In the production of very fine wire, the metal, after passing a few times through the draw-plate, requires annealing, as its fibres become so condensed and hardened that it is impossible to repeat the operation without some risk of the wire breaking. For fine wire the annealing is repeated five or six times during its passage through the draw-plate; for stouter kinds the annealing need not be so frequent. This process produces a scale or oxide upon the surface of the wire, which should be removed before the continuation of the drawing takes place, which is generally done by an immersion for a time in very dilute sulphuric acid pickle; or its passage may be assisted through the draw-plate by the application of some lubricating substance, such as beeswax, or a mixture of beeswax and oil, which enables it the more readily to pass through it. In the progress of the wire-drawing the holes have a tendency to become enlarged; these are made smaller again, by repeated blows upon the front of the plate with a somewhat pointed hammer ([Fig. 28]), and then opened from the back with a tapered steel punch, such as is shown in the woodcut ([Fig. 29]). The hardening and tempering of the punch is of importance. A gauge-plate is used in all establishments for the purpose of determining the size of the wire. The hammering should not take place upon a hardened draw-plate, as it would fly to pieces: it is only those known as soft which should receive such treatment; and those, by a continual alteration of the holes, gradually become hard and require annealing at intervals.
Fig. 28. Knocking-up Hammer.
Draw-plates for wire-drawing purposes are mostly cylindrical in form, but they are employed in various degrees of fineness and in different shapes; such as oval, oblong, half-round, square, fluted, star, sexagon, triangular, and other complex sections, for the production of corresponding wires, all of which receive similar treatment to that above described.
Fig. 29. Round Steel Punch.
The process of wire-drawing, in connection with the art of the silversmith, is more particularly employed in the manufacture of chains, in which branch a very large quantity of silver is consumed. This branch of the craft is almost a purely mechanical one, but, nevertheless, there are some designs in chains which require a considerable knowledge of art for the proper execution of them. It is, however, in “wrought” or hand-made work that true art is made to play so conspicuous a part; for it is here that perfect workmanship, together with great skill and taste, are required in the manufacture of an article. “Wrought” work was one of the earliest productions of the goldsmith and silversmith, and it still remains the true artistic method, although it has been superseded by others of a less expensive character; such as stamping, chasing, engraving, enamelling, casting, &c., to which the older processes of ornamentation and decoration by means of hammering have given place.