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.