In earlier centuries, window glass or flat glass was made by blowing either large cylinders or large disks. The cylinders were cut apart and flattened and then window panes were cut from the large surface. Most glass for windows up to the early 19th century was made from rondels, while most window glass during the 19th century was made using the cylinder method (these 'cylinders' were 6 to 8 feet (2 to 2.5 m) long and 10 to 14 inches (250 to 350 mm) in diameter).
The flat glass process was patented in 1848 by Henry Bessemer, an English engineer was the first attempt to make a continuous ribbon of flat glass by forming the ribbon between rollers. The forming of flat glass on a tin bath was described in patents in the United States in 1902 by W. E. Heal and again in 1925 by Hitchcock (a revised version of Heal's patent). Between 1953 and 1957, (Sir) Alastair Pilkington and Kenneth Bickerstaff of the UK's Pilkington Brothers developed the first successful commercial implementation of the forming of a flat glass continuous ribbon glass using a molten tin bath on which the molten glass flows laterally unhindered to the limit of its free flow under the influence of gravity and surface tension. Neither Heal nor Hitchcock had described this free flow process. Full scale profitable sales of float glass were first achieved in 1960.
Before the development of float glass, larger sheets of plate glass were made by casting a large puddle of glass on an iron surface, and then grinding and polishing both sides to smooth clarity, a very expensive process. From the early 1920s, a continuous ribbon of plate glass was passed through a lengthy and expensive series of inline grinders and polishers, helping to reduce glass losses and production costs.
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