Manufacturers of optical coatings and components

Schott BG series filter glass appears dark blue, and transmits primarily UVA and blue light.

Most of the BG series glasses are resistant to staining, and not unusually susceptible to attack by acids or alkali.   The exceptions are as follows:

BG36, BG39, BG40 and BG24A are quite easily acid etched.  BG18, BG24A, BG38, BG39, BG40 and BG42 are more susceptible to attack by alkali than the rest of the BG series glass, with BG39 and BG40 being the most vulnerable.  Additionally, BG24A, BG39 and BG40 exhibit clouding of the polished surfaces after a few months, even during normal storage.

Prolonged exposure of BG3, BG12, BG20, BG23, BG24A, BG25, BG26, BG28 and BG34 filters to UV radiation, particularly l < 320 nm, causes an irreversible reduction in transmittance and a shift of the short wave cut on wavelength to shorter wavelengths.  This solarization effect is UV intensity dependent, and eventually saturates.  Note that BG14, BG25 and BG26 also solarize under the influence of UVA (315 - 380 nm).