Issue with a 1964 Presidential Coin Set

I still think it came from the end of a roll and tarnished in the roll. But again that's just my guess.

 

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Maybe the difference in toning is due to the mixture of silver and alloys. We all know that copper "woodies" are created because of a bad or incomplete mixture of copper and alloys. Possibly the same is to blame for how the quarter reacts to the environmental elements.

 

As Idhair said, we can only speculate as to the old tarnish stain. I don't think it could be an alloy problem because the ingots are rolled out, so i would expect any inhomogeneities to be elongated, not circular in the center of the planchet.

I don't know how you tell if the tarnish was on the planchet prior to minting. If the tarnish was sufficiently thick, it might leave a mark at the interface or there may be differences in metal flow between the black and silver regions, but you might need some SEM analysis to prove it.

Like William of Occum, I think the best guess is the simplest. End roll toning seems to make the most sense. It seems reasonable to think that MW used rolls to assemble the sets, and who knows what kind of environment they were exposed to prior to opening. No way to be certain, but I think this is a reasonable explanation

 

I hope to have a better picture taken by a friend that might give more detail concerning your response. As for the assumption that MW used rolls to assemble the sets; it makes much sense. As a silver stacker for years, I still can not comprehend the amount of tarnish on the coin after 1 year, even at the end of a roll. Plus, in the display case for 50 plus years, it has not got any worse than the 1st day I saw it. All responses have been possible, and I have been taking the information to heart.

 

No idea if this is correct, but here is a possible explanation on why the coin has the black level of dark toning for over 50 years. Toning is caused by the silver atoms on the surface of the coin reacting to other elements such as oxygen and particularly sulfur (simplified explanation). The speed of the reaction will depend on the environment and concentration of the contaminant. As the sulfide layer gets thicker the color will turn darker. Over time, there is less “fresh” silver left to react and it takes longer for the sulfur to penetrate through the toning layer. At some point, the toning will slow as the coin darkens.


If the coin was exposed to a highly concentrated sulfur environment as it sat at the end of a coin roll, the exposed surfaces could tone very rapidly. Once removed from this environment and placed in the display, toning would slow. The newly exposed fresh surfaces would tone over time, but the dark area, with the thick sulfide layer would not appear to get much darker.


Once again, it’s unlikely that the actual cause can be determined but it’s interesting to speculate and I think this explanation may be a good possibility.

 

Thank you Oldhoopster for the information. It is very likely you explained the amount of tarnish and why it did not worsen. I think you slammed dunked the response!