A good place to start learning about ancient coins is to first learn how they were made.
One thing that many new ancient coin collectors comment on is the fact that no two coins are exactly alike. Some are more round than others, some have cracks or splits, and many are slightly (or very much) off-center. Because the coins were all struck by hand, each coin is different from all others.
The mint, in ancient times, as well as today, was the central point for producing coins. Although the methods may have varied over time, or depending on the particular mint at which it was struck, the general procedures were similar.
Production of a coin started with the arrival of the metal from which the coin was to be struck. The metal would either be rolled into a sheet, and then stamped into round blanks, or poured into molds.
Most researchers seem to agree that the dies used to produce the coin were most likely created by first engraving a crude image into iron, which was then annealed, or heated and then allowed to slowly cool. This rough image was then stamped onto a working die, and was then finished by the celator, or die-carver, who would have used hand tools to add the fine details that would complete the die. This final carving would have been the most time-consuming task in the process, and would require the most skilled workers.
Once both dies (obverse and reverse) were completed, one would be mounted on an anvil, and the other on a hand-held punch.
In the production area of the mint, a number of workers, most likely slaves, would have been involved in the actual production of the coin. Some of the workers would have been responsible for heating the blanks in a forge to soften the metal for striking. Once the metal blank was hot, it would have been transferred with metal tongs onto the die face set into the anvil. The other die face, set into the punch, would be placed on top of the hot blank, and another worker would strike the punch with a mallet. Often, several blows would have to be struck to create the coin.
After the coin had cooled, it would have been bagged up with the other coins struck, and delivered to the Imperial treasury, from where they found their way into circulation.
The volume of coins produced by the mints seems to have been quite variable, depending on the needs of the empire. Estimates place the production of coins at anywhere from 1/2 million a month in the early days of the Imperial period, to upwards of 2.5 million a month. Obviously, the production of so many coins would have required a huge amount of manual labor, and at times, a frantic pace. One can almost imagine one of the shop foremen "encouraging" the workers: "C'mon, youse guys! Move it! We gotta get 1,000 more coins out the door before quitting time"!
With such a hurried pace, its no wonder that no two coins, even those struck at the same mint, on the same day, by the same workers, would be exactly like any other coin, and why collectors (and sellers!!) place more value on a well centered, well struck coin.
Di Hu has put together a great research project in the techniques of making Roman coins. Check it out....its worth the time : )
Minting Roman Coins A modern experiment in the techniques of minting ancient coins.
E-mail me at: Celator's Art@aol.com