A glass code is a method of classifying glasses 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 | nd | Vd | Glass Code | Manufacturer code | |||
|---|---|---|---|---|---|---|---|
| Schott | Pilkington | Hoya | Ohara | ||||
| Borosilicate crown | 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 |
Famous quotes containing the words glass and/or code:
“In the woods in a winter afternoon one will see as readily the origin of the stained glass window, with which Gothic cathedrals are adorned, in the colors of the western sky seen through the bare and crossing branches of the forest.”
—Ralph Waldo Emerson (1803–1882)
“...I had grown up in a world that was dominated by immature age. Not by vigorous immaturity, but by immaturity that was old and tired and prudent, that loved ritual and rubric, and was utterly wanting in curiosity about the new and the strange. Its era has passed away, and the world it made has crumbled around us. Its finest creation, a code of manners, has been ridiculed and discarded.”
—Ellen Glasgow (1873–1945)