Coin toning is not a factor that is usually considered when a coin is graded, but needless to say, knowledge pertaining to the natural coloration of coins or coin toning can be useful when determining the value of a coin. A coin that exhibits an attractive natural toning, depending on the metal used to mint the coin, normally attracts higher prices.
The value of a coin can be immensely influenced by the attractiveness of its coloration or toning. Unnatural coloration or toning for example provides a clear sign that a coin was treated or cleaned, impacting heavily on its value, while natural coloration or toning might add value. In order to determine the original color of a coin, it is necessary to know how the color of the metal used to mint the coin changes over time (or vice versa). Our focus here will only be on the four main metals which are normally used in coinage, namely silver, gold, copper and nickel.
A freshly minted silver coin usually has a bright silvery-white surface with a great deal of luster or brilliance. However, a silver coin tends to color or tone to a deep brown or black over time as a result of its chemical activeness. The multi-colored iridescent hues that Uncirculated and Proof silver coins normally exhibit after a few years can be highly attractive, which can definitely increase the value of the coins. Beginners tend to go for silver coins which display luster or brilliance, while advanced collectors prefer silver coins that exhibit attractive and natural coin toning. On the other hand, circulated silver coins tend to have a dull gray appearance and in some instances even deep gray or black areas. This is normally where the beginner steps in and starts to clean a silver coin in order to obtain a luster or brilliance, destroying the collector’s value of the silver coin.
Freshly minted gold coins tend to be a bright yellow-orange color with a great deal of luster or brilliance. Now given the fact that gold coins are not pure gold, but normally alloyed with other metals such as copper in order to make it harder and more durable, it tend to color or tone over a period of time. In fact, gold coins normally exhibit a deep orange after several years and in some instances light brown or orange-brow toning “stains” or streaks in certain areas. This doesn’t really affect the value of a gold coin, provided that the toning is light.
Now when gold coins really get old, especially circulated gold coins, red oxidation might appear. In addition, gold coins that are recovered from ship wrecks normally show signs of corrosive action caused by sea water. Needless to say, this negatively impacts on the value of such gold coins, although it must not be confused with cast copies.
A minted copper coin usually features a brilliant pale orange surface after emerging from the dies. However, due to copper’s chemical activeness, it instantly starts to oxidize (combines with oxygen) when exposed to the atmosphere. This will lead to a glossy brown surface over the years, especially when exposed to sulfites and actively circulating air, with part red and part brown stages in between.
When a freshly minted copper coin stays out of circulation and retains its original mint luster or brilliance, undergoing subtle coloration, it is normally described as being “Brilliant Uncirculated” or in a “BU” condition. If the copper coin remains uncirculated and gets to the red and brown stages, its condition will normally be described as “Red and Brown Uncirculated”. If the copper coin remains uncirculated and its surface is predominantly brown, it will be called “Brown Uncirculated”. In terms of value, an uncirculated copper coin that is in a BU condition with full original mint luster or brilliance will fetch a higher price than a copper coin of the same type and year, but which is in a “Red and Brown Uncirculated” or “Brown Uncirculated” condition or state. Thus, the less oxidation a copper coin has been exposed to, the higher its value should be in relation to a copper coin of the same type and date. Needless to say, circulated copper coins are not as valuable as uncirculated copper coins (assuming coins of the same type and date). The reason being is because circulated copper coins tend to be toned in numerous shades of brown.
Freshly minted uncirculated nickel coins are silver/gray in appearance, and although not as bright as silver coins, have some luster or brilliance to it. Nickel coins however tend to turn to a hazy gray after some time, especially circulated nickel coins.
Now needless to say, the above-mentioned info provides a nice basis for distinguishing between coins exhibiting a natural tone and those that exhibit an artificial or unnatural tone. Good news is that experience has shown that coins that fall in the last category can be identified with relative ease. However, without getting into much of the detail here, professional coin doctors, those who deliberately change the condition of coins for deceptive or misleading purposes, can in some instances make it extremely hard to distinguish between coins exhibiting a natural tone and those that exhibit an artificial or unnatural tone.