Crown glass (window)

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Crown glass

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 punty and then flattened by reheating and spinning out the bowl-shaped piece of glass (bullion) into a flat disk by centrifugal force, up to 5 or 6 feet (1.5 to 1.8 metres) in diameter. The glass was then cut to the size required. [1]

The thinnest glass was in a band at the edge of the disk, with the glass becoming thicker and more opaque toward the center. Known as a bullseye, the thicker center area around the pontil mark was used for less expensive windows. To fill large window spaces with the best glass, many small diamond shapes were cut from the edge of the disk, and then some might be halved into triangles. These were mounted in a lead lattice work and fitted into the window frame.

Crown glass was one of the two most common processes for making window glass until the 19th century. The other was blown plate. Crown glass window panes with ceramic frames have been found at Soba East, the medieval capital of Alodia. They are only 110–115 millimetres (4.3–4.5 in) in diameter and were probably used to provide light in storerooms. [2] The process of making crown glass window panes was perfected by French glassmakers in the 1320s, notably around Rouen, and was a trade secret. Hence crown glass was not made in London until 1678.

Crown glass is one of many types of hand-blown glass. Other methods include: broad sheet, blown plate, polished plate 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. [3]

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Glassblowing Technique for forming glass

Glassblowing is a glassforming technique that involves inflating molten glass into a bubble with the aid of a blowpipe. A person who blows glass is called a glassblower, glassmith, or gaffer. A lampworker manipulates glass with the use of a torch on a smaller scale, such as in producing precision laboratory glassware out of borosilicate 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 other various low-melting-point alloys were used in the past. This method gives the sheet uniform thickness and very flat surfaces.

Cathedral glass

Cathedral glass is the name given commercially to monochromatic sheet glass. It is thin by comparison with slab glass, may be coloured, and is textured on one side.

Glass tubes are mainly cylindrical hollow-wares. Their special shape combined with the huge variety of glass types, allows the use of glass tubing in many applications. For example, laboratory glassware, lighting applications, solar thermal systems and pharmaceutical packaging to name the largest.

Lapping

Lapping is a machining process in which two surfaces are rubbed together with an abrasive between them, by hand movement or using a machine.

Blown plate is a hand-blown glass. There is a record of blown plate being produced in London in 1620.

Broad sheet glass

Broad sheet is a type of hand-blown glass. It was first made in Sussex in 1226.

Polished plate is a 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.

Cylinder blown sheet is a type of hand-blown window glass. It is created with a similar process to broad sheet, but with the use of larger cylinders. In this manufacturing process glass is blown into a cylindrical iron mold. The ends are cut off and a cut is made down the side of the cylinder. The cut cylinder is then placed in an oven where the cylinder unrolls into a flat glass sheet. William J. Blenko used this method in the early 1900s to make stained glass. The result is much larger panes and improved surface quality over broad sheet, although still containing some imperfections. These imperfect panes have led to the misconception that glass is actually a high-viscosity fluid at room temperature, which is not the case.

Machine drawn cylinder sheet was the first mechanical method for "drawing" window glass. Cylinders of glass 40 feet (12 m) 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.

Rolling (metalworking) Metal forming process

In metalworking, rolling is a metal forming process in which metal stock is passed through one or more pairs of rolls to reduce the thickness, to make the thickness uniform, and/or to impart a desired mechanical property. The concept is similar to the rolling of dough. Rolling is classified according to the temperature of the metal rolled. If the temperature of the metal is above its recrystallization temperature, then the process is known as hot rolling. If the temperature of the metal is below its recrystallization temperature, the process is known as cold rolling. In terms of usage, hot rolling processes more tonnage than any other manufacturing process, and cold rolling processes the most tonnage out of all cold working processes. Roll stands holding pairs of rolls are grouped together into rolling mills that can quickly process metal, typically steel, into products such as structural steel, bar stock, and rails. Most steel mills have rolling mill divisions that convert the semi-finished casting products into finished products.

Architectural glass

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Leadlight

Leadlights, leaded lights or leaded windows are decorative windows made of small sections of glass supported in lead cames. The technique of creating windows using glass and lead came known as came glasswork. The term leadlight could be used to describe all windows in which the glass is supported by lead, but traditionally, a distinction is made between stained glass windows and leadlights, the former being associated with the ornate painted images on windows of churches and other such works of architecture and the latter with the windows of vernacular commercial and domestic architecture and defined by its simplicity.

A glass cutter is a tool used to make a shallow score in one surface of a piece of glass that is to be broken in two pieces, for example to fit a window. The scoring makes a split in the surface of the glass which encourages the glass to break along the score. This is not to be confused with the tools used to make cut glass objects.

Plate glass

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Medieval stained glass Coloured and painted glass of medieval Europe

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History of glass

The history of glass-making dates back to at least 3,600 years ago in Mesopotamia. However, some writers claim that they may have been producing copies of glass objects from Egypt. Other archaeological evidence suggests that the first true glass was made in coastal north Syria, Mesopotamia or Egypt. The earliest known glass objects, of the mid 2,000 BCE, were beads, perhaps initially created as the accidental by-products of metal-working (slags) or during the production of faience, a pre-glass vitreous material made by a process similar to glazing. Glass products remained a luxury until the disasters that overtook the late Bronze Age civilizations seemingly brought glass-making to a halt.

Vauxhall glassworks was a plate glass factory off what is now the Albert Embankment in the Vauxhall area of Lambeth, London, just to the north of Vauxhall Gardens. The site is now commemorated in the name of Glasshouse Walk.

Solarized architectural glass

Solarized architectural glass is a type of architectural glass, used as a building material, that has changed color as a result of a chemical reaction between a glass decolorizer and ultra-violet light. Sometimes known as "desert glass", or "sun-purpled glass", solarized glass is most commonly observed as bottles and glassware. However, solarized glass does occasionally appear in architectural contexts and uses, especially window panes, doorknobs, and pavement lights. The physical characteristics and the relative rarity of this glass for windows has meant that it is understood as a distinct glass type.

References

  1. "The Glassblowing Process". Sugar Hollow Glass. Retrieved June 15, 2009.
  2. D. Welsby (1992), "Windows in Medieval Nubia: The Evidence from Soba East", The Antiquaries Journal, 72, 174–178. doi : 10.1017/s0003581500071250
  3. "Hand-blown glass: manufacturing process". London Crown Glass Company. Retrieved May 25, 2016.