This section is from the book "Spons' Mechanics' Own Book: A Manual For Handicraftsmen And Amateurs", by Edward Spon. Also available from Amazon: Spons' Mechanics' Own Book.
Some metals, especially copper and block tin, lend themselves so well to hammering processes, and manifest such a tendency to assume various bent forms without either creasing or cracking, under the influence of repeated blows judiciously delivered, that this is the general way of working with them. The piece of sheet metal of the required size is placed on the mould whose form it is to acquire, and very carefully, gradually, and equally hammered till it assumes the desired shape. The metal appears to have the power of redistributing its constituent molecules, so that the portion expanded by the blows draws upon the unhammered parts and maintains a uniform thickness. A hemispherical bowl may be made in this way from a flat sheet by gradually beating it into the recess in Fig. 203 by means of the round end of the mallet. A dish with fluted sides may be formed from another sheet by hammering a margin of the same width as the desired sides in the hollows of Fig. 204, the bottom of the dish being subsequently flattened down by hammering a hard block on it. Obviously the process must be gradual and the blows equally distributed in order to secure symmetry in the finished article.
Highly ornamental work may be done with suitable moulds and dies; but in the case of copper, if the impressions are deep, the metal will require frequent annealing by heating it, as the blows or stamps rapidly render it brittle and liable to crack.
There is another kind of seamless work produced by a spinning process. The metal or rather alloy best adapted to it seems to be Britannia metal or pewter. A sheet of this metal is mounted in a lathe, either by drilling a hole through and screwing it, or by pinching it between wooden blocks. When fixed so that it can rotate freely, pressure is applied to the side of the plate by means of an oiled or greased burnishing tool with a smooth blunt surface, the curve in the sheet increasing as the pressure is augmented. In this way a circular cup is gradually produced without the least sign of a crease or inequality in the surface. By using sectional moulds capable of being taken to pieces, most complicated patterns, such as teapots, feet of candlesticks, etc, can be made, by gradually pressing the rotating metal till it tightly embraces the mould, which is then removed. More elastic metals may be used if duly annealed, provided they possess sufficient malleability.