  Blue-green historical beads are sometimes referred to as instable ones
because of their degradability. At present, the cause of the phenomenon of
deterioration of the blue-green beads is unknown. We explore internal
microstucture of degrading blue-green historical beads and its evolution in the
process of bead deterioration. Investigating transmittance and scattering
spectra of visible and near infrared light we observe formation of microscopic
internal inhomogeneities with the sizes less than 150 nm in the glass bulk and
growth of their density with increase in degree of bead degradation. By means
of laser scanning microscopy we also observe numerous microinclusions and
microcracks on the cleavage surface of a partially degraded bead. We discuss
possible physical factors resulting in destruction of the blue-green beads.
