Today, we learn to make window panes. The
University of Houston's College of Engineering
presents this series about the machines that make
our civilization run, and the people whose
ingenuity created them.
We've made glass in many
forms for about 4500 years. But two features of
glassmaking are surprising. First, glassmaking
processes have been far harder to invent than we
imagine. The second surprise is that artisans could
make really fine glass tableware long before they
could make a good windowpane.
The ancient Egyptians and Greeks made crude glass
decorations. But today's basic soda-lime glass --
made of sand, limestone, and sodium carbonate -- is
far more recent. The first glass of any real
quality was made in Hellenistic North Africa around
300 BC. Soda-lime glass came quickly on its heels.
Both Hellenistic artisans and the Romans who
followed them made fine glass tableware. Tableware
remained the most common glass product for a long
The stained glass art
of the Gothic cathedral was so highly developed
that we might think glass handling had reached high
perfection at that point. Actually, what had
reached a perfection that seems to be beyond our
reach today was coloring the glass. A medieval
window admitted light, but it was seldom smooth
enough to provide a clear view. Cathedral windows
did not even try to offer any view of the outside
world. What they did so beautifully was to offer
illuminated bible stories to the faithful who, for
the most part, didn't read.
Medieval glassblowers made two kinds of flat glass
sheets. One technique was to blow a large cylinder.
They then cut the cylinder open and flattened it
out while it was still hot. The other flat glass
sheet was called crown glass. They made it by
spinning molten glass and letting centrifugal forces spread it from a
central point. Crown glass was the most common flat
glass for a long time. It underwent considerable
refinement. But, even as late as 1800, most
domestic windows still displayed a characteristic
umbilical imperfection called a crown at their
The French developed the superior plate glass
process in the latter 18th century. First a plate glass is poured out in a mold. Then the glass needs
expensive grinding and polishing.
To provide common people -- you and me -- with good
domestic windowpanes required a continuous
mechanized process. Molten glass had to be rolled
out in smooth continuous sheets. That couldn't be
done until we had modern process machinery. It was
in the early 1800s that the first inexpensive
rolled window glass became available. That was
little over a century and a half ago.
The lowly windowpane reminds us how we take
yesterday's great acts of inventive genius for
granted. Windowpanes are the result of terribly
complex high-temperature chemical and mechanical
processes. Yet few things give our daily lives the
soul-settling grace of these unobtrusive bridges to
the outer world -- this technology which is at its
best when it is completely invisible.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds