After modeling the surfaces or figures in relief, if they are to be used on garden pottery, book-ends, vases, etc., or any design that has undercut surfaces, it should be covered over entirely with a one-half inch layer or blanket of wet clay or modeling wax. If the modeling has been done in clay it should remain overnight without the usual wet cloth over it, before placing this second clay layer. If wax is used the clay layer can be placed over it without waiting. Deep sections should be lightly filled with clay to reinforce the one-half inch layer. Two or three nails should be used to hold the original firmly to a board base. A little plaster-of-Paris should be poured around its base to help make it firm.
Over this clay blanket lay a strip of clay along the highest part or equator of the surface, so that the surface is directly in line with the equator. Place a casing around and fix so that plaster can be poured, and a rough casing produced of one half. Remove the clay strips and with a pointed piece of metal bore several holes or “keys” in the exposed edge of the plaster. Oil this edge and cast the second half.
Before pouring the plaster a clay cylinder should be placed at the top to form a hole for pouring into and a second hole near it for an air escape.
After the plaster is set it will be found that a casing or shell is produced which when placed over the original model (the one-half inch clay blanket having been removed) will leave a space around the entire original model.
The next step is to prepare the casings and pour the glue into this space to produce a mold of the object and its immediate surface.
A few pencil marks are made on the outside of the casing and carried onto the table or board base to check up its relation when it is replaced. These marks are very necessary.
The casings are then given two coatings of shellac and wood alcohol (one part alcohol, three parts shellac), and when dry are oiled well or greased with axle grease. Shellac is also applied to the original model whether clay or plaster. Plasticene or similar wax need only be oiled slightly.
Replace the cases so that the two halves come together closely and so that the marks on the outside lower edge correspond correctly with the marks on the table. Stop the cracks on the casing with clay dipped in plaster and bind over the casing in the same way (or with the use of cords) to prevent the glue from floating the casing.
THE GLUE IS PREPARED as follows: White fish glue or gelatine glue is washed well in water. Put in dry can, placing it in second pan of water and boil until creamy in consistency. When the finger can be dipped into it without burning, the glue is poured into the casing as follows:
A funnel of clay or wax is roughly made and the glue poured into the opening of the casing, filling the space between the model and the plaster casing.