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Stamping

die, metal, medals, relief, dies and impression

STAMPING.

The most ancient and familiar application of dies, is in the striking of coins and medals; the method of sinking the dies used for this purpose 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 steel, about 13 or4 in. in length, and 2 in diameter, is prepared by slightly rounding one end of the cylinder, then turning and smoothing upon the middle of this a flilt face equal to the size of the coin. This blank die, which is carefully softened, is then engraved with the device of the coin in intaglio. This is a very delicate and artistic process, and is effected by a great number of careful touches with small and very hard steel tools. The face of the die is now hardened by placing it face downwards in a crucible upon a layer of bone-dust, or a mixture of charcoal and oil. In this position it is raised .to a cherry-red heat, then taken out, and plunged iu 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 steel, which is called the puncheon; this is retouched and hardened, and front 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 aamped, as in livery buttons, for example, the work is stamped directly from the engraved die or matrix. When the device is in high relief, and the metal is hard, many heavy blows are required. Some of the finest large bronze medals require 200 or 300 blows for each impression, and the medal has to be annealed by heat ing between every 2 or 3 blow's. It is on this account that the difference between the

price of pewter and bronze medals of the same subject is so great, the pewter being so much softer. Copper, though harder titan pewter; is much softer than bronze, and hence the reader will easily understand why the device on the new bronze coinage, manufactured at the new mint of Birmingham, is in much lower relief than the old cop per coinage, as it would not pay to use repeated blows and annealing in striking com mon coins. An impression in high relief or deep intaglio may be obtained by a single blow by the cliché method. For this, a fusible alloy is used, such as type-metal, or still better, an alloy of 2 parts bismuth, 1 lead, and 1 tin, which fuses at about 212°, and becomes pasty before solidifying. The metal is poured into a box or tray a little larger than the die, and when in a pasty condition, the die is placed over it, and struck smartly with a heavy mallet or a coining-press. A steel die is by no means necessary for this; sharp impressions may be obtained from bronze medals themselves, or even from wood and plaster casts. A cliché mold may be made in the first instance from the medal, and then a cliche relief from this mold, if the process is skillfully conducted. The skill required consists mainly in striking the blow with a force proportionate to the depth of the impression and the softness of the metal, and in selecting the right mo ment for doing so, just as the fused metal is on the point of solidifying; for, if too fluid, it will merely be driven aside; and if at all set, an imperfect impression results. The metal should be of about the consistence of melted sealing-wax, and then the surface is set by contact with the cool die or medal, while the body of the metal still yields to the pressure. Cliche molds arc admirably adapted for electro-depositing.