Sodium metaphosphate glasses containing chromium, manganese, cerium, copper, uranium, molybdenum, vanadium and titanium were equilibrated with air at different temperatures. The relative proportions of the oxidised and reduced forms were determined. Spectral absorption of glasses containing each of the above colouring constituents was measured and correlated with the ionic species present in the glass.A comparison of the redox equilibria in phosphate glasses with those in silicate and borate glasses showed that phosphate glasses exert a more reducing influence than silicate and borate glasses.