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GLASS FACT
GLASS IS
ACTUALLY DEFINED AS A LIQUID OF A VERY GREAT VISCOSITY
GLASS DEFINITION glass
[1] (noun) [Middle English glas, from Old English glaes; akin to Old
English geolu yellow -- more at YELLOW] First appeared before 12th
Century
1 : any of various amorphous materials formed from a melt by cooling
to rigidity without crystallization: as
a : a usu. transparent or translucent material consisting esp. of a
mixture of silicates
b : a material (as obsidian) produced by fast cooling of magma
GLASS FACT
Many people believe that glass
"flows" like a liquid, and the proof most often cited is that
stained glass windows in ancient cathedrals are thicker at the
bottom than at the top. The idea that glass is a highly viscous
liquid at room temperature has even made its way into some
textbooks.
Someone finally decided to test the
idea, and it turns out to be wrong. Edgar Dutra Zanotto, a professor
of materials engineering at the Federal University of Sao Carlos in
Brazil, looked up the chemical composition of some 350 pieces of
glass from 12th century cathedrals, calculated their viscosity, and
then determined their flow rates by extrapolating the viscosity
curves of hot glass to lower temperatures.
According to Zanotto's
calculations, you would have to heat a typical 12th-century piece of
glass to approximately 414 degrees C to observe any significant
movement in the course of 800 years. Without high heat, you would
have to wait about a hundred million trillion trillion years to
observe any flow, far longer than the age of the universe.
GLASS FACT
FOURTH STATE OF MATTER
What
makes glass a unique material is that it's always a liquid; glass is
known as "the fourth state of matter" because it has no solid or
gaseous state. Even though windows and wine goblets seem to be
solid, the glass they're made of is actually a super-cooled liquid
whose molecules are moving very, very slowly. As the glass heats up
in the kiln, its liquid nature becomes visible. At about 1450oF, you
can see the edges of the cut glass starting to soften and melt. At
1550oF, most glass is beginning to actually flow and behaves like
syrup (extremely hot syrup!), and as its temperature continues to
rise, you can actually see it moving in the kiln.
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