Improvements in or relating to the manufacture of flat glass

In the manufacture of flat glass during which the glass is in contact with molten metal, there is maintained in the molten metal at least a trace of an element with which an impurity in the molten metal preferentially reacts to form a product at least a part of which is dissolved in the underface of the glass. Preferably a ribbon of glass is supported on a bath of molten tin, or tin alloy, over which there is a plenum of a protective atmosphere, and a trace of at least one element selected from the group lithium, sodium, potassium, magnesium, calcium, barium, indium, iron and zinc is maintained in at least one region of the bath so that an impurity such as oxygen and/or sulphur reacts preferentially with this element, the reaction product so formed being dissolved in the underside of the glass without damaging said underface. As examples 5 parts per million of magnesium, or 250 parts per million of zinc, are given as concentrates of the element in the bath.