PCGS The Standart for the Rare Coin Industry

Whether a piece should be dipped or not is a matter of opinion, and there are arguments on both sides of the fence.

Less in question is the procedure of removing dirt, oil, grease, and other contaminants from a coin's surface by using plain soap and water, acetone (obtainable at drugstores; acetone is inflammable and must be used with great caution under well ventilated circumstances), ammonia (which may discolor copper coins but not silver and gold issues), or other solvents. In general, my advice is not to use a solvent or any other substance on a valuable coin unless you have experimented with inexpensive pieces first.

In the negative category are various processes which can be described as "cleaning." This term is normally not used to describe pieces which have been dipped or which have had dirt removed by the use of solvents. Rather, "cleaning" refers to the use of jewelers' pastes, polishes, pastes made of baking soda and water, and other methods which use friction or a combination of friction and chemicals to remove metal from a coin's surface. Shortly after the turn of the century Farran Zerbe visited the National Coin Collection on view at the Philadelphia Mint and reported to readers of The Numismatist that the silver coins had been cleaned multiple times with jewelers' paste, thus considerably lessening their value.

Excellent commentaries on the subject of cleaning can be found, as noted, in Photograde, and also, relative to copper coins, in Dr. William H. Sheldon's Penny Whimsy book. In the latter reference, Sheldon tells how to judiciously retone copper coins which have been cleaned.

Attractive toning can often add to a coin's desirability. In the silver series, halo-like toning of iridescent hues is particularly desirable and is usually caused by the storage of coins in cardboard album pages of the old-style, such as those marketed under the National, Raymond, Meghrig names. These pages contained sulfur as an impurity in the cardboard, and over a period of time the sulfur tended to act on the coin, from the rims toward the center. The rims would tone first, and gradually toning would go toward the middle.