技法
Air Vent Groove
Japanese: 空気抜き溝
A groove approximately 2 mm wide on the back of a sagging mold. This is a structural element of the mold designed to allow air between the mold and the glass to escape, ensuring that the glass settles evenly into the mold cavity.
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An air vent groove is an exhaust structure provided on the back surface of a perforated mold used in shallow sagging; it is machined as a V-shaped groove approximately 2 mm wide (Treatise §9.2, Chikaoka 2021, pp. 21–23, p. 32). During sagging firing, when the perforated mold is placed on a shelf and the glass sinks into the holes in the mold, air becomes trapped in the space between the shelf and the mold. This trapped air acts as an “air spring,” causing problems such as uneven deformation of the glass or hindering its deformation. This problem is solved by using grooves on the back of the mold to allow the trapped air to escape from the mold.
As a practical note, while the grooves on the back of the mold do not affect the mold’s surface (molding surface) that comes into contact with the glass, it is important that the grooves extend all the way to the edge of the mold. If the grooves are closed off, air cannot escape. The grooves can be straight or diagonal; they are often arranged radially or in a grid pattern extending from the central hole toward the rim of the mold. For homemade fire-resistant plaster molds (chikaoka-plaster), the grooves are cut and shaped using a metalworking chisel or carving knife after the mold has hardened and dried. In commercially available bisque-fired ceramic molds, this grooving is often omitted; in such cases, an alternative method is to insert a thin spacer between the mold and the shelf to allow air to escape from the edge of the mold.
Related Concepts
Sagging, Slumping, Chikaoka-style Refractory Plaster, Refractory Plaster, Plate-Sag Formula
This entry is written in Japanese by Rei Chikaoka and translated for readers outside Japan. If something reads oddly, the original is the source of truth.