16 CONTEXT 177 : SEPTEMBER 2023 Polished plate glass was manufactured from 1773, providing high quality glass, mostly for use in mirrors, coaches, shopfronts and the homes of the very wealthy. The process was very labour intensive and therefore expensive. Molten glass was cast on to large iron tables, rolled flat, and then placed in an annealing oven to cool. A grinding wheel was used to Manufacturing mechanical cylinders Creating mouthblown cylinders remove roughness and polish the glass to a very smooth finish. In 1789 the British Cast Plate Glass Company began using a steam-powered machine to grind and polish plate glass, a process permitting large panes. The glass was thick and heavy, to bear the large size, and glass tax made it expensive at the time. Improved cylinder glass became available in the early 19th century, following developments in the earlier broad sheet process. Blown cylinders were swung in a trench to achieve sizes of around 4 x 0.6 metres. Larger resulting cylinders were flattened out and cut into sizeable panes which were more affordable and of better quality than crown glass. Improved cylinder glass was used to glaze the Crystal Palace in 1851. Cylinder glass has a slightly rippled surface and long air bubbles align with the ripples to form straight, parallel lines. Machine drawn cylinder glass was produced from 1903, when glass manufacture was developed on an industrial scale in the USA, propelled by advances coal and gas firing technologies. The American Window Glass Company in Pittsburgh, Pennsylvania, developed a method for making very large cylinders 12 metres high. These were mechanically drawn vertically from a circular tank, after which the glass was slowly cooled, cut lengthways, reheated and flattened to form vast sheets of cylinder glass. In the UK machine drawn cylinder glass was manufactured by Pilkington from 1910 to 1933.
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