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.