Colored photochromic glasses and method

A method for producing a permanent coloration in a surface zone on a photochromic glass article wherein silver halide is the photochromic agent, wherein the glass composition contains at least 1% by weight Li.sub.2 O, at least 2% by weight Na.sub.2 O, and at least 6% by weight Li.sub.2 O+Na.sub.2 O+K.sub.2 O, and wherein the glass article is heat treated at a temperature not exceeding about 450.degree. C. under reducing conditions for a time at least sufficient to modify the light absorption characteristics of the article surface, the improvement comprising shifting the optical absorption band imparted to the article during the reduction treatment by (1) changing the content of said Na.sub.2 O in at least a portion of the surface coloration zone of the article by exchanging lithium ions and potassium ions from within the glass surface sodium ions from an external source, said exchanging being effected prior to said reduction treatment and by (2) controlling the conditions of and the extent of ion exchange such that said shifting will be effected to provide a new absorption band.