Effect Of Network Modifiers On The Opalescence And Crystallisation Behaviour Of Opal Glasses

This paper reports on the phase separation, crystallisation and opalescence of a series of the aluminophosphosilicate glasses by substitution of one type of network modifying oxide for another. Using x-ray diffraction, it was found that the NaCaPO4 crystals are present in all quenched glasses, which greatly enhances the opalescence effect. The glasses remain transparent when Na2O and CaO are present, whereas they become opalescent when Li2O and MgO are partially substituted for Na2O and CaO respectively.