Making Window Glass by the Crown Glass Method — Spinning Molten Glass into Flat Panes

The crown glass method was the dominant technique for making flat window glass from the medieval period through the early 19th century. A glassblower gathers molten soda-lime glass on a blowpipe, blows a hollow sphere, transfers it to a pontil rod, opens the sphere at the blowpipe end, and then spins the open vessel rapidly. Centrifugal force flattens it into a large circular disc called a 'crown' or 'table,' typically 1.0–1.5 metres across. Once annealed and cooled, rectangular panes are cut from the disc. The characteristic bull's-eye at the centre — the pontil mark where the rod was attached — is a hallmark of historic crown glass windows.