Polished plate is a next type of hand-made glass. It is produced by casting glass onto a table and then subsequently grinding and polishing the glass. This was originally done by hand, and then later by machine. It was an expensive process requiring a large capital investment. Other methods for making hand-blown glass included blown plate glass, crown glass, polished plate glass and cylinder blown sheet glass lasted at least until the end of the 19th Century. The early 20th century marks the move away from hand-blown to machine manufactured glass such as rolled plate glass, machine drawn cylinder sheet glass, flat drawn sheet glass, single and twin ground polished plate glass and finally float glass. A modern way of window glass producing is a Float glass method. The sheet of glass is made by floating molten glass on a bed of molten metal, typically tin, although lead and various low melting point alloys were used in the past. This method gives the sheet uniform thickness and very flat surfaces. Modern windows are made from float glass. Most float glass is soda-lime glass, but relatively minor quantities of specialty borosilicate and flat panel display glass are also produced using the float glass process.The float glass process is also known as the Pilkington process, named after the British glass manufacturer Pilkington, which pioneered the technique (invented by Sir Alastair Pilkington) in the 1950s.