The plaster will set, or become hard, in a little while, and you then tear the box away, and take out the model and plaster together, leaving the first clay mould. Next put the plaster mould and model in a clay box just as you did before, and pour plaster over it, first greasing the model and upper surface of the mould. Before pouring on the plaster, roll a small piece of clay in your fingers, and put it on the model (Fig. 17), so that when you pour plaster over it, a hole will be left in it through which you may pour plaster for the final cast.
For the second time tear away the clay box, and gently separate the two parts of plaster of Paris; take the model out, and you will have two blocks of plaster, which, when brought together, will contain an exact mould of the model (Fig. 18), and one block will have an opening in it through which you can pour plaster. Before pouring in the plaster, however, be sure to grease the insides of the mould. Then put the parts together, using the pegs and holes as guides to a proper fitting, and tie firmly with a piece of twine. Now pour the plaster in, and then shake the mould gently in order to make the mixture settle in all the smaller crevices.
PLASTER-CASTING IN GENERAL
Fig. 18. Fig. 19. Fig. 20.
Of course when you separate the parts of the mould now you will have a perfect cast of your model. It will have a thin ridge running around it where the mould was joined, but that is easily rubbed off with sand-paper.
In a mould made from a hand you proceed in about the same way. The great thing is to find the dividing line in the model; that is, the place where the parts of the mould ought to join. In the egg it is easy enough, for you can divide it into two equal parts; but you take a hand, and you have to make the line around each finger just where it is broadest (Fig. 19), and build the clay up to that line. The wrist-hole in a hand-mould makes a good hole to pour the plaster in (Fig. 20), and, after all, a hand is easy to make.
These simple directions should make it easy for the amateur modeller to acquire the first principles of the art. There are several good compositions in which the young craftsman can work besides plaster of Paris, such as “Kiln Cement,” “Carton-pierre,” “Papier-maché,” “Plaster Compounds,” “Artificial Marble,” and “Concrete.”