One point we have omitted to mention in our description of the Chelsea-Derby vase at South Kensington. The handles, winged figures somewhat classically treated, are of unglazed ware. This is an example of the famous Derby biscuit, or bisque, as it is sometimes called, which we now know was made as early as 1771. The greatest care was taken in the preparation of this biscuit ware; any piece with the slightest defect was rejected. The material allows of a sharpness and high finish which would be lost in the thick covering of the glazed ware. The paste in many of the examples has acquired a somewhat shiny surface, as if covered with a skin of glaze. The best known specimens date from the last years of the century, when Spengler, a modeller from Zurich, was engaged by the second Duesbury. In them we see exemplified that mixture of the sentimental and the pseudo-classical so much admired at this time. The shepherd with his dog (there is an example at South Kensington) is taken from a Roman relief, the head perhaps from an Antinous. The shepherdess has been reading Richardson, if not Jean Jacques, and they both take life very seriously. We find, however, the Chelsea-Derby mark on enamelled figures that differ little from the earlier and more frivolous type. These survivals, as it were, of the rococo school stand no longer upon a scroll pediment, but on a rocky ground, amid careful reproductions of natural objects, stumps of trees, shells, or what not. The colours, too, have become somewhat stronger; the pale, greenish blue of the earlier pieces is replaced by a fuller turquoise hue. It was at this time, or a little later, that the process of ‘casting’ was introduced for these statuettes. This was a process of English origin, though it is now extensively used at Sèvres and elsewhere abroad. We have described the various modifications of this plan in a previous chapter (p. 25). In the case of these statuettes, the figure is first modelled in tough clay; the head and limbs are then cut off. A plaster-of-Paris mould is then made of each of the separate parts, a cream-like slip is poured into the mould and quickly poured out before all the water is absorbed, a layer of the paste remaining on the sides of the mould. This layer is detached when sufficiently dry; the pieces are then joined together by means of the same slip, and the outline of the figure sharpened with a modelling tool.[234] Porcelain made by this casting process is not so dense as that made on the old system; its specific gravity is appreciably lower. The moulding or repairing knife may be, to some extent, replaced by the use of a brush, but a less sharp outline is obtained in this case. In the furnace these figures have to be supported by an elaborate scaffolding of props, and the shrinkage of the clay during the firing is another source of difficulty.