Flint glass
Encyclopedia
Flint glass is 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 and 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, which reduces chromatic aberration
(color defects).
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 precursor to English lead crystal.
Traditionally, flint glasses were lead glass
es containing 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.
Flint glass can be fashioned into rhinestone
s which are used as diamond simulant
s.
Glass
Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...
that has relatively high refractive index
Refractive index
In optics the refractive index or index of refraction of a substance or medium is a measure of the speed of light in that medium. It is expressed as a ratio of the speed of light in vacuum relative to that in the considered medium....
and low Abbe number
Abbe number
In physics and optics, the Abbe number, also known as the V-number or constringence of a transparent material, is a measure of the material's dispersion in relation to the refractive index...
. 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 of crown glass
Crown glass (optics)
Crown glass is type of optical glass used in lenses and other optical components. It has relatively low refractive index and low dispersion...
to produce an achromatic doublet lens because of their compensating optical properties, which reduces chromatic aberration
Chromatic aberration
In optics, chromatic aberration is a type of distortion in which there is a failure of a lens to focus all colors to the same convergence point. It occurs because lenses have a different refractive index for different wavelengths of light...
(color defects).
With respect to glass, the term flint derives from the flint
Flint
Flint is a hard, sedimentary cryptocrystalline form of the mineral quartz, categorized as a variety of chert. It occurs chiefly as nodules and masses in sedimentary rocks, such as chalks and limestones. Inside the nodule, flint is usually dark grey, black, green, white, or brown in colour, and...
nodules found in the chalk deposits of southeast England that were used as a source of high purity silica by George Ravenscroft
George Ravenscroft
George Ravenscroft was an English businessman in the import/export and glass making trades. He is primarily known for his work in developing clear lead crystal glass in England.-Personal life:...
, circa 1662, to produce a potash
Potash
Potash is the common name for various mined and manufactured salts that contain potassium in water-soluble form. In some rare cases, potash can be formed with traces of organic materials such as plant remains, and this was the major historical source for it before the industrial era...
lead glass
Lead glass
Lead glass is a variety of glass in which lead replaces the calcium content of a typical potash glass. Lead glass contains typically 18–40 weight% lead oxide , while modern lead crystal, historically also known as flint glass due to the original silica source, contains a minimum of 24% PbO...
that was the precursor to English lead crystal.
Traditionally, flint glasses were lead glass
Lead glass
Lead glass is a variety of glass in which lead replaces the calcium content of a typical potash glass. Lead glass contains typically 18–40 weight% lead oxide , while modern lead crystal, historically also known as flint glass due to the original silica source, contains a minimum of 24% PbO...
es containing around 4–60% lead oxide
Lead oxide
Lead oxide may refer to:* Lead oxide, PbO, litharge, massicot* Lead oxide, Pb3O4, minium, red lead* Lead dioxide , PbO2Less common lead oxides are:* Lead oxide, Pb2O3, lead sesquioxide...
; however, the manufacture and disposal of these glasses are sources of pollution
Pollution
Pollution is the introduction of contaminants into a natural environment that causes instability, disorder, harm or discomfort to the ecosystem i.e. physical systems or living organisms. Pollution can take the form of chemical substances or energy, such as noise, heat or light...
. In many modern flint glasses, the lead can be replaced with other additives such as titanium dioxide
Titanium dioxide
Titanium dioxide, also known as titanium oxide or titania, is the naturally occurring oxide of titanium, chemical formula . When used as a pigment, it is called titanium white, Pigment White 6, or CI 77891. Generally it comes in two different forms, rutile and anatase. It has a wide range of...
and zirconium dioxide
Zirconium dioxide
Zirconium dioxide , sometimes known as zirconia , is a white crystalline oxide of zirconium. Its most naturally occurring form, with a monoclinic crystalline structure, is the rare mineral baddeleyite. The high temperature cubic crystalline form is rarely found in nature as mineral tazheranite O2...
without significantly altering the optical properties of the glass.
Flint glass can be fashioned into rhinestone
Rhinestone
A rhinestone or paste or diamante is a diamond simulant made from rock crystal, glass or acrylic.Originally, rhinestones were rock crystals gathered from the river Rhine. The availability was greatly increased around 1775 when the Alsatian jeweller Georg Friedrich Strass had the idea to imitate...
s which are used as diamond simulant
Diamond simulant
The high price of gem-grade diamonds, as well as significant ethical concerns of the diamond trade, have created a large demand for materials with similar gemological characteristics, known as diamond simulants or imitations. Simulants are distinct from synthetic diamond, which unlike simulants is...
s.