Glass code
Encyclopedia
A glass code is a method of classifying glass
es for optical
use, such as the manufacture of lenses
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
and Schott Glass
. These tend to be based on the material composition, for example BK7 is the Schott Glass classification of a common borosilicate
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
nd at the Fraunhofer d- (or D3-) line, and its Abbe number
Vd also taken at that line.
The resulting glass code is the value of nd-1 rounded to three digits, followed by Vd rounded to three digits, with all decimal points ignored. For example, BK7 has nd = 1.5168 and Vd = 64.17, giving a six-digit glass code of 517642.
The following table shows some example glasses and their glass code. Note that the glass properties can vary slightly between different manufacturer types.
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...
es for optical
Optics
Optics is the branch of physics which involves the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behavior of visible, ultraviolet, and infrared light...
use, such as the manufacture of lenses
Lens (optics)
A lens is an optical device with perfect or approximate axial symmetry which transmits and refracts light, converging or diverging the beam. A simple lens consists of a single optical element...
and prisms
Prism (optics)
In optics, a prism is a transparent optical element with flat, polished surfaces that refract light. The exact angles between the surfaces depend on the application. The traditional geometrical shape is that of a triangular prism with a triangular base and rectangular sides, and in colloquial use...
. 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
Pilkington Group Limited is a multinational glass manufacturing company headquartered in St Helens, United Kingdom. It is a subsidiary of the Japan-based NSG Group...
and Schott Glass
Schott Glass
SCHOTT AG is a German manufacturer of high-quality industrial glass products, its main markets are household appliances, pharmaceutical industries, solar energy, electronics, optics as well as automotive...
. These tend to be based on the material composition, for example BK7 is the Schott Glass classification of a common borosilicate
Borosilicate glass
Borosilicate glass is a type of glass with the main glass-forming constituents silica and boron oxide. Borosilicate glasses are known for having very low coefficients of thermal expansion , making them resistant to thermal shock, more so than any other common glass...
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...
.
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
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....
nd at the Fraunhofer d- (or D3-) line, and its 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...
Vd also taken at that line.
The resulting glass code is the value of nd-1 rounded to three digits, followed by Vd rounded to three digits, with all decimal points ignored. For example, BK7 has nd = 1.5168 and Vd = 64.17, giving a six-digit glass code of 517642.
The following table shows some example glasses and their glass code. Note that the glass properties can vary slightly between different manufacturer types.
| Glass | nd | Vd | Glass Code | Manufacturer code | |||
|---|---|---|---|---|---|---|---|
| Schott | Pilkington | Hoya | Ohara | ||||
| Borosilicate crown Borosilicate glass Borosilicate glass is a type of glass with the main glass-forming constituents silica and boron oxide. Borosilicate glasses are known for having very low coefficients of thermal expansion , making them resistant to thermal shock, more so than any other common glass... |
1.5168 | 64.17 | 517642 | BK7 | BSC517642 | BSC7 | S-BSL7 |
| Barium crown | 1.5688 | 56.05 | 569561 | BaK4 | MBC569561 | BaC4 | S-BAL14 |
| Dense crown | 1.6204 | 60.32 | 620603 | SK16 | DBC620603 | BaCD16 | S-BSM16 |
| Lanthanum flint | 1.7439 | 44.85 | 744448 | LaF2 | LAF744447 | LaF2 | S-LAM2 |
| Dense flint | 1.7847 | 25.76 | 785258 | SF11 | DEDF785258 | FD11 | S-TIH11 |