All coins, medals, tokens, and currency are made from materials that will react with the environment. Metals will oxidize and tone, some with patterns that intrigue collectors. Paper-based materials can be made from cotton rag or linen that may not break down the same way as paper but can be damaged affecting its value. The key to storing your collection is to use product made from archival safe materials. Archival safe materials are those made without acidic materials or materials that do not turn acidic over time.

Acid free means that the pH (potential Hydrogen) measure is 7.0 or greater. A pH measure of 7.0 is neutral and greater than 7.0 is basic or alkaline. Although acidic materials will damage your collection, materials too alkaline will also cause damage. Those that produce acid free supplies with materials that is as close to being pH neutral as possible.

However, it is possible to be acid free without being archival safe. All paper contains Lignin, a bonding elements that naturally occurs in the pulp used to make paper that holds the wood fibers together. While lignin is not acidic, it gives offs acids as it deteriorates. If the lignin is not treated during manufacture, you can still have acid free paper but will become acidic as it deteriorates over time. The treatment involves dipping the paper in a solution that neutralizes the natural lignin.

Another storage item to stay away from is made from polyvinyl chloride (PVC). PVC is a very inexpensive plastic that is used as an additive to other plastics to make softer, more flexible products such as 2×2 flips used to store coins. PVC in itself is neutral but gives off a gas in reaction to the atmosphere that is acidic. The PVC gas will not only react with the coins but will deteriorate the plastic. The result will be a green or gray streaks or blob appearing on the coins. Because the PVC gas is acidic it will damage the surface of the coin. Once a coin is damage by PVC it cannot be reversed. There are ways to conserve coins that are damaged by PVC as long as the PVC contamination is on the surface. Once it mars the surface, the coin is damaged and its value diminished.

When purchasing plastic or clear storage items, hard plastics or those made of Mylar are the best choice. Capsule manufacturers use a neutral plastic that does not contain PVC while those that make 2×2 flips use Mylar. The makers of 2×2 cardboard holders also use Mylar and the cover sliders found in albums.

You can use the most archival safe materials but they will not protect your collection from environmental factors. The general rule of thumb is to stay away from the extremes. Do not store your collecting in a place that is too hot or too cold. Try not to store your collection in a place that is too humid or too dry since both could cause your storage materials to react. In other words, the average home with a temperature of 64-78 degrees with an average humidity of 30-percent should not be a problem.

Those living in colder areas where the home header is being used longer than other areas of the country may have to compensate. Forced air heating systems tend to dry the air that could cause damage to your collection. If you use a humidifier, whether built in to your heating system or a standalone unit, you might consider investing in a hygrometer to keep the relative humidity between 30 and 40-percent.

Where you store your collection also has to be a concern. If you keep your coins in a cabinet, the gasses from the wood and even the paint or stain used to cover the wood can cause damage. While wooden cabinets are attractive and practical, you do not want to store your collection some place that could add to the environmental concerns.

Metal cabinets are a better option. Safes and safety deposit boxes in temperature controlled vaults also makes great storage options aside from being able to keep your collection secure.

One of the factors that could cause wood rot in cabinets is excess humidity. If your home or where you store your collection cannot be controlled, you should use a desiccant in the area. A desiccant is a substance able to absorb moisture in the air. Two common desiccants are silica gel, the little packets that you see in some packages, and montmorillonite clay.

Choosing which desiccant to use depends on your situation. If your storage area is not that humid, use silica gel. It well suited for lower moisture area over a longer period of time, about six months. For high humidity areas, use a clay desiccant. Although it will not last as long as silica gel (about three months), clay is more effective at removing moisture when the humidity is higher. Another option is to use a combination, especially during seasons of high humidity. You can purchase silica gel and clay desiccants at many hobby stores and stores that sell collecting supplies.

While there are other types of desiccants, they are not recommended for use around collectibles. Calcium sulfate and calcium chloride uses sulfur and chlorine, both will not react well with the metals of your coins. Activated charcoal can add carbon dust to the air, which can attach itself to your coins. Some have suggested using salt as a desiccant. Salt is made of sodium chloride that would also introduce metal damaging chlorine into the environment.