Polished plate
Encyclopedia
Polished plate is a type of hand-blown 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 of producing hand-blown window glass included: broad sheet
, blown plate
, crown glass
and cylinder blown sheet
. These methods of manufacture 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, machine drawn cylinder sheet
, flat drawn sheet, single and twin ground polished plate and float glass
.
The Frenchman, Louis Lucas de Nehou, in 1688, in conjunction with A. Thevart, succeeded in perfecting the process of casting plate-glass. Mirror plates previous to the invention had been made from blown "sheet" glass, and were consequently very limited in size. De Nehou's process of rolling molten glass poured on an iron table rendered the manufacture of very large plates possible.
In 1773 English polished plate (by the French process) was produced at Ravenhead
.
By 1800 a steam engine was used to carry out the grinding and polishing of the cast glass.
Glass
Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...
. 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 of producing hand-blown window glass included: broad sheet
Broad sheet
Broad sheet is a type of hand-blown glass. It is made by blowing molten glass into an elongated balloon shape with a blowpipe. Then, while the glass is still hot, the ends are cut off and the resulting cylinder is split with shears and flattened on an iron plate. . The quality of broad sheet...
, blown plate
Blown plate
Blown plate is one of many types of hand-blown glass. It is made from broad sheet glass by laboriously hand grinding and polishing both surfaces. Blown plate is of a sufficient quality and size for mirrors and coach glasses....
, crown glass
Crown glass (window)
Crown glass was an early type of window glass. In this process, glass was blown into a "crown" or hollow globe. This was then transferred from the blowpipe to a pontil and then flattened by reheating and spinning out the bowl-shaped piece of glass into a flat disk by centrifugal force, up to 5 or...
and cylinder blown sheet
Cylinder blown sheet
Cylinder blown sheet is a type of hand-blown window glass. It is created with a similar process to broad sheet, but larger cylinders are produced by swinging the cylinder in a trench. The glass is then allowed to cool before the cylinder is cut. The glass is then re-heated and flattened...
. These methods of manufacture 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, machine drawn cylinder sheet
Machine drawn cylinder sheet
Machine drawn cylinder sheet was the first mechanical method for "drawing" window glass. Cylinders of glass 40 feet high are drawn vertically from a circular tank. The glass is then annealed and cut into 7 to 10 foot cylinders. These are cut lengthways, reheated, and flattened.This process...
, flat drawn sheet, single and twin ground polished plate and float glass
Float glass
Float glass is a sheet of glass 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...
.
The Frenchman, Louis Lucas de Nehou, in 1688, in conjunction with A. Thevart, succeeded in perfecting the process of casting plate-glass. Mirror plates previous to the invention had been made from blown "sheet" glass, and were consequently very limited in size. De Nehou's process of rolling molten glass poured on an iron table rendered the manufacture of very large plates possible.
In 1773 English polished plate (by the French process) was produced at Ravenhead
Ravenhead
Ravenhead is an area of St Helens in the North West of England. It is bordered by Thatto Heath, Sutton Heath, Eccleston and the Town Centre. The area is thought to take its name from a farm once located nearby , while the 'head' portion of the name represents its location at one of the higher...
.
By 1800 a steam engine was used to carry out the grinding and polishing of the cast glass.