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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.
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.
The noun has 2 meanings:
Meaning #1:
a glass blown into a globe which is later flattened and spun to form a disk
Meaning #2:
optical glass of low dispersion and low refractive index
Synonym: optical crown
Crown glass was an early type of window glass. In this process, glass was blown into a "crown" or hollow globe. This was 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.
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 bulls-eye, the center area 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.
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Copyrights:
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 | Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2007. 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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| WordNet. WordNet 1.7.1 Copyright © 2001 by Princeton University. All rights reserved. Read more |
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| Wikipedia. This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Crown glass (window)". Read more |
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