Slumping (kiln shaping of glass)

Slumping reheats a glass blank until it softens and takes the shape of a mould beneath or around it under its own weight. The term sagging is also used. Applications include bowls and platters.

Shaping and joining are different stages

Fusing joins glass components through heat. Slumping changes the blank's shape. A decorated fused blank can therefore be shaped into a platter in a subsequent firing. The terms describe different stages, not necessarily different objects.

The mould, material and intended result affect the firing process. Bullseye states that there is no single slumping temperature suitable for every project. A particular temperature should therefore not be used to identify an unknown work conclusively.

Assessing an object

Photograph the profile, underside, edges and decoration. Record dimensions, cracks, chips and any repairs in a condition report. A bowl shape alone does not establish process, maker or age. Retain signatures, labels and receipts that may support identification.

Explore available works in glass and crystal. For an object you own, clarify the purpose of a valuation before requesting one.