Unusual toned spot on gold bullion coin

[wavysteps]

I ran across this unusual toning on an "American Buffalo Bullion" piece today and was wondering if any of you had ever encountered the same condition. The year of the coin is 2006 and it was discovered by the person who had order it from the mint.

The frosting in that area has no die defects and remains continuous with no scratches, gouges or any type of mar, except for the discoloration.

Any ideas as to the cause? Or, have any of you seen this condition before?



Thanks for any help that you can give.

BJ Neff

PS - the colors of the discolored area are a faifly true match to what was seen

[Steven]

Possibly another metal. Copper/Silver maybe. Could be that a minute amount of copper alloy near or on the surface of the coin has caused the discoloration.

Has the look of a small line down the middle though as if something had been lying on it then fell off. ??????????

I've seen this look on copper coins when a speck of something attaches and a toning begins to spread from that point.

Unfortunately about the only thing I know about gold coins is that I can't afford them


Maybe someone that knows will jump in here. See if I'm close about the copper alloy thing
Steven

[diamond]

There was a problem with reddish discoloration due to oil on the planchets. I don't know if this spot of discoloration owes its existance to the same cause.

[Steven]

BJ,
Another possibility in the line of oil, as Mike stated, maybe a thread from a cloth contaminated with oil got onto the coin long enough to cause the discoloration and the pattern that it left.

Just a thought.
Steven

[wavysteps]

Hi All - Got to thank you all for your replies. It was a question that came up at the CFCC coin show and I direct the dealer to look at this forum for possible answers and of course you all did provide some good ones.

BJ Neff