A Fake is a counterfeit coin made of the wrong metal (a metal that is less valuable than the metal the coin is supposed to be made out of). For example, you buy what you think is a 1 ounce Eagle, only to find out that it is a counterfeit made of bronze. A Copy is a counterfeit coin that is made of the proper metal.
Copies are not very important to bullion collectors, since they contain the proper content of the metal of the coin. Few people would consider making a counterfeit coin made of the proper metal unless they could make a big profit. Therefore, most (if not all) counterfeit "copies" are made of rare coins (such as the St. Gaudens coins), where the value of the coin is a lot higher than the gold content. I have no idea how you would spot a copy.
Fakes, on the other hand, pose a problem for bullion coin collectors. Since the majority of the price paid for gold (or other precious metal) coins is for the value of the metal, a fake coin is nearly worthless. However, they are much, much easier to detect than copies.
Gold and platinum are very dense (heavy) metals. The few metals as heavy as gold and platinum are either expensive or hard to work with. Therefore, a fake will almost certainly be made with a much lighter metal. This means that one of two things will be wrong with the coin: Either it will be too light, or it will be too big.
Because of this, it is relatively simple to catch a fake gold or platinum coin. First, you weigh it with a reasonably accurate scale (remembering that a 1 troy ounce gold coin can weigh from about 1.1 to 1.2 avoirdupois ounces, depending on the fineness). Then, you measure it (the width would almost certainly be the correct width, but the height of a fake would be different). If the weight or size is wrong, you've got a counterfeit coin. Note that this does not necessarily hold true for silver coins, as lead is denser than silver. However, if a silver coin weights less than it should, it is almost certainly a fake.
For a device that easily does the job of detecting a fake, you can check out the Fisch Instruments web site. It also explains in more detail the process of detecting fakes.
In the United States, it is illegal to sell counterfeit coins unless the word "copy" is engraved on it. So, you should also look out for that on any coins.
This page last updated April 30, 2006 .