Milled coinage

In numismatics, the term milled coinage (also known as machine-struck coinage) is used to describe coins which are produced by some form of machine, rather than by manually hammering coin blanks between two dies (hammered coinage) or casting coins from dies.

Introduction

Until 1550, coinage techniques used in European mints had not progressed from the hammered coinage of Ancient Greece. This was problematic because an increase in the supply of bullion from central Europe and America was overworking mints. That led to low quality coins which were easily forged or clipped, i.e. precious metal was shaved from the edges of the coins. In accordance with Gresham's law, the clipped and forged coins drove good coins out of circulation, depreciating the currency.

Leonardo da Vinci's notebooks showed there was a better way and Donato Bramante, the architect who made the initial plans for St. Peter's Basilica, developed a screw press to make the lead bullae attached to Papal documents. In 1550, the French ambassador to Augsburg, Charles de Marillac, saw a way for France to get an economic advantage over the Holy Roman Empire when he learned that a local engineer had perfected a mechanical process of rolling bullion to the required thickness, cutting blanks from the rolled metal, and striking coins from those blanks. This technology was significantly more advanced than the general manufacturing processes of the 16th century making the coins difficult to counterfeit.