lagre

A lagre is a large sheet of refractory material, typically cast iron or ceramic, onto which hot glass cylinders are laid during the casting and annealing process in traditional glassmaking. The cylinders, which are formed by the muff process or similar methods, are transferred from the kiln while still plastic and must be cooled in a controlled manner to prevent cracking. The lagre provides a stable, heat-resistant platform for this critical cooling phase.

The material and dimensions of a lagre depend on the glassworks and the size of cylinders being produced. Cast iron lagres are common because they conduct heat evenly and withstand the thermal shock of repeated use. The surface must be sufficiently flat and smooth to support cylinders without distortion, and large enough to accommodate multiple pieces. A lagre may measure several meters in length and width, depending on production scale and the working space available in the annealing lehr.

The lagre works in tandem with the annealing lehr, the oven where cylinders are gradually cooled to relieve internal stress. Cylinders are arranged on the lagre as they enter the lehr mouth, and the lagre itself moves through the lehr on a system of rollers or rails. Temperature control is vital: if cooling happens too quickly, the glass will crack; too slowly, production slows. The lagre's mass and material properties help regulate heat transfer and ensure uniform cooling across all pieces resting on it.

The term lagre derives from older French industrial vocabulary and remains in use primarily in European glassmaking traditions, particularly in sheet glass manufacture. Regional variations exist in construction and naming; some works use the term interchangeably with base plate or kiln furniture. Wear and thermal cycling eventually degrade the lagre surface, requiring resurfacing or replacement. A damaged or warped lagre leads directly to defective glass sheets, making its maintenance a central concern in quality control.