The surface of flat glass are separately contacted with the bodies of molten, electrically conductive material, and a controlled electric current is passed through the glass between these isolated bodies to produce a predetermined modification of the surface constitution of the glass. During the float process, for example, an electric current may be passed through the glass between the bath of molten tin or tin alloy on which the glass advances, and a pool of molten metal, e.g. tin, lead, or bismuth or alloys of these, confined on the upper surface of the glass. A two-stage treatment of the glass can be effected by passing currents between the surface of the molten metal bath and each of two electrically isolated pools of molten metal on the upper surface of the glass.
