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.

Laminated glass

The invention: Double sheets of glass separated by a thin layer of
plastic sandwiched between them.
The people behind the invention:
Edouard Benedictus (1879-1930), a French artist
Katherine Burr Blodgett (1898-1979), an American physicist
The Quest for Unbreakable Glass
People have been fascinated for centuries by the delicate transparency
of glass and the glitter of crystals. They have also been frustrated
by the brittleness and fragility of glass. When glass breaks, it
forms sharp pieces that can cut people severely. During the 1800’s
and early 1900’s, a number of people demonstrated ways to make
“unbreakable” glass. In 1855 in England, the first “unbreakable”
glass panes were made by embedding thin wires in the glass. The
embedded wire grid held the glass together when it was struck or
subjected to the intense heat of a fire.Wire glass is still used in windows
that must be fire resistant. The concept of embedding the wire
within a glass sheet so that the glass would not shatter was a predecessor
of the concept of laminated glass.
A series of inventors in Europe and the United States worked on
the idea of using a durable, transparent inner layer of plastic between
two sheets of glass to prevent the glass from shattering when it was
dropped or struck by an impact. In 1899, Charles E.Wade of Scranton,
Pennsylvania, obtained a patent for a kind of glass that had a sheet or
netting of mica fused within it to bind it. In 1902, Earnest E. G. Street
of Paris, France, proposed coating glass battery jars with pyroxylin
plastic (celluloid) so that they would hold together if they cracked. In
Swindon, England, in 1905, John Crewe Wood applied for a patent
for a material that would prevent automobile windshields from shattering
and injuring people when they broke. He proposed cementing
a sheet of material such as celluloid between two sheets of glass.
When the window was broken, the inner material would hold the
glass splinters together so that they would not cut anyone.Remembering a Fortuitous Fall
In his patent application, Edouard Benedictus described himself
as an artist and painter. He was also a poet, musician, and
philosopher who was descended from the philosopher Baruch
Benedictus Spinoza; he seemed an unlikely contributor to the
progress of glass manufacture. In 1903, Benedictus was cleaning his laboratory when he dropped a glass bottle that held a nitrocellulose
solution. The solvents, which had evaporated during the
years that the bottle had sat on a shelf, had left a strong celluloid
coating on the glass. When Benedictus picked up the bottle, he was
surprised to see that it had not shattered: It was starred, but all the
glass fragments had been held together by the internal celluloid
coating. He looked at the bottle closely, labeled it with the date
(November, 1903) and the height from which it had fallen, and put
it back on the shelf.
One day some years later (the date is uncertain), Benedictus became
aware of vehicular collisions in which two young women received
serious lacerations from broken glass. He wrote a poetic account
of a daydream he had while he was thinking intently about
the two women. He described a vision in which the faintly illuminated
bottle that had fallen some years before but had not shattered
appeared to float down to him from the shelf. He got up, went into
his laboratory, and began to work on an idea that originated with his
thoughts of the bottle that would not splinter.
Benedictus found the old bottle and devised a series of experiments
that he carried out until the next evening. By the time he had
finished, he had made the first sheet of Triplex glass, for which he
applied for a patent in 1909. He also founded the Société du Verre
Triplex (The Triplex Glass Society) in that year. In 1912, the Triplex
Safety Glass Company was established in England. The company
sold its products for military equipment in World War I, which began
two years later.
Triplex glass was the predecessor of laminated glass. Laminated
glass is composed of two or more sheets of glass with a thin
layer of plastic (usually polyvinyl butyral, although Benedictus
used pyroxylin) laminated between the glass sheets using pressure
and heat. The plastic layer will yield rather than rupture when subjected
to loads and stresses. This prevents the glass from shattering
into sharp pieces. Because of this property, laminated glass is also
known as “safety glass.”
Impact
Even after the protective value of laminated glass was known,the product was not widely used for some years. There were a number
of technical difficulties that had to be solved, such as the discoloring
of the plastic layer when it was exposed to sunlight; the relatively
high cost; and the cloudiness of the plastic layer, which
obscured vision—especially at night. Nevertheless, the expanding
automobile industry and the corresponding increase in the number
of accidents provided the impetus for improving the qualities and
manufacturing processes of laminated glass. In the early part of the
century, almost two-thirds of all injuries suffered in automobile accidents
involved broken glass.
Laminated glass is used in many applications in which safety is
important. It is typically used in all windows in cars, trucks, ships,
and aircraft. Thick sheets of bullet-resistant laminated glass are
used in banks, jewelry displays, and military installations. Thinner
sheets of laminated glass are used as security glass in museums, libraries,
and other areas where resistance to break-in attempts is
needed. Many buildings have large ceiling skylights that are made
of laminated glass; if the glass is damaged, it will not shatter, fall,
and hurt people below. Laminated glass is used in airports, hotels,
and apartments in noisy areas and in recording studios to reduce
the amount of noise that is transmitted. It is also used in safety goggles
and in viewing ports at industrial plants and test chambers.
Edouard Benedictus’s recollection of the bottle that fell but did not
shatter has thus helped make many situations in which glass is used
safer for everyone.