Bubble & Inclusion

It is most desirable to manufacture bubble-free optical glass, but the existence of bubbles to some extent is inevitable. Bubbles in optical glass vary in size and number from one glass to another due to the many different compositions and production methods. Glass types which tend to contain relatively more bubbles than usual glass types are marked " B ". Inclusions such as small stones or crystals are treated as bubbles.

Coloring

Coloring can be determined by measuring spectral transmission, including reflection losses with test pieces of 10 mm in thickness. The wavelengths corresponding to 80% transmission and 5% transmission are indicated as 405/355 in units of 5nm, after rounding off 2 and rounding up 3 or more and rounding off 7 and rounding up 8 or more.
For glass types with a high refractive index of n_e≥1.85, the wavelength showing transmittance of 70% was used instead of 80%, because the reflection loss is large. The indication has been made as (415).

Specific Gravity* (d)

Specific gravity is the density value of well-annealed glass referenced against pure water at 4 °C , with the value shown to the second decimal place.