Die-sinking, the art of engraving the die or stamp used for striking the impression on coins and medals, and for stamping thin plates of metal into various shapes. The method of sinking the dies used for coins or medals will serve to illustrate the general method of die-sinking. Suppose the coin to be of the size of a shilling: a cylindrical piece of carefully selected steel, about three or four inches in length, and two in diameter, is prepared by slightly rounding one end of the cylinder, then turning and smoothing upon the middle of this a flat face equal to the size of the coin. This blank die, which is carefully softened by the process of Annealing (q.v.), is then engraved with the device of the coin in intaglio. This is a very delicate and artistic operation, and is effected by a great number of careful touches with small and very hard steel tools. The face of the die is now protected with a thin coating of lampblack and linseed-oil, and then placed with its face downwards in a crucible containing animal charcoal. In this position it is raised to a cherry-red heat, then taken out, and hardened by being plunged into water. When properly tempered, it is in a state to be used for stamping the coin; but dies of superior workmanship, from which many impressions are required, are not thus directly used, as the expense of engraving is very great, and the risk of breakage considerable. This first engraved die, called the matrix, is therefore reserved only for making other dies. An impression in relief is made from this matrix on a small block of soft steel, which is called the puncheon; this is retouched and hardened, and from it the dies directly used for striking the coins or medals are impressed. When the engraving is not very costly, a small number of impressions required, or a soft metal is to be stamped, as in livery buttons, for example, the work is stamped directly from the engraved die or matrix. See MINT.
Die-engraving is a very ancient art, and was perhaps first suggested by the closely allied art of engraving gems. Notwithstanding the great number of ancient Greek coins which have been preserved, it is stated by Mr R. S. Poole, of the British Museum, that only one of the many dies which were used for these has ever been found, or at least only one believed to be of undoubted authenticity. The Greek coins struck between the years 415 and 336 B.C. show that the art of engraving dies had then reached the highest point of excellence which it ever attained either in ancient or modern times. As works of art, the Italian medals of the 15th and 16th centuries come next in merit to Greek coins, but none of these of the 15th, and only the smaller sized ones of the 16th century time were struck from dies. All the others were cast either from wax models or from patterns made in other materials. The art of cutting dies, in the comparatively deep intaglio required for medals, consequently dates from the beginning of the 16th century. Since then, or soon after it, Germany, France, Russia, and England, as well as Italy, have all had many more or less famous die-gravers.
The engraving of dies for medals is perhaps that branch of the art which gives the greatest scope for artistic skill, although the work on those required for coins is nearly identical in its character. Comparatively few dies of new design are, however, required for coins, while many hundreds of medal dies are annually made in England. The medals struck from these are used for such purposes as awards at exhibitions, colleges, and schools; for prizes at various games, and in commemoration of various events. Copper, bronze, and tin are the metals most commonly employed for medals, the copper being usually 'bronzed' on the surface. A copper medal with a head in moderately high relief requires half a dozen blows in the screw-press to bring up a sharp impression; but some in very bold relief require to be struck with as many as thirty blows. The medal requires to be frequently annealed during the process. Coins are finished at one blow, so that the devices upon them are only in slight relief. When a coin or a medal is being struck, a steel collar, accurately fitted to the die, is used to prevent the metal from spreading.
Dies have been extensively applied in Birmingham and other places to the manufacture of many kinds of objects in sheet-metal. These are of all sizes, from those required for parts of jewelry up to dies weighing more than a ton. Large and heavy dies are, however, cast, and only in some cases finished with the graver—those for such articles as curtain-pole and cornice ornaments being among the largest kinds worked up and finished with the die-cutter's tools. Dies have recently been used in America in the stamping or pressing of solid pieces of wood into lion's heads, rosettes, and other ornaments, in high relief, to imitate wood-carving. By the same process similar ornaments, in bas-relief, are made in pieces of wood formed of several layers of veneers.