Method of making colored photochromic glasses

Claim 1

A method for producing different shades of a yellow to orange tint in a surface layer in a transparent photochromic glass article, the differences in shade being due to a major variation in luminous transmittance of the glass with a minor shift in the chromaticity thereof and the hues of which will remain essentially unchanged after subsequent heat treatments up to about the strain point of the glass, said photochromic glass containing crystals selected from the group of silver chloride, silver bromide, and silver iodide as the photochromic agents and containing at least 0.5% lead, expressed as PbO, in the composition thereof, said method comprising exposing at least a portion of said photochromic article to a gaseous reducing environment at a temperature ranging from about the strain point to about 50° C. above the annealing point of the glass for a time of at least 0.5 hour to cause in the surface of said glass silver ions to be reduced to metallic silver particles and lead ions to be reduced to metallic lead particles which either coat or alloy with the metallic silver.

Claim 2

A method for producing different shades of a yellow to orange tint in a surface layer in a transparent photochromic glass article, the differences in shade being due to a major variation in luminous transmittance of the glass with a minor shift in the chromaticity thereof and the hues of which will remain essentially unchanged after subsequent heat treatments up to about the strain point of the glass, said photochromic glass containing crystals selected from the group of silver chloride, silver bromide, and silver iodide as the photochromic agents and containing at least 0.5% lead, expressed as PbO, in the composition thereof, said method comprising exposing at least a portion of said photochromic article to a gaseous reducing environment at a temperature ranging from about the strain point to about 50° C. above the annealing point of the glass for a time of at least 0.5 hour to cause in the surface of said glass silver ions to be reduced to metallic silver particles and lead ions to be reduced to metallic lead particles which either coat or alloy with the metallic silver.

Claim 8

A method for producing different shades of a yellow to orange tint in a surface layer in transparent photochromic glass articles, said differences in shade being due to a major variation in luminous transmittance of the glass with a minor shift in the chromaticity thereof and the hues of which will remain essentially unchanged even after subsequent heat treatments up to about the strain point of the glass, said photochromic glass being highly absorbing of ultraviolet radiations and the blue portion of the visible spectrum and containing crystals selected from the group of silver chloride, silver bromide, and silver iodide as the photochromic agents and containing at least 0.5% lead, expressed as PbO, in the composition thereof, said method comprising the steps of: (a) exposing at least a portion of said photochromic glass article to a gaseous reducing environment at a temperature below the strain point of said glass for a time sufficient to cause silver ions in the surface of said glass to be reduced to metallic silver particles, and, thereafter, (b) subjecting said previously-exposed portion of said photochromic glass article to a gaseous reducing environment at a temperature ranging from about the strain point of the glass to about 50° C. above the annealing point of the glass for a time of at least 0.5 hour to cause the reduction of lead ions in the surface of said glass to metallic lead particles as a layer over the metallic silver particles.

Claim 9

A method for producing different shades of a yellow to orange tint in a surface layer in transparent photochromic glass articles, said differences in shade being due to a major variation in luminous transmittance of the glass with a minor shift in the chromaticity thereof and the hues of which will remain essentially unchanged even after subsequent heat treatments up to about the strain point of the glass, said photochromic glass being highly absorbing of ultraviolet radiations and the blue portion of the visible spectrum and containing crystals selected from the group of silver chloride, silver bromide, and silver iodide as the photochromic agents and containing at least 0.5% lead, expressed as PbO, in the composition thereof, said method comprising the steps of: (a) exposing at least a portion of said photochromic glass article to a gaseous reducing environment at a temperature below the strain point of said glass for a time sufficient to cause silver ions in the surface of said glass to be reduced to metallic silver particles, and, thereafter, (b) subjecting said previously-exposed portion of said photochromic glass article to a gaseous reducing environment at a temperature ranging from about the strain point of the glass to about 50° C. above the annealing point of the glass for a time of at least 0.5 hour to cause the reduction of lead ions in the surface of said glass to metallic lead particles as a layer over the metallic silver particles.