Process for making glass with agglomerated refining agents

Claim 1

In the process for making glass in which a refining agent comprising a mixture of metal sulfates and reducing agents is dispersed uniformly throughout the vitrifiable charge of glassmaking raw materials prior to melting the charge, and in which the vitrifiable charge is heated to melt the charge and to cause the refining agent to evolve gases which enlarge bubbles of other gasses and remove them from the molten glass as the bubbles rise upwardly in the molten glass to escape therefrom at the upper surface thereof; the improvement which comprises employing as the refining agent finely-divided particles of metal sulfate and a reducing agent having a particle size of less than about 0.1 mm, the finely-divided particles of metal sulfate and reducing agent being intimately mixed together and formed into agglomerates at least 10 times greater in size than the average particle size of their constituent materials, and wherein the relative amounts of reducing agent and metal sulfate in the agglomerates is such that the reducing agent can reduce at least one-fourth of the sulfate ions (SO 4 = ) to the state of sulfide ions (S = ), and wherein the amount of refining agent added to the vitrifiable charge of glassmaking raw materials is such that the amount of created sulfide, expressed as SO 3 , is at least 0.05% by weight of the glass to be obtained.