Manufacturers of optical coatings and components

Schott KG series heat-absorbing glass is nearly colorless and ionically "colored" to absorb infrared radiation. Care must be used in high power systems, since rapid IR absorption causes a large enough temperature gradient through the filter to cause thermal stress fracture. This problem can be mitigated by the application of an optical thin film coating to the entrance surface.

All of the KG series glass is resistant to staining, but sensitive to attack by both acids and alkali.  KG3 and KG5 are the most sensitive to alkali.  KG5 is the most sensitive to acid attack also.   All KG series glass exhibits some tendency towards clouding of the polished surfaces under humid conditions.

Prolonged exposure of KG series glass 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.