Abstract: The instant invention relates to the production of crystal-free, transparent glass articles which emit a strong bluish luminescence when excited by either ultraviolet or cathode rays. Such glass articles are prepared from aluminosilicate compositions which consist essentially, in terms of mole percent on the oxide basis, of about 15-30% Al.sub.2 O.sub.3 and 45-70% SiO.sub.2, the sum of those two components constituting at least 75 mole percent, but no more than about 95 mole percent, of the total composition, and 0.025-2% europium, expressed as Eu.sub.2 O.sub.3. The remainder of the composition is generally made up of compatible monovalent, divalent, and/or trivalent modifying oxides. The desired high degree of luminescence is brought about by exposing the glass articles to a reducing atmosphere at a temperature below the softening point of the glass.