Presently, deterioration of glass beads is a significant problem in conservation and restoration of beaded exhibits in museums. Glass corrosion affects nearly all kinds of beads but cloudy blue-green ones are more than others subjected to disastrous destruction. However, physical and chemical mechanisms of this phenomenon have not been understood thus far. This article presents results of a study of elemental and phase composition of glass of the blue-green beads of the 19th century obtained from exhibits kept in Russian museums. Using scanning electron microscopy, X-ray microanalysis, and X-ray powder analysis, we have detected and investigated Sb-rich microinclusions in the glass matrix of these beads and found them to be micro crystallites of KSbSiO5. These crystallites were not detected in other kinds of beads which are much less subjected to corrosion than the blue-green ones and deteriorate in a different way. We believe that individual precipitates of KSbSiO5 and especially their clusters play a major role in the blue-green bead deterioration giving rise to slow internal corrosion of the bead glass.
It is known from archeology and history of arts, however, that beads have been used for adornment, especially for ornamentation of clothes or decorative weaving, during the whole human history since the very ancient time.2
A higher temperature of the phase transition between tetragonal and orthorhombic phases of KSbOSiO4 (1200 °C) is given in Ref. 31.