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In the production of flat glass (where, as explained earlier, molten glass had previously been poured onto large tables then rolled flat into “plates”, cooled, ground and polished before being turned over and given the same treatment on the other surface), the first real innovation came in 1905 when a Belgian named Fourcault managed to vertically draw a continuous sheet of glass of a consistent width from the tank. Commercial production of sheet glass using the Fourcault process eventually got under way in 1914.

The Fourcault process requires a “pit” or drawing area and an assembly of machines to draw up the ribbon of glass while performing actions upon it that ensure desired quality and process yields. Today most glass manufacture has a “hot end” where the products are made. Fourcault is no exception.

The action in Fourcault happens “at the draw”, or area where the glass is taken from a liquid state into the start of the process needed to make it into flat glass.

At the bottom of the draw is the “pit” or place where the molten glass is sufficiently cooled to be close to forming temperature. The cooling process uses a device known as a “canal”. As the name describes a Canal is a box shaped structure which conveys the glass from the refining area to the pit.

The canal links the pit with the “refining” area, a section of the glass furnace that removes gas bubbles and other sources of imperfection. Since refining requires much higher temperatures to release gas bubbles than those required to form the glass it is not possible to draw directly from the refining area, hence the need for canals.

Around the end of the First World War, another Belgian engineer Emil Bicheroux developed a process whereby the molten glass was poured from a pot directly through two rollers. Like the Fourcault method, this resulted in glass with a more even thickness, and made grinding and polishing easier and more economical.

An off-shoot of evolution in flat glass production was the strengthening of glass by means of lamination (inserting a celluloid material layer between two sheets of glass). The process was invented and developed by the French scientist Edouard Benedictus, who patented his new safety glass under the name “Triplex” in 1910.

In America, Colburn developed another method for drawing sheet glass. The process was further improved with the support of the US firm Libbey-Owens and was first used for commercial production in 1917. The glass ribbon is drawn vertically from the tank for about 70 cm by a metal “bait” before being bent over a roller into the horizontal plane ready for cutting and annealing. The drawing speed with the Libbey-Owens process is twice that of the Fourcault process.

The Pittsburgh process, developed by the American Pennvernon and the Pittsburgh Plate Glass Company (PPG), combined and enhanced the main features of the Fourcault and Libbey-Owens processes, and has been in use since 1928. The glass is drawn from the melt and conveyed vertically through an annealing shaft around 12 metres long prior to cutting.

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