NCS Conservation: Environmental Damage

Posted on 11/8/2016

Environmental damage occurs when the surface metal of a coin oxidizes due to the interaction of chemicals and moisture in the immediate environment.

Most damaging impairments to the surface of a coin are often divided into two large groups. The most common are known as “environmental damage.” By definition, environmental damage is any serious and often permanent change to the surface metal of a coin. This type of damage occurs when surface metal oxidizes due to the interaction of chemicals and moisture in the immediate environment.

Environmental damage ranges from mild to severe. Staining is considered a less severe form of environmental damage. Typically afflicting silver coins, the surface metal has oxidized in a uniform manner to create a milky opaque appearance. The most severe stage of environmental damage is corrosion. Corrosion often appears as spots and, in more advanced cases, over the entire surface, that are often raised. The coin has a different texture than a regular undamaged surface. Corrosion is usually colored, such as black on a silver coin or red, orange and green on a copper or nickel coin. The simple term "environmental damage" will usually refer to oxidation damage on a portion of a coin surface.

1876G Germany 5 Pfennig
This nickel coin had some minor environmental damage that professional conservation
was able to address with little permanent effects.
Click images to enlarge.

Click images to enlarge.

Among the most common ways a coin may become environmentally damaged is when it has been buried in the ground for some time. Chemicals in the soil bond with metal atoms in the presence of water that acts as a catalyst to create the corrosion on the surface of a coin. Other environmental factors could also cause irreversible permanent surface metal changes such as extreme heat from a fire. Even long-term storage in a bank vault can create the right conditions for the development of minor forms of environmental damage when storage materials, such as paper or cloth, have time to combine with humidity in the air.

(1355-75) France 1/2 G
This medieval French coin was likely in the ground for some time and developed
some tell tale green environmental damage.
Click images to enlarge.

Conservation was able to remove most the green without revealing much permanent surface damage.
Click images to enlarge.

China Yr 10 S $1
This silver coin had likely been buried in the ground for some time and
developed a red/green residue and environmental damage.
Click images to enlarge.

While not always the case with coins that have developed damage such as this,
conservation was able to remove the marks without revealing much permanent damage.
The ink stamp on the obverse was also able to be removed.
Click images to enlarge.

Environmental damage can also occur under certain storage conditions. As is frequently discussed, the chemical PVC that is in some cheap coin holders—most frequently soft flips— can leach out and deposit on the surface of a coin. This is a prime condition for the development of corroding environmental damage with the presence of humidity in the ambient air. Holders that are less-than-airtight could allow environmental conditions to begin the process of oxidation and environmental damage.

In most cases, professional conservation can minimize the appearance of environmental damage and prevent any further damage. Surprisingly, coins with the least severe forms of environmental damage often have the least change following professional conservation.

Prevention is the best remedy to prevent a coin from the ill effects of environmental damage. Your choice of coin holder holds the key. The holders used in NGC certification provide the best protection against the threat of environmental damage.

For a list of NCS Conservation tiers and services, click here.

NCS is an independent member of the Certified Collectibles Group.

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