A planchet is a disc of metal which has been prepared for stamping as a coin, but not yet stamped. Planchets are sometimes called “blank coins.” These little metal discs are produced in vast numbers either in mints or facilities which mints contract with to make blanks. Occasionally, an error happens during coin production and a blank planchet is mistakenly put into circulation; such blanks can be valuable, depending on the coin involved.
The terminology which surrounds planchets is a bit murky. Officially, a flat metal disc which has been machined is considered a blank. When the blank has been stamped to create a raised edge, it becomes a planchet, prepared for stamping with the imprint of a coin. Once stamped with the coin die, the disc becomes a coin. A blank or faint planchet is a planchet which was not struck by the die or was struck by a misregistered die which left only a faint impression.
When discussing ancient coins, the term “flan” is used to describe a blank. However, in practice, the term “planchet” is often used whether one is talking about a true planchet, a blank, or a flan, which can sometimes be a bit confusing. Flans were made by casting, rather than machining, and tend to have more irregularities as a result.
Planchets are made by rolling out a sheet of metal to a uniform thickness and stamping it with a cutting die which punches out a number of discs. The discs at this point have somewhat rough edges and usually have a cloudy color, as well. When the blank is stamped to turn it into a planchet, the creation of a raised rim also smooths the edges. The blank planchets are then fed into a die press which stamps the blanks with the impression of the coin and adds the distinctive reeded edges found on many coins.
Mints usually try to keep errors out of circulation, but they are occasionally released, and they may become hot objects for collectors. A planchet is visually interesting, but can be hard to verify, which is one reason why planchets are usually not very valuable. One could potentially counterfeit a coin blank with the right equipment. It is important to note that since most mints add reeded edges at the time that coins are struck in the die, it is not possible for the surface of a planchet to be blank and the edges to be reeded. This can only happen as a result of abnormal wear or deliberate manipulation of the coin.