It is likely that you will not have given much thought to how glass is made. In fact, it is very difficult to make flat glass to the standard needed for uses such as shop windows, cars, and mirrors. Or at least it was before Sir Alastair Pilkington (1920-1995) created the float process in 1959 in the United Kingdom. He was a technical engineer at the glass manufacturers Pilkington Brothers (no relation) and it took him seven years to perfect his technique. Before this, the plate process, first developed by English engineer Henry Bessemer in 1848, was used. But this process was expensive because it resulted in distortion and marking of the glass, which had to be corrected by polishing.
In the float process, the melted glass mixture. traditionally made of a combination of silica, sodium carbonate, calcium oxide, magnesium oxide, and aluminum oxide, is poured onto a bath of molten tin. This forms a floating ribbon of glass that is perfectly smooth on both sides and evened out to a uniform thickness of ¼ A inch (6.8 mm)—although thinner glass can be made by stretching this glass ribbon and thicker glass can be made by not allowing the glass pool to flatten. It travels along the tin bath, cooling gradually and then undergoes a heat treatment in a long furnace called a lehr. This is necessary because if the glass cools over quickly, the stress will be too great and it will break under the cutters.
A float glass line can be nearly 1/3 mile (0.5 km) in length and can produce up to 3,728 miles (6,000 km) of glass a year. Thanks to this innovative method, 970,000 tons of flat glass is created every week by around 370 float plants all over the world.
