Piece-casting of large subjects, where the various parts are cast and then fitted together afterwards, is best understood by learning a little from some Italian modeller, or looking over the seams (representing the "piece-casting" joints) in some one or other of Brucciani's reproductions, which may be seen in almost any art gallery or museum.
One great advantage of this system is, that by its means large models, if built up in ordinary field clay, or by any other means, may be cast from in plaster or in metal by the intervention of piece moulds, failing which it would be impossible to do so. The resultant model, if in plaster, is not cast solid, but is hollowed out in the casting — to prevent weight — by "cores" being inserted in the moulds. "Casting sand" is, however, necessary when casting in metal, together with all sorts of technical appliances and knowledge beyond the scope of the taxidermist, and although I have found it necessary to cast in metal for some purposes, it is so seldom needed that I do not purpose describing what any friendly brass founder will tell the amateur in a few minutes. The casting by amateurs at an ordinary fire is limited to three metals — lead, tin, and zinc — or a mixture of two.
How large models in clay, etc.., can be made is described by Mr. Waterhouse Hawkins, F.G.S., etc.., in his paper on the reproductions he made of the extinct animals exhibited at the Crystal Palace, Sydenham:
"By careful study of their works I qualified myself to make preliminary drawings, with careful measurements of the fossil bones in our Museum of the College of Surgeons, British Museum and Geological Society. Thus prepared, I made my sketch-models to scale, either a sixth or twelfth of the natural size, designing such attitudes as my long acquaintance with the recent and living forms of the animal kingdom enabled me to adapt to the extinct species I was endeavouring to restore.
"I caused the clay model to be built of the natural size by measurements from the sketch model, and when it approximated to the form, I, with my own hand in all instances, secured the anatomical details and the characteristics of its nature.
"Some of these models contained thirty tons of clay, which had to be supported on four legs, as their natural history characteristics would not allow of my having recourse to any of the expedients for support allowed to sculptors in an ordinary case. I could have no trees, nor rocks, nor foliage to support these great bodies, which, to be natural, must be built fairly on their four legs. In the instance of the iguanodon, it is not less than building a house upon four columns, as the quantities of material of which the standing iguanodon is composed, consist of 4 iron columns, 9 ft. long by 7 in. diameter, 600 bricks, 650 5 in. half-round drain-tiles, 900 plain tiles, 38 casks of cement, 90 casks of broken stone; making a total of 640 bushels of artificial stone. These, with 100 ft. of iron hooping and 20 ft. of cube inch bar constitute the bones, sinews, and muscles of this large model, the largest of which there is any record of a casting being made."
Other uses of plaster are also described in Chapters VI. and VII. One of the uses of plaster in modelling is, however, to reproduce flesh, etc.. For this purpose mix plaster of Paris (best S.F.) with boiled oil until it forms a smooth, thick putty, which, though at first capable of much finger-and-thumb manipulation, dries as hard as stone, and is fairly light and impervious to damp. Plaster will also make a putty if mixed with glue-water.
The composition used by the picture-frame makers is also a first-rate medium, being susceptible to the softening influences of hot water when newly made, but ultimately dries as hard as the preceding. It is made variously, but perhaps the best is made thus:
Cement for Modelling.
Three parts best glue.