BG dispersion
The BG dispersion is a characteristic quantity of clear, non-scattering gemstones . It describes the difference between the refractive indices of two wavelengths that are in the red and blue spectral range. To measure the two refractive indices, wavelengths of the Fraunhofer lines are used:
- B-line (λ B = 686.719 nm)
- G line (λ G = 430.790 nm)
The determination of the value of the BG dispersion is a measurement method without destroying the test object and is therefore suitable for the identification of gemstones, crystals or minerals. In the jewelry industry, BG dispersion is known as fire .
Examples
| Type | BG dispersion |
|---|---|
| Rutile | 0.280 |
| Zirconia | 0.066 |
| Demantoid | 0.057 |
| Titanite | 0.051 |
| diamond | 0.044 |
| Zircon | 0.039 |
| ruby | 0.018 |
| quartz | 0.013 |
More rarely, one finds information on CF dispersion in the literature , which falls back on the Fraunhofer H lines:
- C line (λ C = 656.281 nm)
- F line (λ F = 486.134 nm)
literature
- Jean-Claude Boulliard: Pierres précieuses: Guide pratique d'identification . Publibook, Paris 2015, ISBN 978-2-342-04013-5 .
- Walter Schumann: Precious stones and gemstones. All species and varieties in the world. 1900 unique pieces . BLV Verlag, Munich, 14th, expanded and updated edition 2008, ISBN 978-3-8354-0408-3 .