Process whereby glass, usually flat, is transformed when placed on raised or hollow supports in a kiln, and fired until soft. In contemporary glass production this technique is frequently used in conjunction with other techniques, especially with fusing. When heated, the sheet of glass will bend and stretch to faithfully record the details of the prepared form. The firing temperature is carefully controlled to rise at a specific rate up to 850 - 900° C, then abruptly dropped to 600° C. Slumping consists of heating and softening the sheet of glass over a hollow form. At approximately 700° C gravity begins to pull and reshape the sheet of glass, giving it the precise shape of the mold. These steps are followed by annealing and cooling. Any flat glass can be slumped, but care must be taken to not mix types of glass that are incompatible. As far as molds are concerned, ceramic fibers are currently very popular for their ease in handling and resistance to high temperatures.

Already in ancient times, slumping was known and practiced, particularly for mosaic bowls made from disks placed on hemispherical forms, which when fired and softened would take on the curved shape of their support. In the 1980’s contemporary glass artists adopted this technique in the execution of authentic sculptures using readily available raw materials such as window glass, which lend an unexpected nobility to their otherwise austere works.

Let us cite the pure and fluid compositions of France’s Véronique Monod in the 1990’s, as well as the strange sculptures of the American Mary Shaffer, which combine glass with metal (often tools), and where the transcended technique of slumping must yield to the demands of her powerful and symbolic method.

DE MIRBECK Xavier,”Technique du Verre”, Dessain et Tolra, Paris, 1992