CHAPTER XIII: CASTING

In commercial production the casting method is constantly used. It is a means of making light and delicate pieces with ease and, of course, all the pieces cast in the same mold are alike. This very fact, however, has led to the method being disregarded by the studio worker who does not wish to duplicate anything that he makes. If a single piece only is to be made the work involved in molding is a waste of time and it is better to strive for skill at the wheel, and yet there are occasions when a knowledge of casting is of great value. In the preparation of trial pieces there is no method better. To make these in sufficient number on the wheel would be tedious except for the benefit of the practice involved.

Directions for making molds have already been given and the slip which will have been prepared in the process of clay making is ready for the casting process. This slip should be thick, about the thickness of buckwheat batter. To be accurate, a pint should weigh 26 ounces. For small pieces or for vases with narrow necks it is advisable to use the slip rather thinner. For large wares, on the other hand, or for open bowls it may be slightly thicker. A few experiments will show the reason for this. Two quart jugs are needed. They should be large of neck and should deliver their contents freely and completely. Jugs with a deep shoulder are not good as the slip hangs in the pouring. One of these jugs is filled with slip which is to be poured carefully from one to the other, allowing it to flow gently down the side. This is to break the air bubbles which are nearly always found to be present and the pouring should be repeated until the slip flows smooth and even.

The mold, being thoroughly dry, is tied around with twine, if in parts, and wedged firmly so that it cannot leak. The slip is then carefully poured so as not to touch the sides and the mold is filled until a small mound of slip rises over the edge. This mound will at once begin to sink as the water is drawn into the walls of the mold and slip must be added, little by little, to make good the loss. A small quantity of clay will now be found to have stiffened at the rim of the mold and if this be carefully removed with a steel tool the thickness of the wall of the vase will be seen. If not thick enough the mold must be continually filled up until the necessary thickness is attained. The mold is then carefully lifted, making sure that the bottom is held firmly, and the slip is poured out. It should not be poured back into the casting-jug but into another vessel.

The mold is now set upside down to drain. It should not be placed upon the table but upon two sticks laid parallel so that the drip may hang clear. Several molds may be filled in this way at one time and after about twenty minutes the one first filled may be opened. The bottom is gently detached and the upper part of the mold, consisting of two halves, is laid upon the table on its side. A little gentle manipulation will now suffice to lift the one half and the vase will be seen lying in the other half as in a cradle. The clay is still very soft and must be treated carefully. The half mold, with the contained vase, is taken in the left hand and held nearly upright, the fingers below, the thumb on the top. Now set the fingers of the right hand under the bottom of the vase, rest the thumb lightly against the side and tilt the half mold gently forward. If mold and clay are in good condition the vase will fall forward to be supported on the fingers of the right hand and steadied by the thumb. The half mold is now laid down and the vase taken in both hands, set gently on a plaster bat and put aside to dry. It often happens that the vase leaves the mold with reluctance. If the slip be very new, or the mold either damp or hard or worn out there will be some difficulty in effecting a separation. By allowing the work to stand a while, however, and by slightly jarring the mold from time to time with the ball of the thumb the piece can generally be removed without damage.

In using a new mold it is customary to make what is called a "waste filling." The mold is filled with slip and at once emptied. After standing a few minutes it is forcibly opened and the thin layer of clay inside is picked out with a ball of plastic clay pressed against it. A tool should never be used as this will damage the face of the mold. If the clay should stick obstinately a soft cloth used over the finger will remove it. The reason for this waste filling is that it removes the scum which occurs on all new molds.

Cast ware should not be touched until quite dry and then the spare at the neck is carefully cut off, the seams scraped down and the whole surface smoothed with fine sand paper and a soft cloth. Worn out linen serves excellently for this purpose.

Cups and bowls, if molded, are made without spare at the top. In this case great care must be taken to see that the edge is left clean and smooth in the casting. The spare neck on a vase acts as a margin of safety, as it is completely cut away in the finishing. If a piece has no spare the edge must be left without blemish at the first.