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Glass corrosion is a crucial problem in keeping and conservation of beadworksin museums. All kinds of glass beads undergo deterioration but blue-greenlead-potassium glass beads of the 19th century are subjected to the destructionto the greatest extent. Blue-green lead-potassium glass beads of the 19thcentury obtained from exhibits kept in Russian museums were studied with thepurpose to determine the causes of the observed phenomenon. For the comparison,yellow lead beads of the 19th century were also explored. Both kinds of beadscontain Sb but yellow ones are stable. Using scanning electron microscopy,energy dispersive X-ray microspectrometry, electron backscatter diffraction,transmission electron microscopy and X-ray powder analysis, we have registeredthe presence of crystallites of orthorhombic KSbOSiO$_4$ and cubicPb$_2$Sb$_{1.5}$Fe$_{0.5}$O$_{6.5}$ in glass matrix of blue-green and yellowbeads, respectively. Both compounds form at rather high temperatures obviouslyduring glass melting and/or melt cooling. We suppose that the crystallitesgenerate internal tensile strain in glass during its cooling which causesformation of multiple microcracks in inner domains of blue-green beads. Wesuggest that the deterioration degree depends on quantity of the precipitates,their sizes and their temperature coefficients of linear expansion. Inblue-green beads, the crystallites are distributed in their sizes from$\sim\,$200 nm to several tens of $\mu$m and tend to gather in large colonies.The sizes of crystallites in yellow beads are several hundreds of nm and theirclusters contain few crystallites. This explains the difference in corrosion ofthese kinds of beads containing crystals of Sb compounds.

Crystallites in Color Glass Beads of the 19th Century and Their Influence on Fatal Deterioration of Glass