Mold, Molding. The matrix containing the cavities to form a cast piece, and the process of producing that piece. The material to form the casting must be molten, the mold must be capable of sustaining heat and holding the form until the molten material solidifies. There are several kinds of molds, they differ in what they are made of and what they produce. Also molds can be used for only a single cast, these differ from production run casting, where a permanent mold is made often of two or more metal parts for repeated use. The use of molds for medallic production is rather limited, many types of molds have little concern to this field.Types of molds. Molds can be made of a variety of material – called the investment – these can be metal, ceramic, rubber, plaster, epoxy, gelatin, silicone, and, or other. Since numismatic items are concerned with sharp, fine, minute detail, several of these investments, like sand, are not suitable for casting of numismatic or medallic items.Lost wax, (cire-perdue) is a waste wax or waste mold type and is suitable for medallic castings. flexible mold, made of gelatin, rubber or silicon are suitable for casts with undercuts; ideal for medallic plaques. Others – like piece mold – which are used for sculpture in the round – have no application in the numismatic field.The pattern from which the mold is made can be a variety of materials. Often it is wax, plaster, or wood. Some wood patterns for coins were made in Germany in the 15th century. England made coin patterns of iron, these were cast for use on early die-cutting pantographs (which more typically would use an electroform copper pattern.)Molds were used for the cash coins of China for centuries. These formed cash “trees” with sprues still intact from which coins were broken off. Several of these molds still exist in museums today.See also foundry cast.
excerpted with permission from
For Artists, Makers, Collectors and Curators
COMPILED AND WRITTEN BY D. WAYNE JOHNSON
Roger W. Burdette, Editor