Pyrex glass

The invention: Asuperhard and durable glass product with widespread
uses in industry and home products.
The people behind the invention:
Jesse T. Littleton (1888-1966), the chief physicist of Corning
Glass Works’ research department
Eugene G. Sullivan (1872-1962), the founder of Corning’s
research laboratories
William C. Taylor (1886-1958), an assistant to Sullivan
Cooperating with Science
By the twentieth century, Corning GlassWorks had a reputation
as a corporation that cooperated with the world of science to improve
existing products and develop new ones. In the 1870’s, the
company had hired university scientists to advise on improving the
optical quality of glasses, an early example of today’s common practice
of academics consulting for industry.
When Eugene G. Sullivan established Corning’s research laboratory
in 1908 (the first of its kind devoted to glass research), the task
that he undertook withWilliam C. Taylor was that of making a heatresistant
glass for railroad lantern lenses. The problem was that ordinary
flint glass (the kind in bottles and windows, made by melting
together silica sand, soda, and lime) has a fairly high thermal expansion,
but a poor heat conductivity. The glass thus expands
unevenly when exposed to heat. This condition can cause the glass
to break, sometimes violently. Colored lenses for oil or gas railroad
signal lanterns sometimes shattered if they were heated too much
by the flame that produced the light and were then sprayed by rain
or wet snow. This changed a red “stop” light to a clear “proceed”
signal and caused many accidents or near misses in railroading in
the late nineteenth century.

Two solutions were possible: to improve the thermal conductivity
or reduce the thermal expansion. The first is what metals do:
When exposed to heat, most metals have an expansion much greater  
than that of glass, but they conduct heat so quickly that they expand
nearly equally throughout and seldom lose structural integrity from
uneven expansion. Glass, however, is an inherently poor heat conductor,
so this approach was not possible.
Therefore, a formulation had to be found that had little or no
thermal expansivity. Pure silica (one example is quartz) fits this description,
but it is expensive and, with its high melting point, very
difficult to work.
The formulation that Sullivan and Taylor devised was a borosilicate
glass—essentially a soda-lime glass with the lime replaced by
borax, with a small amount of alumina added. This gave the low thermal
expansion needed for signal lenses. It also turned out to have
good acid-resistance, which led to its being used for the battery jars
required for railway telegraph systems and other applications. The
glass was marketed as “Nonex” (for “nonexpansion glass”).
From the Railroad to the Kitchen
Jesse T. Littleton joined Corning’s research laboratory in 1913.
The company had a very successful lens and battery jar material,
but no one had even considered it for cooking or other heat-transfer
applications, because the prevailing opinion was that glass absorbed
and conducted heat poorly. This meant that, in glass pans,
cakes, pies, and the like would cook on the top, where they were exposed
to hot air, but would remain cold and wet (or at least undercooked)
next to the glass surface. As a physicist, Littleton knew that
glass absorbed radiant energy very well. He thought that the heatconduction
problem could be solved by using the glass vessel itself
to absorb and distribute heat. Glass also had a significant advantage
over metal in baking. Metal bakeware mostly reflects radiant energy
to the walls of the oven, where it is lost ultimately to the surroundings.
Glass would absorb this radiation energy and conduct it evenly to
the cake or pie, giving a better result than that of the metal bakeware.
Moreover, glass would not absorb and carry over flavors from
one baking effort to the next, as some metals do.
Littleton took a cut-off battery jar home and asked his wife to
bake a cake in it. He took it to the laboratory the next day, handing
pieces around and not disclosing the method of baking until all had
agreed that the results were excellent. With this agreement, he was
able to commit laboratory time to developing variations on the
Nonex formula that were more suitable for cooking. The result was
Pyrex, patented and trademarked in May of 1915.
Impact
In the 1930’s, Pyrex “Flameware” was introduced, with a new
glass formulation that could resist the increased heat of stovetop
cooking. In the half century since Flameware was introduced,
Corning went on to produce a variety of other products and materials:
tableware in tempered opal glass; cookware in Pyroceram, a
glass product that during heat treatment gained such mechanical
strength as to be virtually unbreakable; even hot plates and stoves
topped with Pyroceram.
In the same year that Pyrex was marketed for cooking, it was
also introduced for laboratory apparatus. Laboratory glassware
had been coming from Germany at the beginning of the twentieth
century; World War I cut off the supply. Corning filled the gap
with Pyrex beakers, flasks, and other items. The delicate blownglass
equipment that came from Germany was completely displaced
by the more rugged and heat-resistant machine-made Pyrex
ware.
Any number of operations are possible with Pyrex that cannot
be performed safely in flint glass: Test tubes can be thrust directly
into burner flames, with no preliminary warming; beakers and
flasks can be heated on hot plates; and materials that dissolve
when exposed to heat can be made into solutions directly in Pyrex
storage bottles, a process that cannot be performed in regular
glass. The list of such applications is almost endless.
Pyrex has also proved to be the material of choice for lenses in
the great reflector telescopes, beginning in 1934 with that at Mount
Palomar. By its nature, astronomical observation must be done
with the scope open to the weather. This means that the mirror
must not change shape with temperature variations, which rules
out metal mirrors. Silvered (or aluminized) Pyrex serves very well,
and Corning has developed great expertise in casting and machining
Pyrex blanks for mirrors of all sizes.