crown glass

crown glass
1. an optical glass of low dispersion and generally low index of refraction.
2. an old form of window glass formed by blowing a globe and whirling it into a disk.

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      handmade glass of soda-lime composition for domestic glazing or optical uses. The technique of crown glass remained standard from the earliest times: a bubble of glass, blown into a pear shape and flattened, was transferred to the glassmaker's pontil (a solid iron rod), reheated and rotated at speed, until centrifugal force formed a large circular plate of up to 60 inches in diameter. The finished “table” of glass was thin, lustrous, highly polished (by “fire-polish”), and had concentric ripple lines, the result of spinning; crown glass was slightly convex, and in the centre of the crown was the bull's eye, a thickened part where the pontil was attached. This was often cut out as a defect, but later it came to be prized as evidence of antiquity. Nevertheless, and despite the availability of cheaper cylinder glass (cast and rolled glass had been invented in the 17th century), crown glass was particularly popular for its superior quality and clarity. The crown process, which may have been Syrian in origin, was in use in Europe since at least the 14th century, when the industry was centred in Normandy, where a few families of glassblowers monopolized the trade and enjoyed a kind of aristocratic status. From about the mid-17th century the crown glass process was gradually replaced by easier methods of manufacturing larger glass sheets. Window glass of note, however, was made by this method in the U.S. by the Boston Crown Glass Company from 1793 to about 1827.

      Crown glass has optical properties that complement those of the denser flint glass when the two kinds are used together to form lenses corrected for chromatic aberration. Special ingredients may be added to crown glass to achieve particular optical qualities.

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Universalium. 2010.

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  • crown-glass — [ kronglas ] n. m. inv. • 1764; mots angl. « verre de couronne » ♦ Opt. Verre très transparent et peu dispersif servant à faire des lentilles d optique. ⇒CROWN GLASS, subst. masc. Verre blanc de qualité supérieure, employé pour la fabrication de… …   Encyclopédie Universelle

  • Crown glass — Glass Glass (gl[.a]s), n. [OE. glas, gles, AS. gl[ae]s; akin to D., G., Dan., & Sw. glas, Icel. glas, gler, Dan. glar; cf. AS. gl[ae]r amber, L. glaesum. Cf. {Glare}, n., {Glaze}, v. t.] [1913 Webster] 1. A hard, brittle, translucent, and… …   The Collaborative International Dictionary of English

  • Crown glass — Crown Crown (kroun), n. [OE. corone, coroun, crune, croun, OF. corone, corune, F. couronne, fr. L. corona crown, wreath; akin to Gr. korw nh anything curved, crown; cf. also L. curvus curved, E. curve, curb, Gael. cruinn round, W. crwn. Cf.… …   The Collaborative International Dictionary of English

  • Crown glass — is either of two kinds of glass: Crown glass (window) was a type of hand blown window glass. Crown glass (optics) is a type of optical glass used in lenses. This disambiguation page lists articles associated with the same title. If an …   Wikipedia

  • crown glass — crown′ glass n. 1) opt cer an optical glass of low dispersion and generally low index of refraction 2) cer an old form of window glass formed by blowing a globe and whirling it into a disk • Etymology: 1700–10 …   From formal English to slang

  • crown glass — n. 1. window glass made in flat, circular plates by blowing and whirling, with a small knot in the center left by the blower s rod 2. a very clear optical glass with a low index of refraction …   English World dictionary

  • crown glass — noun 1. a glass blown into a globe which is later flattened and spun to form a disk • Hypernyms: ↑glass 2. optical glass of low dispersion and low refractive index • Syn: ↑optical crown, ↑optical crown glass • Hypernyms: ↑optical glass …   Useful english dictionary

  • crown-glass — (krôn glas ) s. m. Espèce de verre constitué par 1 atome quadrisilicate de potasse et 1 atome quadrisilicate de chaux. C est un verre blanc de la plus belle qualité, qui est employé dans les lunettes achromatiques. ÉTYMOLOGIE    Angl. crown glass …   Dictionnaire de la Langue Française d'Émile Littré

  • crown glass — kronas statusas T sritis chemija apibrėžtis Optinis stiklas, turintis didelį lūžio rodiklį ir nedidelę sklaidą. atitikmenys: angl. crown glass rus. крон …   Chemijos terminų aiškinamasis žodynas

  • Crown glass (optics) — This article is about crown glass as used in optics. For the window glass, see Crown glass (window). Crown glass is type of optical glass used in lenses and other optical components. It has relatively low refractive index (≈1.52) and low… …   Wikipedia

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