The interesting posts below makes me think this subject may deserve some additional input.
The debate over dipping and the associated loss of metal from the coin is an agrument that has been around for quite some time with US coins. On the side of 5c, Weimar W. White (a chemist) has written a wonderful little book that explains in detail why dipping should be avoided, and if done, results in the loss of coin metal. Proper storage is also discussed. This book is entitled: Coin Chemestry, Including preservation and cleaning.
Mr. White goes on to explain the scientific chemical changes on the surface of a coin caused by corrision (aka toning). Weight loss from dipping is discussed (in micrograms). White doesn't simply explain why it occurs, he also discusses ways to keep coins from this natural process - and how sulfur and coins don't mix. One of his topics is entitled: Toning is to silver what rust is to iron. It is not difficult to determine what side of the debate he sits on.
He also explains how the degree of toning can be determined by the color of the piece. Toning results in color changes in steps. From untoned, the progression is: yellow, red, blue, and finally black, I don't recall if green is before or after red.
If there is any doubt where Mr. White stands on the subject of dipping and toning, consider this statement:
"I have suggested in a number of coin publications that lightly toned coins be graded Uncirculated instead of Mint State if no physical wear is evidenced. Toned coins are not Mint State. They did not come off the coining press chemically toned or corroded. Objectively, coins cannot improve in grade due to chemical wear after being minted. The darker the sulfide toning on a silver coin, the greater the chemical wear. Just remember, the color after blue is black."
Now, I am not claiming Mr. White is correct in all his assumptions, though I credit his chemistry as certainly being hard to refute. By his statements, I would infer that he does not accept market grading - at least as a factor of toning, though eye appeal represents more than simply color. He is a strong proponent of the use of Intercept Shield developed by Lucent Technologies, to prevent toning from occurring, For those not familiar with this product, it can be found as part of an ICG slab, as well as part of various numismatic storage products. Boxes and individual sleeves can be purchased to help overcome the effects of sulfur and long term storage.
For those who wish to read more on the subject, here is a link to the book itself:
It is a little tougher to locate than I expected. Amazon, for instance is out of stock.
This is a subject that I do not recall being discussed on this site, but certainly one which does deserve consideration. I would definately recommend this book be added to the collector's numismatic library,
CCRS member since: 4/2/2003
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Coin Chemistry (jmc, 3/7/2011) Re: Coin Chemistry (Dave in the Grove, 3/7/2011) Re: Coin Chemistry (5cents, 3/7/2011) Re: Coin Chemistry (Dick, 3/7/2011) Re: Coin Chemistry (token hawk, 3/7/2011) [this post has been deleted by its author] (3/7/2011) [this post has been deleted by its author] (3/8/2011) Re: Coin Chemistry / grading observations (jmc, 3/9/2011) Re: Coin Chemistry / grading observations (AussieBob, 3/9/2011) Re: Coin Chemistry / grading observations (5cents, 3/9/2011)
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