Exploring Surface Textures
Posted by Skip Fazzari, Authentication Consultant to NGC, on 1/24/2008
The texture of a coin's surface provides clues to both how it was made and its state of preservation.For example, we can generally say that a die-struck coin will show some indication of metal flow.We can find other characteristics on a coin's surface due to its type, composition, and state of preservation.A vast array of surface textures will quickly become apparent to any collector at a major coin show. All we have to do is look.
Let's begin with Proof coins.One texture often associated with brilliant Proof gold struck before 1907 is called "orange peel" because of its uneven, flaky pattern. Proof gold minted in the early 1900s can be found with either a "satin" or "matte" surface.Under magnification, these coins have an etched, granular, or pitted surface. Fakers have tried to duplicate these experimental finishes by various methods such as sandblasting or pickling, but I cannot recall ever seeing a counterfeit coin displaying an orange peel texture.
Brilliant Proof silver and gold coins have the typically smooth mirror surface and sharp relief characteristic of this method of manufacture using polished planchets and multiple strikes.Fakers have tried to duplicate this surface by polishing mint state coins.
The surface of Proofs struck in nickel alloys runs the entire range from smooth mirror to matte.There are several dates in the shield nickel series whose coins may not appear to be Proof, yet Mint records indicate that only Proofs were struck for that year!
Business strike coins exhibit a wide range of surface textures depending on their age, composition, and coin type."Metal flow" lines are important here.They can be most easily found near a coin's rim unless it was struck with "fresh" dies.Genuine coins struck from worn dies will have grooved and rough surfaces often showing some granulation in the fields, and stretched out or outlined areas of relief.For the sake of simplicity, we'll leave circulated coins out of this discussion.Numismatists know that there is a relationship between the condition and texture of a coin's surface and the amount and type of luster it will have. As a result, we may see different types of luster found on coins described by terms such as "frosty," "dull," and "satin."
The similarities of surface luster between different coin series aid in detecting counterfeits.For example, electrotype fakes usually exhibit a "flat,” "lifeless,” uneven surface compared to the genuine item.Cast coins in all metals have a porous, granular surface with unusual luster. The porosity and texture is chiefly dependent on the method and quality of the casting and the time it took to cool.Authenticators must also be mindful of a coin's surface condition because a number of environmental factors or fraudulent alterations can make a genuine coin appear to be a counterfeit.Aside from wear from circulation, corrosion is probably the biggest natural enemy of a coin's surface.Improper cleaning and chemical or mechanical alteration are the greatest man-made factors affecting a coin's appearance, but even an overly dipped silver coin may look suspicious at first glance.Of course, those coins which are known to be counterfeited come under the closest scrutiny. This includes Commemorative Halves such as The Fort Vancouver and Hudson's Bay; Morgan Dollars dated 1896 and 1902; Twenty Dollar gold coins dated 1904, and 1924 to 1927; and the entire incuse series of Half Eagles and Quarter Eagles.A fairly complete list of known counterfeit and altered U.S. coins was published in Numismatist magazine a few years ago.
This article previously featured in Numismatic News.