Photochromic particle consisting of agx crystal with an inorganic oxide coating

Abstract From the Canadian patent

Photochromic particles which are particularly useful in ophthalmic quality plastic host materials are formed of a silver halide crystal whose dimensions lie generally in the range between 30 Angstroms and 2500 Angstroms. The entire surface of the silver halide crystal is located with a material whose properties and thickness are effective to render the coating impervious to halogen diffusion and interaction with host material. The coated particles may then be introduced by known schemes into standard plastic host materials in order to form photochromic plastic materials.