Patent ID: 8196432

Claim:
A process for the continuous preparation of a composition comprising 10 to 70% SiO 2 , by weight, and 0.3 to 30% Na 2 O, by weight, in a furnace comprising at least two tanks in series, said process comprising introducing most of the silica (SiO 2 ) and at least one fluxing agent for the silica into a first tank comprising at least one submerged burner, melting most of the silica in the first tank, transferring the silica to a second tank comprising at least one submerged burner, and introducing into the second tank at least one powder selected from the group consisting of a thinner, a metal oxide, and mixtures thereof, wherein the metal oxide is selected from the group consisting of oxides of chromium, cobalt, copper, nickel, selenium, zirconium, titanium, manganese, praseodymium, iron, zinc and mixtures thereof, and wherein the first tank is heated to a higher temperature than the other tank(s) of the furnace, the temperature difference between the first tank and the other tank or tanks is at least 80° C., the first tank is heated to a temperature ranging from 1000 to 1350° C., and the other tank or tanks are heated to a temperature of at most 1150° C.