Kinetics of bleaching of photochromic glass.

Glasses containing small particles of silver halide are caused to darken by the action of uv light. Fading occurs when the exciting light source is removed and is often enhanced by irradiation with visible light. It is shown that simultaneous optical and thermal bleaching can be separated mathematically and that optical bleaching is a first order process. A model for thermal bleaching based on diffusion is consistent with rate studies and qualitatively explains the dependence of the fading rate on the darkening conditions.