Rev. 2003-02-06, -02-27, 2005-11-21
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Oh, boy, is this an area in which I am not an expert. The purpose of this page is to have some pointers to better information for those who are interested.
Glass may be cast by pouring it molten into a heated mold or by putting cold glass in a holder above a mold and raising both to glass flow temperatures (kiln casting) or by packing broken glass (frit) into a mold and raising both to fusing temperature, which preserves the placement of the (often colored) glass but leaves air bubbles in the glass for a translucent rather than clear result.
Glass is cast in any of the materials used for casting metal (sand, silica molds, iron, etc.) the most common one being 50% silica flour with plaster of Paris which makes a fairly cheap, but weak and normally not reusable mold. When heated, the mold is pretty weak so it is usable in kiln casting but not with application of force.
Within the art glass community, one form of casting glass seems rarely discussed, although it is extremely common throughout glass history and thousands of pieces per day are produced in the commercial glass market. Perhaps because of the common usage and perhaps because of the technical complications, pressed glass is not commonly discussed with casting glass, and it will not be here, but there.
Solid casting often involves long annealing times because the annealing must be based on the thickness of the piece plus the thickness of the mold. If the glass plus the mold is 4 inches or more thick, the annealing time goes up into days and weeks.
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