B. When metal is beaten thin, it becomes what is technically called 'plate,' (the _flattened_ thing,) and may be treated advisably in two ways: one, by beating it out into bosses, the other by cutting it into strips and ramifications. The vast schools of goldsmiths' work and of iron decoration, founded on these two principles, have had the most powerful influences over general taste in all ages and countries. One of the simplest and most interesting elementary examples of the treatment of flat metal by cutting is the common branched iron bar, Fig. 8, used to close small apertures in countries possessing any good primitive style of ironwork, formed by alternate cuts on its sides, and the bending down of the severed portions. The ordinary domestic window balcony of Verona is formed by mere ribbons of iron, bent into curves as studiously refined as those of a Greek vase, and decorated merely by their own terminations in spiral volutes. All cast work in metal, unfinished by hand, is inadmissible in any school of living art, since it cannot possess the perfection of form due to a permanent substance; and the continual sight of it is destructive of the faculty of taste: but metal stamped with precision, as in coins, is to sculpture what engraving is to painting. 158. Thirdly. Stone-sculpture divides itself into three schools: one in very hard material; one in very soft; and one in that of centrally useful consistence. [Illustration: FIG. 8.] A. The virtue of work in hard material is the expression of form in shallow relief, or in broad contours: deep cutting in hard material is inadmissible; and the art, at once pompous and trivial, of gem engraving, has been in the last degree destructive of the honor and service of sculpture. B. The virtue of work in soft material is deep cutting, with studiously graceful disposition of the masses of light and shade. The greater number of flamboyant churches of France are cut out of an adhesive chalk; and the fantasy of their latest decoration was, in great part, induced by the facility of obtaining contrast of black space, undercut, with white tracery easily left in sweeping and interwoven rods--the lavish use of wood in domestic architecture materially increasing the habit of delight in branched complexity of line. These points, however, I must reserve for illustration in my Lectures on Architecture. To-day, I shall limit myself to the illustration of elementary sculptural structure in the best material,--that is to say, in crystalline marble, neither soft enough to encourage the caprice of the workman, nor hard enough to resist his will.