The first mentions of glass production in Tuscany dates back to about the
6th century dc (Florence, Piazza della Signoria).
As of the 13th century, glass production began to develop, especially in the
Gambassi and Montaione areas, making Valdelsa one of the most important
areas for the production of glass in the whole peninsula.
These two centres gave birth to generations of glassmakers, who opened
furnaces in many Italian towns and sometimes even abroad.
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Historic and archaeological research carried out over the last twenty years
has shed light on over twenty glass production sites located in Valdelsa,
operational between the 13th and 18th centuries, in which numerous rejects,
crucibles, waste and parts of factory walls have been found.
The study of these finds has made it possible to glean important information
on the technologies used in medieval production.
The furnaces were round or rectangular and were fuelled by
wood.
They could hold up to four crucibles, which were accessed by pontils through
the same number of openings in the furnace wall; the highest part contained
the tempering colour, separated from the combustion chamber by a dividing
floor.
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The process began with the melting of the raw materials, which were then
refined, followed by free or moulded blowing and tempering.
Due to the presence of impurities, the glass produced often took on a more
or less greenish hue, but objects were also made from blue and
amber-coloured glass.
During the Middle Ages the various processes were perfected, production
plants became more specialised and the objects produced became clearer and
clearer.
