Float glass is so called because the molten liquid is allowed to flow over and float on a layer of molten tin. It can then form a perfectly smooth and glossy surface of even thickness. The glass is allowed to cool and solidify in a controlled manner. This annealing process means there is no cracking or straining and the resultant product is less brittle.
The process was devised by Alastair Pilkington in the 1950s. Previously glass was made by drawing liquid from a furnace to form window glass. This was a cheap method but the quality of the glazing was inferior in quality and appearance. It was only suitable for use in situations where some distortion was acceptable. Higher quality plate glass was produced by laying molten liquid to solidify on a bed of iron to form sheets which were then ground and polished.
Today 90% of glass is produced using the float method.