PCGS The Standart for the Rare Coin Industry

Coins should be kept in dry circumstances, away from industrial or other harmful fumes, particularly those containing sulfur. Homes heated by coal-fired or oil-fired furnaces often have sulfur in the air which does not seem to affect copper coins much, but which will turn silver coins light yellow or yellow-brown. Gold coins in nearly all instances will not tone but will remain brilliant, due to the inert nature of gold metal.

Dampness is harmful to coins. Copper pieces exposed to dampness will often exhibit oxidation and corrosion. Silver coins are also adversely affected by dampness. If it is impossible to keep coins in a dry location, then keep them in a tightly-sealed box in which packets of silica gel (available at a photographic supply store) are kept, to absorb the moisture. These packets can be refreshed at regular intervals.

If coins are stored in inert hard plastic holders this will be of great help, as these are usually airtight. On balance, technical grading considerations aside, it is my view that slabs seem to be performing a wonderful service for collectors of future generations, in that coins in slabs cannot be cleaned, "improved," or otherwise mishandled by their owners.

For many years flexible vinyl envelopes known as "flips" were used to store coins. They were easy to handle, and the coins could be seen clearly. It later developed that polyvinyl chloride (PVC) used to make these flexible envelopes leached out over a period of time and adhered to the surfaces of coins, causing bright copper coins to tone a dull hue, nickel coins to corrode, and silver coins to acquire a greenish slime. Although color cannot be restored to damaged copper coins, the effects of PVC can be largely neutralized by rinsing the pieces with acetone, ammonia, or a commercial product known as Dissolve. In all instances, adequate ventilation must be used, and the instructions on the container must be followed carefully.