A study of the criteria required to manufacture multicomponent semi-transparent silicate glasses, so called "alabaster" glasses, has found that the optical effect is caused by noncrystalline potassium sulfate droplets. The droplets were characterised by use of XRD, SEM/EDX and Raman spectroscopy. The size range of the particles is of the order of 5-50 micrometers. It was found that the droplets consisted of potassium sulfate, even if other sulfate compounds were added to the glass. The amount of sulfate compound added, the melting temperature of the furnace and the melting time have significant effects on the optical density of the glass. The optical density of the glass can be correlated to the calculated surface tension of the host glass, suggesting that phase separation of a sulfate enriched liquid phase is part of the mechanism.
