As coins age, they develop a natural patina known as tone. Collectors and dealers
sometimes attempt to remove this toning and restore a coin’s shine. While novice
collectors may prefer this “cleaner” look, serious collectors know that removing
a coin’s natural coloring significantly decreases a coin’s value. Since the 1800’s,
numismatists have discouraged the practice of cleaning and chemically altering a
Causes of Toning
From the moment a coin is struck, its metal begins to reach to its environment.
Over time, that environment can either protect or destroy a coin’s appearance. Every
factor, from the coin holder to the humidity can impact a coin’s surface. Toning
may occur to coins of any metal, but is often particularly prominent for brass,
bronze and silver coins.
- Exposure to salt water corrodes a coin’s surface, so its appearance may look pitted.
- Long-term use of PVC-containing flips can irreversibly discolor a coin.
- Older coins are more susceptible to damage due to storage containers. Even the
tissue paper the US Mint once used to wrap Proof coins causes discoloration.
- Excessive heat can actually melt coins, dulling the ridges and high points.
Because many kinds of toning occur naturally as a coin ages, avid collectors actually
prefer toned coins. Since this discoloration can increase a coin’s value, many dealers
will attempt to replicate these effects to make coins appear to look like a Rainbow Toned Morgan Dollar.
Signs that a Coin Has Been Artificially Toned
Especially for new collectors, it can be difficult to spot the signs of artificial
toning or cleaning. The PCGS refuses to grade coins whose surfaces have been altered
by physical methods or by adding substances to the surface.
- Hairline scratches on the coin’s surface indicate cleaning with an abrasive chemical
- A dark brown or bluish hue often comes from chemical toning.
- Spots often appear on an artificially toned coin’s surface if the chemical reacts
- Toning achieved by application of heat or chemicals usually lacks depth and gains
more pastel hues.
- Sulfur compounds grant more natural hues, but the colors tend not to blend well.
- Splotchy or uneven coloring usually results from a poorly executed artificial
- Tab toning, a particular kind of discoloration due to a vintage coin holder, most
often occurred on commemorative half dollars from the 1930’s to the 1950’s. Other
coins with tab toning are unlikely.
- On Proof and Mint State coins, dealers may add artificial toning where the natural
toning appears to have rubbed off, usually on the coin’s high points.
- A process known as “hazing” or “smoking” involves exposing the coin’s surface
to cigarette or cigar smoke, which cover defects with an opaque film.
- Application of “nose grease” (skin oils) temporarily masks hairline scratches,
but later causes the surface to turn brown and splotchy.
- Auto-body putty is often applied to
Morgan silver dollars to cover blemishes, but leaves an easily detected film
or frost on the coin’s surface. Used for the same purpose, dental wax is more difficult
- Known as “whizzing,” the process of mechanically moving surface metal adds an
- Torches may be applied to melt a coin’s surface and obliterate defects like hairline
scratches. On gold coins,
this treatment can cause an “orange-peel” effect.
Often artificial toning can lead to discoloration that worsens over time. Chemicals
may continue to react with the coin’s surface long after the chemical appears to
have been wiped away. With practice, any coin collector can learn to identify the
effects of artificial toning and protect themselves against unscrupulous coin dealers.
This information is provided for general reference purposes and does not constitute
professional advice. For detailed coin collecting or investing information, please
consult with a professional expert.