Origin of Na2SO4 blisters in sheet glass

The properties and origin of fine Na 2 SO 4 blisters have been studied experimentally. They are 0.1–1.0 mm in size and contain crystalline Na 2 SO 4 with a small amount of CaO and K 2 O. Most of them are formed in molten glass during decomposition of the batch mixture. The blisters are formed by condensation of Na 2 SO 4 from Na 2 O and SO 3 selectively absorbed into dolomite at an early stage of batch melting. They remain immiscibly in molten glass, after MgO and CaO in the dolomite have been dissolved into the glass.