Fig. 13
The shape is now placed on the lathe and the bottom waste turned off, the base of the shape being slightly hollowed. The creator having arrived so far successfully may now unbend and scratch his mark on this new surface before well waxing it.
Dowels are cut in the waste of the two halves as shown, the fresh parts soaped, all fitted together and slightly oiled, then boxed in as in D and E, Fig. 13. Plaster about 2” thick at the thinnest part is poured on and the mould is complete. When set, the shape is removed and the three parts trimmed on all the outside edges. (Fig. 14.) The three pieces are assembled, firmly tied up to prevent warping, and thoroughly dried.
If preferred, the mould can be made cylindrical instead of square. This will give a more even suction to the slip and may be worth the extra trouble. For casting purposes a refractory clay containing a good percentage of China clay, maturing at about 03-01 but remaining perfectly white and porous, will be required.
Slip for casting is made thus: Clay, picked or broken into small pieces, is thrown into a bucket of warm water well slubbed up by hand and passed through a fine sieve (No. 80) with the aid of a stout
brush and thinned to the consistency of thick cream. This should be matured for some days, frequently stirred, and again sieved before using. For very small or fragile shapes, a finer sieve (120) is advisable. The mould, quite dry and clean, is now slightly moistened with a scrupulously clean sponge and water, the parts assembled, corded, and firmly wedged, leaving the top free as in Fig. 15. The slip, thoroughly stirred, is poured in very gently to avoid bubbles. With awkward moulds, a tube or funnel should be used to prevent splashing. If the mould be placed on a whirler and turned to and fro, it will prevent the heavier matter in the slip settling too quickly.
Fig. 14
As the slip sinks in the mould, the subsidence being due to the absorption of the water by the plaster, the mould should be continually filled up. After a few minutes the mouth is scraped free to test the deposit. When this is thick enough, varying, of course, with the size of the shape, the slip is poured out into another bucket. An unorthodox but often useful trick for strengthening long necks is to slide a piece of glass over the mouth and reverse the mould for a minute or so. The neck full of slip thus allows a slight extra deposit on the part that most needs it when we come to finishing off the lip.
