n.
- A soda-lime optical glass that is exceptionally hard and clear, with low refraction and low dispersion.
- A form of window glass made by whirling a glass bubble to make a flat circular disk with a lump left in the center by the glass blower's rod.
crown glass
| Dictionary: crown glass |
n.
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| Architecture: crown glass |
A handmade glass of soda-lime composition, used for windows; manufactured in the early 19th century by a now-obsolete process in which a hollow sphere of glass was blown while still very soft, then spun to form a large, nearly flat circular disk. During the spinning process, ripple lines were formed in a pattern of concentric circles, with their center at the center of the spun disk; this central area was used in a bull’s eye window. Also see glass.
| Archaeology Dictionary: crown glass |
[Ma]
The main method of making sheets of glass in the 18th century ad was to fix a ball of semi-molten glass to the end of a rod and spin it into a disc up to 1.5m across. This left the characteristic thickened ring where the disc was broken from the rod.
| Science Q&A: What is crown glass? |
In the early 1800s, window glass was called crown glass. It was made by blowing a bubble, then spinning it until flat. This left a sheet of glass with a bump, or crown, in the center. This blowing method of window-pane making required great skill and was very costly. Still, the finished crown glass produced a distortion through which everything looked curiously wavy, and the glass itself was also faulty and uneven. By the end of the nineteenth century, flat glass was mass-produced and was a common material. The cylinder method replaced the old method, and used compressed air to produce glass that could be slit lengthwise, reheated, and allowed to flatten on an iron table under its own weight. New furnaces and better polishing machines made the production of plate-glass a real industry. Today, almost all flat glass is produced by a float-glass process, which reheats the newly formed ribbon of glass and allows it to cool without touching a solid surface. This produces inexpensive glass that is flat and free from distortion.
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| Wikipedia: Crown glass (window) |
This article is about the window glass. For the optical glass, see Crown glass (optics).
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 (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.
Due to the distribution of the best glass, in order to fill large window spaces many small diamond shapes would be cut from the edge of the disk and these would be mounted into a lead lattice work and fitted in the window. Known as a bullseye, the thicker center area around the pontil mark was used for less expensive windows.
Crown glass was one of the two most common processes for making glass for windows up until the 19th century. The other was blown plate. The process was first perfected by French glassmakers in the 1320s, notably around Rouen. The process was kept a careful trade secret. As a result, 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.[2]
References
- ^ "The Glassblowing Process". Sugar Hollow Glass. http://www.sugarhollowglass.com/process.html. Retrieved June 15, 2009.
- ^ "Hand-blown glass: manufacturing process". London Crown Glass Company. http://www.londoncrownglass.co.uk/Manufacturing.html. Retrieved June 15, 2009.
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 | Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved. Read more |
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| Architecture. McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc. All rights reserved. Read more |
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| Archaeology Dictionary. The Concise Oxford Dictionary of Archaeology. Copyright © 2002, 2003 by Oxford University Press. All rights reserved. Read more |
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