Fig. 13. A, bottom of case. B, Cavity for pouring molds. C, top of case.
The back of the plate mold and the edges of the block are now sized and plaster is run to the level of the highest part of the mold but no higher (Fig. 13). When this is set, the two halves of the case can be separated and the mold taken out. Now when the halves of the case are fitted together there will be a cavity the exact size of the mold. This can be filled again and again with plaster, a new mold being formed each time.
Fig. 14. Iron prong to fit wheel head.
Fig. 15. A, plaster, with prong inserted. B, rubber belt.
In order to use these molds a special head must be provided for the wheel. The regular head of the wheel should be detachable and in its place an iron frame called a prong is fitted. This consists of a collar either with a hollow cone or a screw to fit the shaft of the wheel, and from this radiate four short arms. In order to use this a circular block of plaster some two or three inches thick is poured on a table or slab and just as this is setting, the prong, upside down, is pressed into it just below the surface and held there until the plaster is hard enough to support the weight of the iron. When hard, the whole is lifted and the prong with the plaster attached is set in position on the wheel. This now forms a rough plaster head and it must be turned true. In this head a circular depression is to be turned which will exactly fit the back of the plate molds. If the recess should wear larger as it will if much used, a new head can easily be run. The same principle can be applied to the making of molds for saucers.
Fig. 16. Wheel head with plate mold. The tool used is shown in dotted outline.