Page:The American Cyclopædia (1879) Volume IV.djvu/90

 82 CASTING adding clay. A whole mould may then be taken, and such portions as were added may be removed from the cast by appropriate tools, thus avoiding the use of a piece mould. When the mould is made in parts, it may be done by pouring the plaster over a portion, letting it set, removing it and paring the edge, which is slightly oiled or washed with a mixture of clay and water, replacing it, and adding one or more sections afterward. Another plan, which may be practised with great facility, is to make the mould in one piece and afterward saw it into sections with a very thin, fine saw. If a very fine impression is desired, the mould should be saturated with water, laid upon its back, and, if composed of more than one piece, held in place by supports. A mixture of plas- ter and water, carefully stirred together, is then turned into the mould and over the plane surface, to an extent sufficient to form a base to the cast, of any desired dimensions. If several copies are wanted, and there are no very fine lines to be preserved, the mould may be varnished with shellac and alcohol. Pre- vious to applying the varnish it may be painted with linseed oil, in which case it should first be dried ; but if oil is not used, the varnish may be applied to the green mould with more advan- tage than to allow it to dry. In removing the mould from the cast a good deal of care is re- quired, and successful manipulation is not at- tained without considerable experience. In making a cast of a clay model of a bust, two methods may be pursued. The entire model may be covered over with the plaster mix- ture, by throwing it on in a creamy state with a cup or spoon, and lastly by spreading it on with the hands, until the proper thickness is attained to give sufficient strength; and FIG. 20. Bust covered with Plaster Mould. then, after setting, the mould may be cut into sections with a very thin saw and care- fully removed. (Seq fig. 20.) The process more usually preferred is to apply the plaster in sections by the method of parting. A common way is to make only two sections, the smaller one embracing merely the crown of the head. This plan requires that the frame on which the bust was modelled shall be so constructed that it may be taken apart and re- moved by the hand, after the plaster is well set. After the mould has been carefully clean- ed with water and a soft brush, the parts are put together and bound by a strong cord or rope, and the seams stopped on the external surface with cream of plaster. After this is set the mould is saturated with water. The bust is then cast by turning into the cavity suc- cessive batches of cream of plaster, at the same time turning the mould about in such a man- ner as to cause the plaster to run into all the lines and furrows, and to be deposited in suffi- cient thickness all over the interior surface. In this way a hollow cast is made without the use of a core. After the plaster is well set, the bust may be placed upon a table and the mould FIG. 21. Machine for Casting a Bust. chipped off with a chisel and mallet. This is an operation which requires great care, and can only be done by an experienced hand, and by none so well as by the artist himself. The casting of a bust is rendered much easier by swinging the mould in a pair of strong, con- centric iron rings. (See fig. 21.) This device allows it to be turned with ease in any position, greatly facilitates the operation, and diminish- es the chances of making a defective cast. The plaster bust is used as a model by the marble cutter in reproducing the work of the artist. When several copies in plaster are desired, it is used as a model on which to form a piece mould, which may serve in producing an in- definite number of copies. A statue in plaster may be cast in a variety of ways, depending upon the purpose for which it is intended ; whether to be preserved as a plaster statue, or copied in marble, or to be used as a model from which to make a bronze cast. If it is to be preserved as a statue, it will be cast as nearly as may be in one piece ; but if to be used as a model or pattern by the bronze founder, it