How a coin is made - The Minting Process

15 October 2012

In the minting process a planchet (or blank) is held in a collar and struck by the die. The impact of the die forces the metal to flow towards the rim which then forms the raised edge of the coin. The coin has a raised edge to protect the devices (the images/writing on the coin) from excessive wear (as would occur if it were higher than the rim of the coin.) 


As you can imagine in the minting of a small coin like a 1/10 oz the rim height is difficult to control, given the size. The US Mint, as with all mints, has specifications for each gold and silver coin with tolerances - a plus and minus measurement within which each coin can measure. 


The Fisch is made to the mint spec plus the maximum allowed tolerance so therefore a coin right at that tolerance (or maybe a bit over) will be a tight fit. For example, the thickness of a coin may be specified as 2.21mm (+/- 0.13mm). This means that the coin could be from 2.08mm to 2.34mm thick. (0.13mm is about 5/1000th of an inch. A normal piece of copy paper is 0.10mm thick. 


Modern coins have been minted in the same way for over 450 years. Aside from the advancement in the equipment that allows mints to make thousands of every day coins in an hour, the process is the same one: A metal disk is held in a collar and stamped with force. 


With gold and silver coins care it taken firstly in the refining of the gold to the correct fineness and then ensuring that the blank is the correct weight. But in the turning of that gold or silver blank of an exact fineness and weight into a coin is not an exact science: The coins do not all come out the same size. The very process of stamping them out cannot be controlled exactly - hence the tolerances allowed in the specifications. 


Mints do spot checks but sometimes coins that are outside the tolerances - particularly the smaller ones find their way onto the market. The mint sees no reason for rejecting all but the obviously defective coins. They are what they say they are: a certain weight of gold or silver and of certain fineness. 


The important issue with gold and silver coins is that they start with a blank that is the correct weight and fineness. After all, you are buying gold or silver. Not coins, but gold or silver!