In photography, a glass is defined as a chemical Bath used to change the hue of prints.

See also:
"Glass" is in the NAICS Code "238150"
  (Glass and Glazing ContractorsGlass cladding (i.e., curtain wall), installation)

"Glass" is in the CPC Code "37111"
  Glass in the mass, in balls (except microspheres), rods or tubes, unworked; waste and scrap of glass