  Long-term corrosion of glass is studied using polarising light microscopy,
FTIR and SEM including EDX and elemental mapping. Early 19th century beads made
of lead-potassium glass are the object of the study. Non-uniformly distributed
internal stresses were introduced into the studied glass during bead
manufacturing. Corrosion of 19th century bead glass has been shown to comprise
several mutually connected processes developing in parallel and intensifying
one another. These processes are the depolymerization of glass, the directed
migration of alkali-metal impurities and local glass leaching, and the
nucleation of micro discontinuities followed by the formation of micro cracks
and their gradual growth. In course of time, their cumulative and apparently
synergistic effect results in glass fracturing terminated with bead crumbling
into tiny discoloured particles. All these phenomena are controlled by the
internal stress originated from the bead production process. Thus, the
phenomenon of stressed bead glass corrosion is the process of the internal
stress relaxation in glass through the nucleation and growth of cracks, which
lasts for many decades at room temperature. It is dramatically accelerated when
beads are heat treated. Annealing at 300{\deg}C for 15 min. is sufficient for
artificial ageing of initially intact beads. The corrosion has been observed to
occur in glass even if beads are kept in well-controlled museum environment.
The local thermal-fluctuation mechanism is proposed to account for the
corrosion phenomenon on an atomic scale. The approach based on the
thermal-fluctuation mechanism is applicable to describe degradation and
destruction processes in various solid substances and composite materials under
stress; this approach enables understanding the phenomena of formation and
degradation of nanostructures, e. g., heterostructures with quantum wells or
quantum dots.
