Broad sheet is a type of hand-blown 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 made by blowing

Glassblowing

Glassblowing is a glassforming technique that involves inflating molten glass into a bubble, or parison, with the aid of a blowpipe, or blow tube...

 molten glass into an elongated balloon shape with a blowpipe

Blowpipe (tool)

The term blowpipe refers to one of several tools used to direct streams of gases into any of several working media.- Blowpipes for torches :...

. 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. (This is the forerunner of the cylinder process

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...

). The quality of broad sheet glass is not good, with many imperfections. Due to the relatively small sizes blown, broad sheet was typically made into leadlight

Leadlight

Leadlights or leaded lights are decorative windows made of small sections of glass supported in lead cames. The technique of creating windows using glass and lead came is discussed at lead came and copper foil glasswork...

s.

Other methods for making hand-blown glass included blown plate glass, 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...

, polished plate glass and cylinder blown sheet glass. 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 glass, machine drawn cylinder sheet glass, flat drawn sheet glass, single and twin ground polished plate glass 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...

.

According to the website of the London Crown Glass Company, broad sheet glass was first made in the UK in Sussex

Sussex

Sussex , from the Old English Sūþsēaxe , is an historic county in South East England corresponding roughly in area to the ancient Kingdom of Sussex. It is bounded on the north by Surrey, east by Kent, south by the English Channel, and west by Hampshire, and is divided for local government into West...

in 1226 CE. This glass was of poor quality and fairly opaque. Manufacture slowly decreased and ceased by the early 16th Century. French glassmakers and others were making broad sheet glass earlier than this.

Sources