A QUÍMICA DOS VITRAIS

THE CHEMISTRY OF THINGS
Today we will show you how well chemistry connects with art and beauty.
Who has never felt overwhelmed by the light and colour of stained glass?
The use of stained glass to embellish basilicas and cathedrals
has occurred since the early Middle Ages
but the origin of coloured glass is much earlier
as the Egyptians and Romans were already experts producers.
The chemistry of stained glass is intertwined with the chemistry of actual glass.
Glass is obtained from the fusion of silicon dioxide sand or silica.
Silica is a crystalline solid, i.e. a solid with regular and repetitive packaging of its atoms
which in this case, are arranged in pyramids
containing a silicon atom surrounded by four oxygen atoms.
Glass is formed by cooling the fused silica
under conditions which do not allow it to recover this regular packing
resulting in an irregular and non-repetitive arrangement, i.e., an amorphous solid.
Of course, glass is also a chemical recipe!
Common glass is a mixture of silica, sodium carbonate and calcium oxide
with smaller portions of aluminum oxide, sodium chloride and other salts
each with their own role:
"network formers"
"network modifiers"
"melting agents"
For stained glass it is important to highlight the role of the "melting agents"
Melting agents are substances added to silica to reduce its melting point.
In fact, the melting point of pure silica is about 1700 ° Celsius
a temperature very difficult to achieve
even more so when ovens used wood as fuel.
Therefore, the first glass producers used "melting agents " as plant ash and sodium carbonate.
These materials contained several impurities
and coloured glasses resulted from these impurities.
The first craftsmen could not control the colour of the glass they produced
but when they began to understand the origin of colour, there was a true explosion of experiments
to discover the most suitable substances to get each specific colour.
It was a search involving artisans and alchemists
which had many aspects of real scientific chemical research!
And now, do you believe it was chemistry that brought us the beauty of stained glass?
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