Glass annealing oven

A glass annealing oven provides controlled cooling for a finished hot glass object. Its purpose is to reduce internal stress caused when different parts cool and contract unevenly.

Its role in production

The oven holds glass warm before the temperature is lowered through a suitable cooling cycle. Thickness and glass composition affect that cycle. Distinguish an annealing oven from a melting furnace, which supplies molten glass, and a reheating furnace used during shaping. Slow cooling is a production process, not a guarantee that the object can subsequently withstand every temperature change.

Relevance to collectors

An ordinary photograph or signature does not establish correct annealing. When buying older glass, describe visible cracks, rim chips and repairs individually. Do not attribute a crack to faulty annealing without professional examination, or treat an old glass object in a domestic oven as an assumed repair.

Sources: Corning Museum of Glass: Annealing; Immateriell kulturarv: avspenningsovn i norsk glasshåndverk; Store norske leksikon: avspenning.