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Molds For Glass
Making patterns in glass by means of molds is an old and popular method. This is accomplished by either blowing, pressing or pouring the hot metal into the mold. As soon as the blowing iron was invented, glass was blown into clay molds which not only shaped the object but gave it a pattern. In the nineteenth century, clay was still used, but molds made of hard woods, brass, copper, and iron soon displaced clay.
The earliest molds were made in one piece which meant the top of the mold must be its widest part. These "dip" or "open top" molds were also used extensively to impress a gather of glass. Instead of finishing the piece to the size of the mold, it was expanded into a larger article as in pattern-molding. Full-size piece molds, often called "open and shut," are made of two or more parts hinged together. This allows an article of uneven dimensions to be shaped entirely in a mold. At first even these did not finish the piece; rims, handles, collars, feet, and necks had to be done by hand. During the nineteenth century, molds were improved. New ways of molding whole articles were invented. By the latter part of the century even the defects caused in the glass by contact with the metal were somewhat removed by chilling the iron molds. With the introduction of automatic machines, molds and moldmaking were further improved. However, the making of molds has always been a costly part of the process and has required skilled workers.
Molds are filled in three ways. The glass is gathered on the blowing iron and blown into the mold until it contacts the inner surface. This requires skill and practice on the part of the glassblower. If it is a piece mold, an apprentice usually operates the handles. For hand-pressed glass, the hot glass is gathered on a rod, cut off with shears, and allowed to drop into the mold. For machine-blown or pressed ware, the hot glass is automatically poured into the mold.
The most significant contributions that American glassworkers have made to glassmaking is in the field of mass production of automatic machinery for tableware, laboratory, industrial, and architectural glass.
Most collectors of glass are interested in knowing how their treasures were made. The best way to understand the intricate art of fabricating glassware is to see it done. However, few collectors have the opportunity of seeing many types of blown and pressed glass made and decorated. Reading about the processes and then studying each piece will familiarize the collector with the art of glassmaking. It will also help you to choose authentic glass for your collection.