Metal Sculpture: Polystyrene Patterns in Ceramic Shell Molds

Leotzurcio, Vol. 10, pp. 34-36. Pergamon Press 1977. Printed in Gret Britain. METAL SCULPTURE: POLYSTYRENE PATTERNS IN CERAMIC SHELL MOLDS Richard Davis* 1. Sculptors and craftsmen have been fascinated for thousands of years with the possibilities and the enduring qualities of castable metals such as bronze and so am 1. Since my earliest experiences with art, I have maintained an interest in the process of metal casting as a way of producing art objects. The two main concerns of a craftsman working with the process are the type of pattern and the kind of mold to be selected. For lack of a better material, patterns have been made of wax for at least 3000 years. The material for molds, however, has varied considerably, since sculptors relentlessly search for a better refractory material. The purpose of this report is to present the results of my experiences in using a plastic for patterns and a ceramic shell for molds. Ceramic shell, a relatively new type of mold-making material, provides significant advantages to sculptors. Compared with other types of investment molds, the ceramic shell mold is superior for producing small details and for its reliability in casting relatively small objects. On the other hand, the initial financial outlay for equipment and the need to give special attention to certain steps of the technique are much greater than for solid investment molds. After I had tried using many types of molds, I decided that ceramic shell molds are the most suitable for my purposes and 1have used them exclusively during the past five years. Having made this decision, I turned to the problem of materials for patterns, which still concerns me. Incidentally, the process for constructing ceramic shell molds, which involves the application of several layers of silica (sand) with a liquid binder to a pattern, is described in Ref. I . 2. Ever since the lost-wax process was introduced, it has been accepted as the best way to cast complex positive forms [2,3]. In some cases, other materials, such as Styrofoam, have been substituted for wax and have been removed from the resulting mold by means of a solvent or by melting and decomposition [4-71. In most cases, however, wax has predominated as a pattern material because of its adaptability to the needs of most sculptors who cast metal. Even with the advent of ceramic shell, wax as a pattern material has continued to be the one that performs most satisfactorily. Nevertheless , I do not like working with wax and I feel that I am unable to obtain with it the forms that I desire. Furthermore , I believe that other sculptors share my feelings, *Sculptor and teacher. Dept. of Art, North Texas State University, Denton, TX 76203, U.S.A. (Received 9 June 1975.) particularly those whose cast-metal sculpture is of a non-traditional kind. In my search for other pattern materials, I was attracted by the advantages over wax possessed by some plastics (the thermoplastic kind). For example, they can be molded, filed, sawed, welded, machined, sanded, planed, bent and vacuum-formed. However, like wax, the plastics that may be used in this application, possess the disadvantage of expanding inside a mold while being heated risking breakage of the mold before the pattern starts melting and flowing off. 1 am aware that plastic has been used as a pattern material for making very small ceramic shell molds (e.g. for finger rings) [8]. In this case, when the pattern is very small, the plastic can sometimes be burned out without breaking the mold. But with larger patterns the chance of breakage is greater and I am unaware of any attempts by others to use plastic patterns in this way. 3. The problem of expansion of wax patterns is overcome by 'shock-heating' the mold and pattern [I]. The mold containing a pattern is put into a very hot oven, over 1500°C (I prefer a temperature close to 2000°C). The sudden heating of the outer layer of the wax pattern causes it to melt and flow away before the main bulk of the pattern becomes warm and begins to expand. The space left by the removed...