Page 32 - Between light and shade

between light and shade, TRANSPARENCy and reflection

narrow steel window frames, characterises the
modernist movement.

Drawn crystal clear glass was produced on
an industrial scale from 1903 10. Drawing leaves
raised lines on the glass, which was unobtru-
sive but characteristic. This physical property of
transparency and the resulting faint reflections
represented both strengths and weaknesses. It
could be polished to produce perfectly flat panes
and used for double glazing (from 1912 in the
United States), but was gradually superseded
by so-called “float” glass 11 from 1952 onwards.
Manufacture of the latter uses less energy and
allows very large panes to be produced. Some
glassmakers, such as AGC Interpane in Germany,
are now able to produce panes of glass measuring
3 m wide, 18 m long and 20 mm thick! However,
the first generation of float glass had an emerald
green tint, which was more pronounced the
thicker it was, reducing light transmission 12 and,
imperceptibly but genuinely, impairing colour
perception 13. What is more, this glass could be

10 Drawn glass was invented in Charleroi by the Belgian engineer
Emile Fourcault, with the French-Belgian Emile Gobbe, who
filed his first patent in 1901.
11 Float glass was invented by the English engineer Sir Alastair

Pilkington, who filed his first patent in 1952.
12 Glazing is also characterised by its light transmission (LT). This
means that 6 mm to 12 mm thick extra-clear float glass has an LT
of 91% compared to an LT of 87% − 88% for ordinary float glass.
13 Colour perception is measured by the color rendering index
(CRI), a figure between 1 and 100, which represents the degree

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