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 within the molten metal at least a trace of an element with which an impurity in the metal preferentially reacts. Preferably a ribbon of glass is supported on a bath of molten tin or tin alloy covered by a plenum of a protective atmosphere. There is incorporated in the molten metal a trace of an element selected from lithium, sodium, potassium, magnesium, calcium, barium, aluminium, indium, titanium, vanadium, chromium, manganese, iron, zinc, zirconium, niobium, carbon and silicon. Preferably a concentration of 50 p.p.m. of sodium as a sodium/tin alloy or 10 p.p.m. of magnesium of a magnesium/tin alloy is used and is sufficient to ensure that any impurity such as oxygen and/or sulphur always reacts, and also forms a means for controlling migration of tin into the underface of the glass ribbon. The titanium, vanadium, chromium, niobium, zirconium or silicon, which are insoluble in the bath, may be used as grids immersed in the bath, the oxygen or sulphur reaction product forming on the grid, which may be removed and cleaned. A ribbon of glass formed in this way has a "fire-finished" quality.