Crown glass was one of the two most commonly used types of glass for windows up until the 19th century, the other being blown plate glass. The process of making crown glass was first perfected by French glassmakers in the 1320s. Crown glass is made without lead, chiefly by fusing fixed alkali with silica sand, to which is added some black oxide of manganese – which gives the glass a tinge of purple.
The finished “table” of glass was thin, lustrous, highly polished (by “fire-polish”), and had concentric ripple lines, the result of spinning; crown glass was slightly convex, and in the centre of the crown was the bull’s eye - a thickened part where the pontil was attached. This was often cut out as a defect, but later it came to be prized as evidence of antiquity. Nevertheless, and despite the availability of cheaper cylinder glass (cast and rolled glass had been invented in the 17th century), crown glass was particularly popular for its superior quality and clarity.
This process allows the colour range to be limitless; crown glass is used ecclesiastically, commercially, domestically and for restoration purposes.
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