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 Glassblowing is a glassforming technique that involves inflating molten glass into a bubble (or parison) with the aid of a blowpipe (or blow tube). A person who blows glass is called a ''glassblower'', ''glassmith'', or ''gaffer''. A '' lampworke ...

and then flattened by reheating and spinning out the bowl-shaped piece of glass (bullion) into a flat disk by

centrifugal force In Newtonian mechanics, the centrifugal force is an inertial force (also called a "fictitious" or "pseudo" force) that appears to act on all objects when viewed in a rotating frame of reference. It is directed away from an axis which is paralle ...

, up to 5 or 6 feet (1.5 to 1.8 metres) in diameter. The glass was then cut to the size required. 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 A pontil mark or punt mark is the scar where the pontil, punty or punt was broken from a work of blown glass. The presence of such a scar indicates that a glass bottle or bowl was blown freehand, while the absence of a punt mark suggests either th ...

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 Blown plate is a hand-blown glass. There is a record of blown plate being produced in London in 1620. Production Blown plate was made by hand-grinding broad sheet glass. As the process was labour-intensive, and expensive, blown plate was mainly use ...

. Crown glass window panes with ceramic frames have been found at Soba East, the medieval capital of

Alodia Alodia, also known as Alwa ( grc-gre, Aρουα, ''Aroua''; ar, علوة, ''ʿAlwa''), was a medieval kingdom in what is now central and southern Sudan. Its capital was the city of Soba, located near modern-day Khartoum at the confluence of t ...

. They are only in diameter and were probably used to provide light in storerooms. The process of making crown glass window panes was perfected by French glassmakers in the 1320s, notably around

Rouen Rouen (, ; or ) is a city on the River Seine in northern France. It is the prefecture of the Regions of France, region of Normandy (administrative region), Normandy and the Departments of France, department of Seine-Maritime. Formerly one of ...

, 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 Broad sheet is a type of hand-blown glass. It was first made in Sussex in 1226. Production It is made by blowing molten glass into an elongated tube shape with a blowpipe. Then, while the glass is still hot, the ends are cut off and the resu ...

polished plate 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 la ...

and

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 with the use of larger cylinders. In this manufacturing process glass is blown into a cylindrical iron mold. The ends are cut off an ...

. 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 Rolling is a type of motion that combines rotation (commonly, of an axially symmetric object) and translation of that object with respect to a surface (either one or the other moves), such that, if ideal conditions exist, the two are in contact ...

machine drawn cylinder sheet 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 (2 to 3 ...

flat drawn sheet Flat or flats may refer to: Architecture * Flat (housing), an apartment in the United Kingdom, Ireland, Australia and other Commonwealth countries Arts and entertainment * Flat (music), a symbol () which denotes a lower pitch * Flat (soldier), a ...

single and twin ground polished plate Single may refer to: Arts, entertainment, and media * Single (music), a song release Songs * "Single" (Natasha Bedingfield song), 2004 * "Single" (New Kids on the Block and Ne-Yo song), 2008 * "Single" (William Wei song), 2016 * "Single", by ...

and float glass.

References

External links

{{Glass forming Glass production Glass types History of glass