The Role of Tin in Copper Ruby Glass—Viscosity Measurements

Abstract

A new mechanism for striking of colour in copper ruby glass was recently suggested: 2 Cu-O-Si≡ (chilled glass) striking → Cu2O (red colourant) −+≡Si-O-Si≡. It does not need tin, considered essential as per the earlier mechanism. The actual role of tin has therefore been investigated. A copper ruby glass melted without tin became amber indicating the presence of Cuo. For confirmation, its low temperature viscosity has been studied. Viscosity of chilled glass remains unchanged on annealing. This indicates presence of Cuo in chilled glass rather than of Cu+ which, on annealing, would have increased the viscosity several fold due to formation of bigger structural linkages. Hence in absence of tin the reduction of Cu+ to Cuo is almost instantaneous in the melt and the latter makes the glass amber. Cu+ being absent, formation of Cu2O (red colourant) is not possible on striking. But when tin is used, availability of Cu+ is prolonged. It is likely that tin acts as a protector for Cu+ in molten glass. Probably rea...