KSbOSiO$_4$ microcrystallites as a source of corrosion of blue-green   lead-potassium glass beads of the 19th century
  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 KSbSiO$_5$. 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 belive that individual precipitates of KSbSiO$_5$ and especially their clusters play a major role in the blue-green bead deterioration giving rise to slow internal corrosion of the bead glass. 
T. V. Yuryeva, I. B. Afanasyev, E. A. Morozova, I. F. Kadikova, V. S.   Popov, and V. A. Yuryev
cond-mat.mtrl-sci