just the lighting in the photographs, but examining them further, I could tell that the coins
had been chemically repatinated.
Still, with the detail on the coins and the very, very
low price, I couldn't complain. Then, a few days ago, each one of these six coins broke out in spots of
bronze disease. After treatment of the coins, they came out looking orange - just like the dealer photos. I'm thinking that these coins were treated before for
bronze disease, causing the orange tint in the pictures, and then
toned afterward. When I re-treated the coins, they turned back to their orange tint. My guess is that the sodium in the BD killing solution is speeding up the process of oxidation of any ferrous substance present in the
alloy of the coin, causing the orange (and sometimes
red, if there is enough iron present) color.
This in effect would be corrosion of the base metal of the coin, and I suppose that over treatment of a coin rich in iron could lead to
pitting. But, considering the alternative... I would rather deal with that than the corrosive effects of HCl in
bronze disease.
