The words tarnish and patina both refer to changes on the surface of a metal caused by chemical interactions like oxidation, often referred to as toning. While patina is often seen as desirable, tarnishing is not, but they are both referred to as toning on coins.
Is There a Difference Between Patina and Tarnish?
Tarnish and patina are very similar. Technically, patina is a kind of tarnish. Both tarnish and patina form a protective layer from interactions between the surface of the coin and its environment. Both change the surface color over time to protect underlying layers of metal. In common use, toning and patina may both be used to describe coloring and darkening on coins.
What is a Tarnish?
Tarnish is the thin layer of corrosion that develops over metals like copper, brass, and silver due to oxidation on the surface layer of the metal. While tarnish is generally synonymous with a loss of quality, like a “tarnished reputation,” tarnish on coins is often desirable and is also referred to as toning.
It forms to protect the metal beneath the surface layer and is self-sealing. Tarnish often appears as a dull black or gray coating of film over the surface of a coin, although colorful layers of tarnish are sometimes found on silver coins like the Morgan silver dollar. Tarnish can be attributed to either exposure to oxygen or sulfur dioxide, although it may not always rely on oxygen.
What is Patina?
A patina is a thin layer that forms on the surface of metals like copper, brass, bronze, and metal alloys due to oxidation. On coins, patina is typically known as toning. It can form red, blue, green, and other colors, although it is most commonly green. Differences in a coin’s composition can impact the patina that forms, and different patina will form on bronze coins than on copper coins, like the Lincoln Wheat cent.
The word patina is Italian and refers to a shallow deposit layer on a surface. It comes from the Latin word patina, meaning pan or shallow dish.
Why do Silver Coins Tarnish?
Silver, as it is found in nature, is alloyed with other metals like gold. Before it is coined, the impurities must be removed through refining methods, and after it has been refined, it can be minted into a coin. As soon as the coin is struck, environmental contaminants like sulfur dioxide begin to tarnish or tone the surface layer of the coin. Toning is a slow process that often takes place over years and decades, so it is more common to find it on vintage or historic silver coins than recent issues.
Are Toned Coins More Valuable?
Tarnishing or toning can add value to silver coins, depending on the eye appeal of the tarnish. Some silver coins with rainbow toning or unique colors may have a slightly higher premium than others of a similar grade and issue.
Can I Remove Tarnish or Patina?
There are effective ways to remove tarnish and patina, but it may not be advised. Toning may add value to your coin, especially if it is deemed to be attractive toning. Attempts to clean the protective layer on the surface of a coin, whether it is vintage or ancient, are often detrimental to its integrity.
Does Gold Tarnish?
Gold is one of the least reactive metals. It does not react to environmental contaminants in the air like silver and copper do. However, a gold coin that is alloyed with other metals like copper or silver may develop signs of tarnish or toning.
