With very few materials and little special knowledge you can make a great variety of useful and decorative articles from clay. The new self-hardening clays arc easily formed into vases, bowls, tiles, ash trays, book ends, flower holders, candlesticks, and human and animal figures. Even pottery making is now within reach of the beginner.
Plastelinc is the easiest clay to use and is excellent for practice where permanence is not required. It never hardens and may be reused many times. A little carbolated vaseline mixed in thoroughly will make it sanitary. Plasteline may also be used by the advanced worker for molds in producing plaster or clay reliefs.
Where permanent objects are desired, it is best to purchase one of the commercial self-hardening clays. Regular pottery clay must be baked in a kiln at a very high temperature to make it durable, although there is now a modified type which hardens in an oven in 15 minutes at 250° F. The self hardening clays, however, will set without cracking if they arc permitted to dry out gradually in a room of normal temperature. They may be kept plastic for as long as necessary by covering with a damp rag until the work is completed. Because they are easy to handle, require no special equipment and yield thoroughly satisfactory results, the present chapter deals only with this type.
There are a few terms that should be known to everyone who models. Clay is said to be "wet" when it is right for working. It should be puttylike in consistency and should not adhere to the fingers or crack when molded. Clay is "moist hard" when there is no moisture on the surface. Handles and spouts are put on at this consistency. Clay is said to be "leather hard" when a certain amount of moisture has evaporated from it. It is lighter in color and small pieces scratched from the edge will curl slightly. When .clay is still drier it is said to be "white hard." In this form surface particles come off in a fine powder when the clay is scratched or scraped.
"Slip" is liquid clay of about the consistency of cream and is used to attach one piece to another. It is made by filling a mixing bowl full of water and pouring in the dry powdered clay until the water will not absorb any more. The mixture should be stirred thoroughly and passed through a fine sieve to eliminate lumps. Slip may be stored in a glass or earthenware jar with about 1/4 inch water on the surface to retain the moisture. Wet clay must be kept in a noncorrosive container, covered with a damp cloth and stored in a cool place if possible.
Clay modeling requires little equipment. The work table should be covered with oil cloth or linoleum, since clay sticks to wood. Use a separate, movable base, or "bat," on which to build each piece. It can be wood, cardboard, or any stiff material. Other tools should include a sponge or soft cloth for smoothing the surface when the clay is damp; some fine sandpaper for smoothing when the clay is hard ; a knife; a few modeling tools (see instructions for modeling a clay figure), and some tin cans in which to mix the clay and keep it moist.
The coil system of building pottery is the simplest way of forming round or cylindrical objects such as vases or bowls. The first step is to make a profile drawing of the object about 10 percent larger than the finished product to allow for shrinkage. From this, a template or pattern is made by tracing one half of the drawing on a piece of cardboard and cutting along the line showing the outside contour of the vase (fig. 114).
The next step is to build the base. Roll out a large slab of clay about 1/2 inch thick and cut the base out of this (fig. 115). Use a pattern to guide your knife. Roughen the rim of the base by scratching it with any pointed tool. This is known as "checking" or "small cutting" and is done to make a firmer joint between bottom and sides.
The sides may be built up of either long coils wound in spiral form or short coils, each going once around the vase. The former method is the commonest and will be described here. From the same slab of clay, cut a strip about 1/2 inch wide. Roll this gently under your palms until it is a smooth coil. Bend the coil to make sure that the clay is wet enough; if it cracks, add more water. Make each coil just before it is to be used and moisten your fingers occasionally as you work.
To build the sides, taper the end of the first coil and weld it firmly to the roughened edge of the base. The joint may be cemented more tightly with slip. After the first coil is wound, join it to the second in the manner shown (fig. 116). Moisten and mold the two pieces together.
When the vase is about half built up, smooth the clay both inside and out by rubbing with the fingers (fig. 117). Use the template frequently to make sure that the vase is assuming the correct shape. Hold the template against the sides at numerous points and press the coils in or out as needed. Work with your fingers on both the inside and outside as you do the coiling.
When you come to the top, taper the end of the last coil and smooth all the coils of the upper half. Rest a piece of cardboard on the top to see if it is level. If necessary, add or remove some clay to even the rim. Slight irregularities can be smoothed with sandpaper after the vase is dry. A lid may be made in the same way as the base with a knob of clay added for a handle.