KSbOSiO4 microcrystallites as a source of corrosion of blue-green lead-potassium glass beads of the 19th century

Abstract

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 believe 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.

Glass depolymerization in the process of long-term corrosion: A study of deteriorating semiopaque turquoise glass beads using micro-FTIR spectroscopy

“…FTIR spectra of the turquoise glass seed beads at different stages of deterioration [13,15] are presented in figure 4. A strong and wide band in the region from 820 to 1250 cm −1 and weak bands in region from 650 to 820 cm −1 are observed in all spectra.…”

“…In the previous works, we established that formation of micro and nanocrystallites of orthorhombic KSbOSiO 4 (KSS) in glass matrix (figures 2(e)-(g)), which arise during glass melting and bubbling, 4 is one of the main causes of deteriorating of turquoise glass seed beads [7,8,15,14,16]. We concluded that KSS precipitates and their clusters gave rise to internal stress (likely, tension) causing strain (likely, tensile one) in the glass bulk.…”

“…We concluded that KSS precipitates and their clusters gave rise to internal stress (likely, tension) causing strain (likely, tensile one) in the glass bulk. In course of time, it leads to the conspicuous 'internal corrosion' of glass resulted from its slow fracturing and gradual formation of a network of cracks [7,8,15].…”

Raman microspectroscopy of blue‐green historical beads: Comparative study of undamaged and strongly degraded samples

“…). However, the results of the previous studies show the absence of sulfur and the presence of lead in similar beads.…”

“…The X‐ray fluorescence study of the 19th‐century cloudy blue‐green beads shows that the beads are made of lead–potassium glass, and light scattering spectroscopy demonstrates the presence of microscopic inhomogeneities on the cleavage surfaces of fragmented beads . Scanning electron microscopy, X‐ray energy‐dispersive spectroscopy microanalysis, and X‐ray diffractometry make it possible to identify inhomogeneities as orthorhombic KSbOSiO 4 (KSS) crystals . Such crystals often form relatively large clusters with sizes ranging from several hundreds of nanometers to several tens of micrometers.…”