Crown glass (optics)

When soda lime glass is referred to in the production of color-corrected lenses all optical glasses with an Abbe number of greater than 50

Composition

• Quartz ( SiO2): about 73 %
• Sodium oxide ( Na2O): about 5 %
• Potassium oxide ( K2O): about 17 %
• Calcium oxide ( CaO): about 3%
• Aluminum oxide ( Al2O3): about 2%

Properties

Because of the high proportion of quartz crown glass is refractory. It has a refractive index having a value between 1.5 and 1.6 significantly lower than that of flint glass. With an Abbe number of about 60, typically its dispersion is relatively small.

Use

Soda lime glass is used for the production of higher quality glass products and a mirror glass.

Made of optical crown glass lenses and lenses for microscopes, telescopes, lenses and other optical instruments are made. In the achromat is the low dispersion of crown glass in conjunction with flint glass, which shows high dispersion, used for color correction.

History

Crown glass has been known for centuries. It takes its name obtained by the oldest method of window glass production in England. You took the melting river with the blowpipe the glass mass needed and blew it first a hollow sphere. Then the blowpipe was held up and turned quickly, with flattened ball. Then you put the blowpipe towards a punty and blew off the pipe, so that a circular hole was created. After re heating the pre-blown sphere was rotated with the punty.

Here, the opening enlarged; its edge bent outward by the centrifugal force around and took the form of a crown. By further turning a circular glass disc was used as a window pane after their separation from the clamping iron was formed. In old churches and houses can still be found in part such round, encased in lead glass. They are also called crown glass or slug.

• Optical glass