The modern methods of coinage that surfaced in fifteenth-century Italy probably owe their origin to Leonardo da Vinci, who spent time at the papal mint during a stay in Rome. In The Notebooks of Leonardo Da Vinci can be found the following references to the coinage of money:
All coins which do not have the rim complete, are not to be accepted as good; and to secure the perfection of their rim it is requisite that, in the first place, all the coins should be a perfect circle; and to do this a coin must before all be made perfect in weight, and size, and thickness. Therefore have several plates of metal made of the same size and thickness, all drawn through the same gauge so as to come out in strips. And out of these strips you will stamp coins, quite round, as sieves are made for sorting chestnuts; and these coins can be stamped in the way indicated above; &c. The hollow of the die must be uniformly wider than the lower, but imperceptibly. This cuts the coins perfectly round and the exact thickness, and weight; and saves the man who cuts and weighs, and the man who makes the coins round. Hence it passes only through the hands of the gauger and of the stamper, and the coins are very superior.
Leonardo’s technique brought a measure of precision to the coinage of money that had eluded even the best goldsmiths and silversmiths before the time of the Renaissance. The old method produced irregularly shaped coins that easily fell prey to clippers who could remove a bit of the precious metal without leaving any tell-tale signs. It began by casting precious metal in sand to form ingots roughly equal to the desired thickness of the coins. The ingots were reheated and hammered closer to the desired thickness. Then they were cut into squares, trimmed and weighed, and reheated. The squares were then hammered into a circular shape. Rolls of these blank coins were hammered into some degree of uniformity, making it possible to stack the coins. A hammer and a die struck the desired design on these blank coins to complete the finished product. The lack of uniformity in the coins made it easier for forgers to pass off inferior coins, and the whole process was a slow method for striking coins.
Leonardo’s contribution to coinage was the work of Leonardo the mechanical engineer, rather than Leonardo the artist. During the Italian Renaissance, however, the minting of coins engaged the talents of the best artists of the age. Some of the coins, minted by famous artists and distinguished for their beauty, became collectors’ items and sold for high prices. The famous Renaissance artist, Benvenuto Cellini, perhaps the most celebrated goldsmith in history, wrote a chapter in a treatise on goldsmithing and sculpture entitled “How to Make Steel Dies for Stamping Coins.” With respect to one coin he struck for Pope Clement VII, Cellini wrote: “This coin brought me much honor, for I put great labor into it.” The methods perfected by the Renaissance artists spread to France, and from France to Germany and Spain.