Glasswork - the Scientia Review

Preservation
The breakdown of glass depends most directly upon
composition. Glass contains silica, alkali, and minute amounts of
calcium as primary constituents, and these ingredients each effect the
breakdown process Though glass is somewhat uniform in
composition, small differences in makeup account for large differences
in the breakdown process. Some types of Roman glass, for example,
are extremely resistant to breakdown, unlike much medieval glass
which degenerates with ease due to a high potash content; the potash
from beech wood renders the composition unstable.
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