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Broadsheet glass

Please read the history of window glass in Britain:

In Britain the first form of glass used for window glazing was known as broadsheet glass, developed originally in Roman times. Around the beginning of the 13th century broadsheet was starting to be made in Sussex by elongating a balloon of blown glass, cutting both ends off and flattening the resulting cylinder on an iron plate.

The end product was at best translucent, of very poor quality and due to the small size of the sheets was made into leaded lights.

This form of window glass was used for at least two centuries however its use declined considerably and by the early 14th century a new product known as crown glass was being imported from France along with French broadsheet.

The imported French crown glass was however very costly which made it affordable only to wealthy property owners.

Crown and plate glass

In the early 17th century blown plate glass was being produced in London using a method of laboriously grinding broadsheet glass, which by now could be produced in larger pieces. Blown plate glass was costly to produce and was used mainly for mirror production and in carriage windows rather than windows in buildings.

Later that century the manufacture of crown glass was started in London made by blowing a sphere of molten glass and spinning it out into a circular sheet. The quality of this glass was much better than that of broadsheet however the size of panes that could be successfully cut were still quite limited which resulted in windows being constructed with many smaller panes.

The central pane cut from these "bullions" contained the bulls-eye, the thickened area where the glass was attached to the "punty", the rod used to spin it.

In the late 18th century the manufacture of polished plate glass was introduced into Britain. The process consisted of casting a sheet of glass onto a table and then grinding and polishing it by hand, superseded at the beginning of the 19th century by steam powered machine-grinding and polishing.

Large panes of very good quality glass could be produced, but it was a very expensive process, so this was generally only used for the windows of the best rooms in larger houses.

Cylinder glass and rolled plate

In 1834 an improved cylinder sheet process was introduced from Germany. This was similar to the process for making broadsheet glass, but technological advances meant that much larger sheets of good quality glass could be produced.

The withdrawal of duty on glass in 1845 led to a great increase in demand as the price dropped by 75% and this method became the main means of manufacturing window glass until the early years of the 20th century.

In 1847 James Hartley introduced a rolled plate obscure glass with a ribbed pattern and in 1888 Chance Bros started to produce machine rolled obscure glass with a variety of patterns.

Laminated and tempered glass

Around the turn of the nineteenth century, laminated glass was developed by means of incorporating a thin plastic film between two sheets of glass which greatly increased the safety and security of much larger windows, which could now be glazed without the need for divisional glazing bars.

In the meantime, Pilkington’s started to produce a wired cast glass followed by the production of their twin ground polished plate glass in 1938.

During the 20th century new continuous mass-production techniques continued to develop leading to cheaper ways to produce a more consistently high-quality glass in larger and larger sheet sizes. Tempered or toughened glass was also developed around this time using a method of quenching heated glass in a bath of oil, this process creates an extremely hard and resilient glass product.

Modern float glass

It was in 1957 however that Sir Alistair Pilkington invented and developed a ground-breaking glass manufacturing system known as 'Float Glass', which is a process still used to this day where molten glass is allowed to float on a bed of molten tin while the upper surface is polished using pressurised nitrogen.

Double and triple glazed units

In the late 20th century as part of the drive to reduce fuel bills by improving the energy efficiency of windows the double-glazing sealed unit was developed, in which moisture absorbent spacers are sealed between two panes of glass leaving an insulating air-space.

Further reductions in the transmission of heat and noise through these units have been achieved by filling the space with argon, by the use of special coatings or films to reflect infra-red radiation and in the introduction of a third layer of glass known as triple glazing.

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