Flint glass is an optical glass that has relatively high refractive index and low Abbe number. Flint glasses are arbitrarily defined as having an Abbe number of 50 to 55 or less. The currently known flint glasses have refractive indices ranging between 1.45-2.00. A concave lens of flint glass is commonly combined with a convex lens of crown glass to produce an achromatic doublet lens because of their compensating optical properties. Glass can be made transparent and flat, or into other shapes and colors as shown in this sphere from the Verrerie of Brehat in Brittany. ... The refractive index (or index of refraction) of a material is the factor by which the phase velocity of electromagnetic radiation is slowed in that material, relative to its velocity in a vacuum. ... In physics and optics, the Abbe number, also known as the V-number or constringence of a transparent material is a measure of the materials dispersion (variation of refractive index with wavelength). ... A lens. ... A lens. ... Crown glass is a type of optical glass used in lenses. ...

With respect to glass, the term "flint" derives from the flint nodules found in the chalk deposits of southeast England that were used as a source of high purity silica by George Ravenscroft, circa 1662, to produce a potash lead glass that was the predecessor to English lead crystal. A flint nodule from the Onondaga limestone layer, Buffalo, New York. ... Potash Potash (or carbonate of potash) is an impure form of potassium carbonate (K2CO3) mixed with other potassium salts. ... Lead glass is potassium silicate glass which has been impregnated with lead oxide (from 12% to 28% by weight) in its fabrication. ...

Traditionally, flint glasses contain around 4%—60% lead oxide, however the manufacture and disposal of these glasses are sources of pollution. In many modern flint glasses, the lead can be replaced with other additives such as titanium dioxide and zirconium dioxide without significantly altering the optical properties of the glass. Lead(II) oxide or litharge is a yellow oxide of lead of formula PbO, created by heating lead in air. ... It has been suggested that Externality be merged into this article or section. ... Titanium dioxide, also known as titanium(IV) oxide or titania, is the naturally occurring oxide of titanium, chemical formula TiO2. ... Zirconium dioxide (ZrO2), sometimes known as zirconia, is a white crystalline oxide of zirconium. ...

Flint glass can be fashioned into rhinestones which are used as diamond simulants. A rhinestone or paste is a diamond simulant made from rock crystal, glass or acrylic. ... Due to its low cost and close visual likeness to diamond, cubic zirconia has remained the most gemologically and economically important diamond simulant since 1976. ...

See also

• Crown glass (optics)
• Chromatic aberration

Crown glass is a type of optical glass used in lenses. ... Chromatic aberration is caused by the dispersion of the lens material, the variation of its refractive index n with the wavelength of light. ...

References

• Kurkjian, Charles R. and Prindle, William R. (1998). Perspectives on the History of Glass Composition. Journal of the American Ceramic Society, 81 (4), 795-813.