What is "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. Cornice, Corona, Coroner, Coronet.]

1. A wreath or garland, or any ornamental fillet encircling the head, especially as a reward of victory or mark of honorable distinction; hence, anything given on account of, or obtained by, faithful or successful effort; a reward. ``An olive branch and laurel crown.''
   --Shak.

   They do it to obtain a corruptible crown; but we an incorruptible.
   --1 Cor. ix. 25.

   Be thou faithful unto death, and I will give thee a crown of life.
   --Rev. ii. 10.

2. A royal headdress or cap of sovereignty, worn by emperors, kings, princes, etc.

   Note: Nobles wear coronets; the triple crown of the pope is usually called a tiara. The crown of England is a circle of gold with crosses, fleurs-de-lis, and imperial arches, inclosing a crimson velvet cap, and ornamented with thousands of diamonds and precious stones.

3. The person entitled to wear a regal or imperial crown; the sovereign; -- with the definite article.

   Parliament may be dissolved by the demise of the crown.
   --Blackstone.

   Large arrears of pay were due to the civil and military servants of the crown.
   --Macaulay.

4. Imperial or regal power or dominion; sovereignty.

   There is a power behind the crown greater than the crown itself.
   --Junius.

5. Anything which imparts beauty, splendor, honor, dignity, or finish.

   The hoary head is a crown of glory, if it be found in the way of righteousness.
   --Prov. xvi. 31.

   A virtuous woman is a crown to her husband.
   --Prov. xvi. 4.

6. Highest state; acme; consummation; perfection.

   Mutual love, the crown of all our bliss.
   --Milton.

7. The topmost part of anything; the summit.

   The steepy crown of the bare mountains.
   --Dryden.

8. The topmost part of the head (see Illust. of Bird.); that part of the head from which the hair descends toward the sides and back; also, the head or brain.

   From toe to crown he'll fill our skin with pinches.
   --Shak.

   Twenty things which I set down: This done, I twenty more-had in my crown.
   --Bunyan.

9. The part of a hat above the brim.

10. (Anat.) The part of a tooth which projects above the gum; also, the top or grinding surface of a tooth.

11. (Arch.) The vertex or top of an arch; -- applied generally to about one third of the curve, but in a pointed arch to the apex only.

12. (Bot.) Same as Corona.

13. (Naut.)

    1. That part of an anchor where the arms are joined to the shank.

    2. The rounding, or rounded part, of the deck from a level line.

    3. pl. The bights formed by the several turns of a cable.
       --Totten.

14. The upper range of facets in a rose diamond.

15. The dome of a furnace.

16. (Geom.) The area inclosed between two concentric perimeters.

17. (Eccl.) A round spot shaved clean on the top of the head, as a mark of the clerical state; the tonsure.

18. A size of writing paper. See under Paper.

19. A coin stamped with the image of a crown; hence,a denomination of money; as, the English crown, a silver coin of the value of five shillings sterling, or a little more than $1.20; the Danish or Norwegian crown, a money of account, etc., worth nearly twenty-seven cents.

20. An ornaments or decoration representing a crown; as, the paper is stamped with a crown.

    Crown of aberration (Astron.), a spurious circle around the true circle of the sun.

    Crown antler (Zo["o]l.), the topmost branch or tine of an antler; also, an antler having a cuplike top, with tines springing from the rim.

    Crown bar, one of the bars which support the crown sheet of steam-boiler furnace.

    Crown glass. See under Glass.

    Crown imperial. (Bot.) See in the Vocabulary.

    Crown jewels, the jewels appertaining to the sovereign while wearing the crown. [Eng.] ``She pawned and set to sale the crown jewels.''
    --Milton.

    Crown land, land belonging to the crown, that is, to the sovereign.

    Crown law, the law which governs criminal prosecutions.

    Crown lawyer, one employed by the crown, as in criminal cases. [Eng.]

    Crown octavo. See under Paper.

    Crown office. See in the Vocabulary.

    Crown paper. See under Paper.

    Crown piece. See in the Vocabulary.

    Crown Prince, the heir apparent to a crown or throne.

    Crown saw. See in the Vocabulary.

    Crown scab (Far.), a cancerous sore formed round the corners of a horse's hoof.

    Crown sheet, the flat plate which forms the top of the furnace or fire box of an internally fired steam boiler.

    Crown shell. (Zo["o]l.) See Acorn-shell.

    Crown side. See Crown office.

    Crown tax (Eccl. Hist.), a golden crown, or its value, which was required annually from the Jews by the king of Syria, in the time of the Maccabees.
    --1 Macc. x. 20.

    Crown wheel. See in the Vocabulary.

    Crown work. See in the Vocabulary.

    Pleas of the crown (Engl. law), criminal actions.

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.]

1. A hard, brittle, translucent, and commonly transparent substance, white or colored, having a conchoidal fracture, and made by fusing together sand or silica with lime, potash, soda, or lead oxide. It is used for window panes and mirrors, for articles of table and culinary use, for lenses, and various articles of ornament.

   Note: Glass is variously colored by the metallic oxides; thus, manganese colors it violet; copper (cuprous), red, or (cupric) green; cobalt, blue; uranium, yellowish green or canary yellow; iron, green or brown; gold, purple or red; tin, opaque white; chromium, emerald green; antimony, yellow.

2. (Chem.) Any substance having a peculiar glassy appearance, and a conchoidal fracture, and usually produced by fusion.

3. Anything made of glass. Especially:

   1. A looking-glass; a mirror.

   2. A vessel filled with running sand for measuring time; an hourglass; and hence, the time in which such a vessel is exhausted of its sand.

      She would not live The running of one glass.
      --Shak.

   3. A drinking vessel; a tumbler; a goblet; hence, the contents of such a vessel; especially; spirituous liquors; as, he took a glass at dinner.

   4. An optical glass; a lens; a spyglass; -- in the plural, spectacles; as, a pair of glasses; he wears glasses.

   5. A weatherglass; a barometer. Note: Glass is much used adjectively or in combination; as, glass maker, or glassmaker; glass making or glassmaking; glass blower or glassblower, etc. Bohemian glass, Cut glass, etc. See under Bohemian, Cut, etc. Crown glass, a variety of glass, used for making the finest plate or window glass, and consisting essentially of silicate of soda or potash and lime, with no admixture of lead; the convex half of an achromatic lens is composed of crown glass; -- so called from a crownlike shape given it in the process of blowing. Crystal glass, or Flint glass. See Flint glass, in the Vocabulary. Cylinder glass, sheet glass made by blowing the glass in the form of a cylinder which is then split longitudinally, opened out, and flattened. Glass of antimony, a vitreous oxide of antimony mixed with sulphide. Glass cloth, a woven fabric formed of glass fibers. Glass coach, a coach superior to a hackney-coach, hired for the day, or any short period, as a private carriage; -- so called because originally private carriages alone had glass windows. [Eng.] --Smart. Glass coaches are [allowed in English parks from which ordinary hacks are excluded], meaning by this term, which is never used in America, hired carriages that do not go on stands. --J. F. Cooper. Glass cutter.

      1. One who cuts sheets of glass into sizes for window panes, ets.

      2. One who shapes the surface of glass by grinding and polishing.

      3. A tool, usually with a diamond at the point, for cutting glass. Glass cutting.

         1. The act or process of dividing glass, as sheets of glass into panes with a diamond.

         2. The act or process of shaping the surface of glass by appylying it to revolving wheels, upon which sand, emery, and, afterwards, polishing powder, are applied; especially of glass which is shaped into facets, tooth ornaments, and the like. Glass having ornamental scrolls, etc., cut upon it, is said to be engraved.

            Glass metal, the fused material for making glass.

            Glass painting, the art or process of producing decorative effects in glass by painting it with enamel colors and combining the pieces together with slender sash bars of lead or other metal. In common parlance, glass painting and glass staining (see Glass staining, below) are used indifferently for all colored decorative work in windows, and the like.

            Glass paper, paper faced with pulvirezed glass, and used for abrasive purposes.

            Glass silk, fine threads of glass, wound, when in fusion, on rapidly rotating heated cylinders.

            Glass silvering, the process of transforming plate glass into mirrors by coating it with a reflecting surface, a deposit of silver, or a mercury amalgam.

            Glass soap, or Glassmaker's soap, the black oxide of manganese or other substances used by glass makers to take away color from the materials for glass.

            Glass staining, the art or practice of coloring glass in its whole substance, or, in the case of certain colors, in a superficial film only; also, decorative work in glass. Cf. Glass painting.

            Glass tears. See Rupert's drop.

            Glass works, an establishment where glass is made.

            Heavy glass, a heavy optical glass, consisting essentially of a borosilicate of potash.

            Millefiore glass. See Millefiore.

            Plate glass, a fine kind of glass, cast in thick plates, and flattened by heavy rollers, -- used for mirrors and the best windows.

            Pressed glass, glass articles formed in molds by pressure when hot.

            Soluble glass (Chem.), a silicate of sodium or potassium, found in commerce as a white, glassy mass, a stony powder, or dissolved as a viscous, sirupy liquid; -- used for rendering fabrics incombustible, for hardening artificial stone, etc.; -- called also water glass.

            Spun glass, glass drawn into a thread while liquid.

            Toughened glass, Tempered glass, glass finely tempered or annealed, by a peculiar method of sudden cooling by plunging while hot into oil, melted wax, or paraffine, etc.; -- called also, from the name of the inventor of the process, Bastie glass.

            Water glass. (Chem.) See Soluble glass, above.

            Window glass, glass in panes suitable for windows.

n. A variety of glass, used for making the finest plate or window glass, and consisting essentially of silicate of soda or potash and lime, with no admixture of lead.

1. n. a glass blown into a globe which is later flattened and spun to form a disk

2. optical glass of low dispersion and low refractive index [syn: optical crown]

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.

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.

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 punty mark was used for less expensive windows. In order to fill large window spaces with the best glass, many small diamond shapes would be cut from the edge of the disk and these would be 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. The process was first perfected by French glassmakers in the 1320s, notably around Rouen, and was a 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.

Crown glass is a type of optical glass used in lenses and other optical components. It has relatively low refractive index (≈1.52) and low dispersion (with Abbe numbers around 60). Crown glass is produced from alkali-lime (RCH) silicates containing approximately 10% potassium oxide and is one of the earliest low dispersion glasses.

As well as the specific material named crown glass, there are other optical glasses with similar properties that are also called crown glasses. Generally, this is any glass with Abbe numbers in the range 50 to 85. For example, the borosilicate glass Schott BK7 is an extremely common crown glass, used in precision lenses. Borosilicates contain about 10% boric oxide, have good optical and mechanical characteristics, and are resistant to chemical and environmental damage. Other additives used in crown glasses include zinc oxide, phosphorus pentoxide, barium oxide, fluorite and lanthanum oxide.

A concave lens of flint glass is commonly combined with a convex lens of crown glass to produce an achromatic doublet. The dispersions of the glasses partially compensate for each other, producing reduced chromatic aberration compared to a singlet lens with the same focal length.