Production of colored glass bodies

Claim 1

A process for imparting a desired coloration to a body of ordinary soda-lime-silica glass which is free of phosphorus pentoxide and formed from a vitrifiable composition, by diffusing a substance into surface layers of the body from a medium contacting the body, comprising the steps of: introducing a reducing agent into such surface layers by diffusion starting from the outer surface of the body, to cause such agent to be concentrated in such layers in an amount of at least 1% by weight; placing the body surface, after said step of introducing, into contact with such a medium composed of a mixture of (a) a salt furnishing reducible silver metal ions in an amount sufficient to impart coloration to the body, and capable of being reduced by the reducing agent and (b) a diluting agent constituted by a salt of another metal, furnishing metal ions which diffuse into the body in exchange for smaller ions initially present in the body, the total concentration in the medium of the salt furnishing reducible silver metal ions being less than one hundred parts per million; and during said step of placing, maintaining the surface layers at a temperature which causes such reducible silver metal ions to diffuse into the body surface layers and to be chemically reduced by the reducing agent and such ion exchange to induce in surface layers of the body compressive stresses which are prevented from relaxing entirely during the course of said step of placing, said diffusion of reducible silver metal ions and said ion exchange occurring similtaneously.