(1) The model (of clay or otherwise) is first covered with a layer of good plaster of Paris mixed, or "gauged," as plasterers call it, to the consistence of batter, and coloured with a little red or yellow ochre. This layer should average about 1/4 in. thick. It is best applied with the pewter or metal spoon used to mix the plaster with. The plaster is mixed in a basin half full of water, into which it is sprinkled by the hand, as oatmeal is sprinkled in making stirabout; when the plaster reaches the surface of the water, it is about sufficient, but experience soon teaches the right proportion. The mixed plaster can be jerked by a dexterous twist of the spoon into the deep undercut places, and care must be taken not to inclose bubbles of nir. A practical moulder would place the clay slab in a vertical position, as he would see the process of his work better. A large model would require several mixings of plaster, as when the plaster begins to set or harden, it is useless for moulding. When the first coloured coat of plaster is hardened, a wash of clay-water should be applied nearly all over it, and the second coating, which may be of coarser stuff, put on to the thickness of about 1 in.

If the mould is very large, some strips of iron nail rod, 1/4 in. square, may be imbedded in the back of the mould to prevent warping. When the mould is set hard, it must be turned over, and the clay picked out. If the work has been modelled on a board or slate, or best of all, oh a plaster slab, it may be necessary to pass a wire between the clay and the board to separate them. When the mould has been well cleaned and washed with a soft brush, it should be soaked in a tub of water until quite saturated through and through, drained, but not wiped, and a sufficient quantity of superfine plaster, carefully mixed, poured into it, and, by moving the mould about, carefully distributed all over. This may be backed with coarser plaster, and strengthened with iron rods, which in this case should be painted or coated with a varnish of rosin and tallow. When the cast is set hard, the most difficult part, called " knocking out," begins. A light mallet and a carpenters' firmer chisel, by a few dexterous strokes applied upon the edge, will separate the coarse outer backing of the mould, prevented from the wash of clay water from adhering to the first coloured layer.

The cast should then be placed upon a soft elastic bed - an empty sack folded is as good as any - and by gentle taps, holding the chisel perpendicularly or nearly so, to the face of the work, the coloured plaster may be snapped off, sometimes in large, sometimes in minute pieces, the colour preventing the operator chipping away the best part of his work, which may happen when mould and cast are of one colour. A chisel 1 in. or more broad may be used for the first rough work; smaller will be required for delicate parts.

A figure in the round may be moulded by the same process, but the mould must be in two parts. A strip of clay 1 in. or so wide must be fixed all round the clay figure, to be removed when the first half of the mould is done. The edge of the first half must have sunk holes, made by any convenient steel modelling tool, to ensure the fitting of the two halves of the mould. Projecting limbs must be cut off with a fine wire, and cast separately. If an iron support enters the back of the model, a little clay must be put round it, close to the model, to enable the iron to be drawn through the mould, and the hole in the mould stopped up with plaster. The two parts, carefully saturated and bound together, may be about half-filled with well-mixed superfine plaster, as thick as cream, which, by carefully turning and inclining the mould, cau be made to cover the whole of the mould, leaving a large hollow to be filled with a coarser plaster, in which a painted iron rod may be inserted. Good plaster smells sweet, sets in 10-20 minutes as hard and as crisp as loaf sugar. Bad plaster smells of sulphur, and never sets hard.

Beginners must make sure of their materials, and even then should try their hands on unimportant work.

Small reliefs may be moulded in wax. A border of clay or strips of wood a little higher than the highest part of the model must be fixed all round, and melted beeswax with a little rosin and tallow added, poured over the clay. When the wax is cold, and the clay well washed out, superfine plaster can be poured in as into a plaster mould. The wax is afterwards melted off or softened before a fire and peeled off, to serve again as often as you please. Hands and arms, and legs and feet, can be easily moulded in plaster, care being taken to grease or oil the skin well. The outside of the moulds may be deeply scored before the plaster sets, so as to break off in convenient pieces for putting together again.

In taking the cast of the face of a living subject (or victim), he or she should be placed sitting in a chair as if about to be shaved; the skin carefully greased, the hair and eyebrows smoothed down with clay or soft soap and superfine plaster, slightly coloured with ochre, mixed in warm water, dexterously splashed over the face with a silver spoon, care being taken to leave the nostrils free. The mould should not be quite 1/4 in. thick, and may be broken off in two or three pieces, which can be afterwards joined.

(2) To Prepare Plaster Of Paris

Immerse the unburnt gypsum for 15 minutes in water containing 8-10 per cent, of sulphuric acid, and then calcine it. Prepared in this way it sets slowly, but makes excellent casts, which are perfectly white instead of the usual greyish tint.

(3) Transparent Casts

Beautiful semi-transparent casts of fancy articles may be taken in a compound of 2 parts unbaked gypsum, 1 of bleached beeswax, and 1 of paraffin. This becomes plastic at 120° F., and is quite tough.

(4) To Toughen Casts

Immerse in a hot solution of glue long enough for the mass to be well saturated. They will bear a nail driven in without cracking.