MICROSHEET, SIMULTANEOUS HEAT TREATMENT, PHOTOCHROMIC GLASS SUITABLE FOR FORMATION AND GLASS SHEET FORMATION

摘要

The instant invention is directed to the production of photochromic glasses having compositions consisting essentially, as analyzed in weight percent on the oxide basis, ofPPSiO. sub.2 --55-60P PAl.sub.2 O.sub.3 --9-10PP B.sub.2 O.sub.3 --19- 20. 5PP Li.sub.2 O--2-2.5P PNa.sub.2 O--2- 3 PPK.sub.2 O--6-7P P PbO--0.1-0.25P PAg--0.1-0.15PPCl--0. 3-0.5PPBr--0.05- 0.15PP CuO--0.0065-0. 01PPThe glasses are capable of being drawn into sheet and articles cut from the sheet simultaneously shaped and photochromic properties developed therein. The glasses display a clear luminous transmittance in excess of 90% when free from tint, a darkened luminous transmittance at 20° C. below 25% when free from tint, and a fading rate at 20° C. such that the glass demonstrates a faded luminous transmittance at least twice that of the darkened transmittance after a five-minute fading interval.