Importance

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Abstract

A process for producing a photochromic glass which will exhibit a brown coloration in its darkened state without a degradation in the photochromic properties of the glass taking place. The process includes the steps of forming a batch of specified components which include tin or a tin compound and subjecting the resultant batch to a series of glass-forming steps so as to develop photochromic properties in a glass article formed from the molten batch. The invention also provides a photochromic glass having silver halide crystals and tin dispersed throughout the glass, the glass having in its darkened state a brown coloration which is described in accordance with the Hunter L,a,b, Color Scale System by the rectangular region having corners defined by the (a,b) co-ordinates: (5,1), (1,5), (12,16) and (16,12), the 1/2 OD FT of the glass being 120 seconds or less.

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First Claim