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:
“The awaited scream rises,
the shattering
of glass and the cracking
of bone
a polar tumult as when
black ice booms....”
—Denise Levertov (b. 1923)
“Many people will say to working mothers, in effect, “I don’t think you can have it all.” The phrase for “have it all” is code for “have your cake and eat it too.” What these people really mean is that achievement in the workplace has always come at a price—usually a significant personal price; conversely, women who stayed home with their children were seen as having sacrificed a great deal of their own ambition for their families.”
—Anne C. Weisberg (20th century)