Nano and microcrystallites of KSbOSiO₄ in glass matrix as a source of internal strain and fatal corrosion of historic turquoise glass

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

“…Orthorhombic KSS microcrystals could have been formed during glass melting and bubbling. [23] Similar spectra have been obtained for blue-green African beads in Prinsloo et al, [25] where a developed narrowband centered at 533 cm −1 is assigned to lazurite. The inset to Figure 2 shows the Raman spectrum of lazurite (mineral sample) measured at an excitation wavelength of 532 nm.…”

“…Thus, we may conclude that antimony‐containing substances had been used as opacifiers in the fabrication of beads. Orthorhombic KSS microcrystals could have been formed during glass melting and bubbling …”

“…Microphotographs (polarized light) of (a) undamaged and (b) strongly degraded beads and scanning electron microscope images of a strongly degraded bead obtained using (c) secondary and (d) backscattered electrons. Clusters of potassium antimony silicate microcrystals are seen in the right‐hand image as white fragments [Colour figure can be viewed at wileyonlinelibrary.com]…”

“…Such crystals often form relatively large clusters with sizes ranging from several hundreds of nanometers to several tens of micrometers. KSS precipitates and their clusters give rise to internal glass corrosion of the Sb‐rich lead–potassium turquoise glass . Potassium and antimony may form KSS crystallites during glass melting, bubbling, and melt cooling.…”

“…KSS precipitates and their clusters give rise to internal glass corrosion of the Sb-rich lead-potassium turquoise glass. [23] Potassium and antimony may form KSS crystallites during glass melting, bubbling, and melt cooling. Tensile strain arising in the glass matrix in the course of cooling due to difference in linear expansion coefficients of glass and crystals causes glass cracking and, eventually, its fragmentation to sand grains.…”