Flint glass is optical

glass Glass is a non-crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling ( quenching ...

that has relatively high

refractive index In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium. The refractive index determines how much the path of light is bent, or ...

and low

Abbe number In optics and lens design, the Abbe number, also known as the V-number or constringence of a transparent material, is an approximate measure of the material's dispersion (change of refractive index versus wavelength), with high values of ''V'' in ...

(high dispersion). 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 and 2.00. A concave lens of flint glass is commonly combined with a

convex lens A lens is a transmissive optical device which focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements'') ...

of crown glass to produce an

achromatic doublet An achromatic lens or achromat is a lens that is designed to limit the effects of chromatic and spherical aberration. Achromatic lenses are corrected to bring two wavelengths (typically red and blue) into focus on the same plane. The most comm ...

lens because of their compensating

optical properties The optical properties of a material define how it interacts with light. The optical properties of matter are studied in optical physics, a subfield of optics. The optical properties of matter include: *Refractive index * Dispersion *Transmittance a ...

, which reduces

chromatic aberration In optics, chromatic aberration (CA), also called chromatic distortion and spherochromatism, is a failure of a lens to focus all colors to the same point. It is caused by dispersion: the refractive index of the lens elements varies with the w ...

(colour defects). With respect to glass, the term ''flint'' derives from the

flint Flint, occasionally flintstone, is a sedimentary cryptocrystalline form of the mineral quartz, categorized as the variety of chert that occurs in chalk or marly limestone. Flint was widely used historically to make stone tools and sta ...

nodules found in the chalk deposits of southeast England that were used as a source of high purity silica by George Ravenscroft, c. 1662, to produce a

potash Potash () includes various mined and manufactured salts that contain potassium in water-soluble form.

lead glass Lead glass, commonly called crystal, is a variety of glass in which lead replaces the calcium content of a typical potash glass. Lead glass contains typically 18–40% (by weight) lead(II) oxide (PbO), while modern lead crystal, historically al ...

that was the precursor to English lead crystal. Traditionally, flint glasses were

es containing around 4–60% lead(II) oxide; however, the manufacture and disposal of these glasses were sources of

pollution Pollution is the introduction of contaminants into the natural environment that cause adverse change. Pollution can take the form of any substance (solid, liquid, or gas) or energy (such as radioactivity, heat, sound, or light). Pollutants, the ...

. In many modern flint glasses, lead oxides are replaced with other metal oxides such as

titanium dioxide Titanium dioxide, also known as titanium(IV) oxide or titania , is the inorganic compound with the chemical formula . When used as a pigment, it is called titanium white, Pigment White 6 (PW6), or CI 77891. It is a white solid that is insolub ...

and

zirconium dioxide Zirconium dioxide (), sometimes known as zirconia (not to be confused with zircon), is a white crystalline oxide of zirconium. Its most naturally occurring form, with a monoclinic crystalline structure, is the mineral baddeleyite. A dopant stabi ...

without significantly altering the optical properties of the glass.

References

* {{Glass science Glass compositions Diamond simulants

See also

References