温度・粘度
creep
Japanese: 自重クリープ
A gradual deformation caused by its own weight. The main body of the slump and sagging.
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Creep is a phenomenon in which glass slowly deforms at high temperatures due to its own weight or external forces. Although glass appears to be a solid, it behaves as a viscous fluid at high temperatures, and deformation accumulates over time under a constant stress. Slumping and sagging can be considered forming techniques that make use of intentional creep.
Unintended creep becomes a problem during long firing times or when pieces are refired multiple times. In particular, flat pieces may deform—such as by bending slightly under their own weight or sagging at the edges. To minimize creep, it is important to avoid firing at unnecessarily high temperatures or for excessively long periods, and to place pieces evenly on a flat shelf.
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.