Abstract: In the coloring of bodies of glass by diffusion of coloring ions from a treatment medium into surface layers thereof, the repeatability of the resulting coloration is improved by controlling not only the treatment temperature and composition of the medium and the treatment time, but also by controlling the electrical potential within the medium between a pair of electrodes in contact therewith. Preferably, for electrodes of specified composition and structure, this potential is maintained at a value between -600 mV and +300 mV.

Abstract: Glass bodies formed from a vitrifiable composition are given a desired coloration by introducing a reducing agent into surface layers of the body, during or after its formation from a molten composition, and the then the body surface into contact with a diffusion medium composed of a mixture of a salt furnishing reducible metal ions which are capable of being reduced by the reducing agent, and a diluting agent constituted by a salt of another metal, the body being subjected to temperature conditions such as to cause the reducible metal ions to diffuse into the body surface layers and to there be chemically reduced by the reducing agent.