Colorless inorganic glass

Colourless inorganic glasses containing copper halides or copper cadmium halides and having a sharp optical absorption cutoff between 370 nm and 425 nm;

• consisting essentially of, expressed in cationic percentages:
• 23-73% SiO2 15-45% B2O3 0-24% Al2O3 0-12% Li2O 0-20% Na2O 0-12% K2O 0-5% CaO + BaO + SrO 0.125-1% Cu2O 0-1% CdO 0-5% ZrO2 with 0-1.75% Cl 0.25-2% Cl + Br and the weight content of 0-2% Br BR exceeding that of Cl (Br > Cl) and 0-2% F;
• the Cl, Br and F contents being expressed in percentages by weight of the total composition;
• with an effective amount of at least one reducing agent selected from SnO2, As2O3, Sb2O3 , and mixtures thereof, in order to have mainly, in said glasses, the copper in the form of cuprous ions (Cu+), and thereby providing glasses which have neither a red coloration, nor a blue green coloration;
• and having a minimal yellow coloration whereby they have, according to the Standard T 51-067 (NF):
• a yellow index of less than 1.3 for a 2 mm. thick glass having a UV cutoff wavelength at 1% transmission between 370 and 395 nm;
• a yellow index of less than 2.3 for a 2 mm. thick glass having a UV cutoff wavelength at 1% transmission at 400 nm;
• a yellow index of less than 4 for a glass having a UV cutoff wavelength at 1% transmission, at 405 nm;
• a yellow index of less than 20 for a glass having a UV cutoff wavelength at 1% transmission at 411 nm;
• a yellow index of less than 50 for a 2 mm. thick glass having a UV cutoff wavelength at 1% transmission at 415 nm.