Harper's indoor book for boys

by Joseph H. Adams

A simple method of doing this is to take an ordinary school slate and make the outline of a head on it. Within this outline you build up roughly with your finger and thumb a cake of clay about half an inch in thickness; then with your modelling instruments work it up as accurately as your artistic skill will permit (see Fig. 13).

When in the progress of your work you find it necessary to leave it for a short time, be careful to cover it over with a wet cloth, and if for a long time, put two wet cloths over it, and cover them in turn with a sheet of newspaper. This is necessary to keep the clay from getting hard and unfit for working. If at any time you find the clay getting too stiff, sprinkle it with water shaken from a whisk-broom. To make the moulds of your clay model you will require a little plaster of Paris, some lard oil, and some soap, and then your outfit is complete.

When your clay medallion is finished, build a wall of clay around it of about an inch and a quarter in height, as shown in Fig. 13; then get a teacupful of lard or olive oil, and add to it a good teaspoonful of any kind of soap scraped fine. Put this on the stove and stir until it is thoroughly mixed; then with a soft camel’s-hair brush lay a slight coat over your entire work.

You must now mix your plaster. If the surface of your medallion is, say, one foot by six inches, you will require about two pounds of plaster to about a quart of water. Sprinkle the plaster into the water, and then watch it until bubbles have ceased to come to the surface. When no more bubbles appear, stir it up well with a stick. The mixture should be about the consistency of thick cream. The exact proportions you must find out by experiment. This plaster cream you pour quickly over your medallion, blowing gently with your mouth on the fluid as it spreads itself over the face of your work; this is to prevent the formation of bubbles. In a short time the plaster will become hard; you then remove your clay wall, and lift the plaster mould, or matrix, from the clay. This you do by passing a penknife all round between the plaster and the slate, after which it lifts easily. You have now a perfect plaster mould. If you find any small particles of clay adhering to it, wash them off with a soft camel’s-hair brush and water.

You now want to get a plaster cast from your matrix. To do this you lay a coat of the soap and oil mixture with a camel’s-hair brush all over the face of the mould, and then pour in the plaster just as you did before, taking the same precautions to blow upon the plaster and to build a wall of clay around the mould.

You let this stand for half an hour until it is perfectly set, when you can remove your casting by passing a thin-bladed knife all round between the matrix and the casting. If it does not then lift easily, plunge the whole thing in water for an instant, after which you will have no difficulty in separating the two parts.

You now have a plaster cast of your original work, which you can touch up and finish off with sand-paper, or with the blade of a penknife if necessary.

You can, of course, make as many casts as you please from your mould, and thus have very pretty little souvenirs to present to your friends.