A glass code is a method of classifying
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) of ...
es for
optical
Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultraviole ...
use, such as the manufacture of
lenses
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''), ...
and
prisms. There are many different types of glass with different compositions and optical properties, and a glass code is used to distinguish between them.
There are several different glass classification schemes in use, most based on the catalogue systems used by glass manufacturers such as
Pilkington
Pilkington is a Japanese-owned glass-manufacturing company which is based in Lathom, Lancashire, United Kingdom. In the UK it includes several legal entities and is a subsidiary of Japanese company NSG Group.
Prior to its acquisition by NSG i ...
and
Schott Glass
Schott AG is a German multinational glass company specializing in the manufacture of glass and glass-ceramics. Headquartered in Mainz, Germany, it is owned by the Carl Zeiss Foundation. The company's founder and namesake, Otto Schott, is credi ...
. These tend to be based on the material composition, for example ''BK7'' is the Schott Glass classification of a common
borosilicate
Borosilicate glass is a type of glass with silica and boron trioxide as the main glass-forming constituents. Borosilicate glasses are known for having very low coefficients of thermal expansion (≈3 × 10−6 K−1 at 20 °C), ma ...
crown glass.
The international glass code is based on
U.S. military standard MIL-G-174, and is a six-digit number specifying the glass according to its
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 ...
''n''
d at the
Fraunhofer d- (or D
3-) line, 589.3 nm, and its
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'' ind ...
''V''
d also taken at that line. The resulting glass code is the value of ''n''
d-1 rounded to three digits, followed by ''V''
d rounded to three digits, with all decimal points ignored. For example, BK7 has ''n''
d = 1.5168 and ''V''
d = 64.17, giving a six-digit glass code of 517642.
Consequently, a linear approximation for the refractive index dispersion close that wavelength is given by:
::
where
is the wavelength in nanometers.
The following table shows some example glasses and their glass code. Note that the glass properties can vary slightly between different manufacturer types.
[http://www.oharacorp.com/pdf/cross-ref-2010.pdf ]
References
{{DEFAULTSORT:Glass Code
Optical materials
Glass engineering and science