Why are flux blocks used in the molten-glass area of a furnace?

The term "flux blocks" in the context of glassmaking does not refer to a substance used to promote fluidity or remove impurities, as the term "flux" is defined in metallurgy. Instead, flux blocks are a specific type of refractory material used in the construction of glass-melting furnaces.12

In glass production, flux blocks are highly siliceous, dense firebricks specifically chosen for the portion of the furnace tank that comes into direct contact with molten glass. They are utilized in this area because they provide the necessary resistance to the corrosive environment created by the molten glass, helping to ensure the structural integrity and service life of the furnace. While other materials like mullite, fused alumina, and zirconia are also used for their chemical inertness and resistance to glass penetration, the term "flux block" specifically identifies these dense, siliceous bricks used in the melting tank.23