A Clear View: History of Automotive Safety Glass
By Llewellyn Hedgbeth
Early cars were little more than motorized buckboards but it didn't take long for drivers to determine they'd like a little protection from road hazards like sharp flying rocks. In 1904 when the first windshields were introduced, most were a horizontally-divided piece of plate glass just like the glass used for house windows. When the top half got too dirty to see through, a driver could fold it down and keep going. Ford, in 1908, advertised its Model T for $850 — unless a driver also wanted fancy extras like a windshield, speedometer, and headlights, equipment that boosted the price another $100. Likewise, in 1913 Reo offered a windshield as optional equipment. In 1915, though, Oldsmobile was first to sell the top and windshield as standard equipment.
As more and more cars took to the roads, a rise in accidents was inevitable. When one of these early cars was involved in an accident, it was not uncommon for the driver at a minimum to be injured by flying shards of glass or, far worse, lose his life after going headfirst through the windshield. The latter event was known as wearing a glass necklace. In the teens motorists filed a number of lawsuits against car manufacturers, asserting the car makers were the cause of their windshield-related injuries.
There are also stories that Henry Ford and some of his closest friends were themselves injured by flying glass in accidents. Whatever the circumstances — whether personal experience with accidents, discussions with attorneys about liability issues, etc., Ford was finally convinced it was time to make car windshields safer. Another impetus for his decision may have been one reported on by author Ford R. Bryan in his 1993 book "Henry's Lieutenants": In 1918 Henry Ford saw distortion in the rear window of a Model T and decided he needed to produce improved glass. He also, however, needed less expensive glass. With more and more customers opting for enclosed vehicles, glass was harder to come by and the price of glass had risen nearly three-fold. Clarence Avery, a Ford employee, began working with Pilkington Co., a British glass manufacturer, on a new glass-making process. By the end of 1919 they had perfected a process for pouring molten glass through rollers and onto a mobile table. The table then carried the glass under several grinders and polisher until the product was finished. At Ford's extensive River Rouge Plant there was a steel mill, glass factory, and car assembly line. At least initially Ford manufactured the glass it needed. In late 1919 Ford began using laminated glass, over the next decade directing its use in all Ford cars.
Two European inventors developed glass laminating, Frenchman Edouard Benedictus and Briton John C. Wood. Benedictus, an accomplished artist, writer, composer, book binder, fabric designer, and scientist, made an accidental discovery in his lab. As the story goes, one day in 1903 he dropped a beaker and his lab assistant, thinking it clean, put it back on the shelf. Later as Benedictus climbed a ladder, he bumped that shelf, once again sending the flask to the floor. It broke — but its pieces held together. Cellulose nitrate, a clear liquid plastic left in the beaker, had dried and kept the glass from breaking into shards. After experimenting further Benedictus developed safety glass, two layers of plate glass with a layer of cellulose between them, and he hoped to promote its use in automobiles. Unfortunately, it was costly and both manufacturers and drivers had a strong interest in keeping cars affordable. Though Benedictus was granted a patent in 1909, the product was not put into use until World War I when laminated glass was used in the goggles of gas masks. Meanwhile Wood had also been working with cellulose and devised another method for adding a protective layer (originally tree resin, later cellulose) between two pieces of glass and creating shatter-resistant glass. His method was patented in 1905. Benedictus, in 1910, added a gelatin layer which stuck to both panes of glass and patented Triplex. The Triplex Glass Company was founded in 1923 and Triplex glass was brought to the U.S. in the twenties.
Also about this time a new urethane glue was also used to bond the glass to the frame. The laminated window was more secure and if it broke it broke in a spider's web pattern rather than splintering into small shards. Because it was difficult to penetrate, it also kept passengers from being ejected. Its strength actually meant more structural integrity for the car if it rolled over. There were two significant problems with the laminated glass, however: its inner celluloid layer would discolor, darken, and become brittle over time and it could be punctured easily. In 1938 Carleton Ellis patented a glass-clear synthetic resin that did not discolor over time. Beginning in the late thirties then, manufacturers began using instead Polyvinyl Butyral (PVB) which made laminated glass clearer and stronger and helped block high frequency sound and harmful UV rays.
Throughout the twenties there were a number of changes in windshield production. In 1924 some local police departments were the beneficiaries of one windshield development. Lincoln touring sedans called Police Flyers came specially equipped with bullet-proof (glass and polycarbonate) windshields nearly an inch thick. The Bonnie and Clyde era was still some years off, but these windshields were early preparation for the good guys. In 1926 Rickenbacker offered safety glass as a standard feature all the way around its car. As Ford continued utilizing safety glass, a 1928 full-page ad for the Triplex Safety Glass Company touted, "The new Ford is equipped with a windshield of Triplex — the glass that will not shatter." Other manufacturers followed suit. Pittsburgh Plate Glass (the first financially successful U.S. plate glass manufacturer) in 1928 introduced Duplate, its economical version of laminated glass.
Changes to the windshield continued in the thirties, as well. In 1930 Cadillacs came with a vertically split-"V" type swing-out windshield. The sides of the front windshield joined in a point at the center of the hood. Now in the Smithsonian's collection is an early windshield defroster manufactured about 1930 by an Illinois company. Attached to the windshield with suction cups, the plug-in Sinko Windshield Heater would defog windows. Also in 1930 Chevrolet's AD Universal had a slightly sloped windshield and 1932 Chevrolets came with a tiltable windshield. A 1933 Libbey-Owens-Ford (sole suppliers of glass to GM) ad alerted customers that for only $1.50 more on their monthly car payment they could have safety glass that provided the greatest available protection against flying glass. Then in 1934 the Chrysler Imperial Airflow CW appeared, the first production car to come with a single-piece curved windshield. In 1936 the vertically split windshield was introduced on GM cars.
Trouble came to automotive glass when in December 1936 the Federation of Flat Glass Workers demanded more pay and a closed union shop. When their demands were not met, roughly 13,000 strikers brought plate glass manufacturing to its knees. At that time Pittsburgh Plate Glass and Libbey-Owens-Ford together made 85% of car safety glass. Ford prepared to make the glass it needed to continue production and GM reported they had a month's supply. Nonetheless, before the strike was settled (in part due to Walter Chrysler's intervention) there had been thousands of lay offs in Ford and Pierce-Arrow plants.
With the strike settled and production resumed, in 1937 the use of safety glass was finally mandated for all car models. In 1939 Libbey-Owens-Ford was advertising a new safety plate glass that was stronger, safer, and more flexible. Then standard equipment on many models, it was said to have no distortion and to be "safer because it's laminated — clearer because it's plate". That ad also relied on what now might appear as shaky science. It claimed that Dr. A. H. Ryan, a nationally known physiologist, tested safety plate glass over safety sheet glass with the following results: Passengers in moving vehicles with safety sheet glass (rather than window-like safety plate glass) had 62% greater eye fatigue, 140% more headaches, 17% greater frequency of tiredness and sleepiness, 40% greater increase in blinking, 82.2% decrease in judgment of distances, and 17% loss in ability to read road signs. (Hey, who would argue with those figures?)
In 1938 Pittsburgh Plate Glass came out with Herculite, tempered glass that was considerably more shatter resistant than plate glass. Tempered glass is made by placing glass into an atmospheric oven which heats and hardens it. Rapidly cooled after its formation, it develops an even tougher outer skin. Its strength exceeds that of regular glass by five to ten times. Nonetheless it retains its flexibility and can be cut and formed into many shapes. It can withstand great force and if it is broken it breaks into relatively small smooth cubical pebbles. Besides all those positive attributes, it is thinner than laminated glass and considerably cheaper to fabricate.
The forties brought even further progress for automotive windshields. In 1947 Studebaker introduced its Starlight coupe with a curved windshield. Far more striking, the avant garde 1948 Tucker automobile came with "Pop-Out" windshields. Libbey-Owens-Ford manufactured them. A Tucker sales brochure explained that the "laminated safety glass [was] mounted in sponge rubber fastening so that a hard blow from within will eject it in one piece." It was also that year that Buick, Oldsmobile, and Cadillac added compound-curved windshields to their cars.
From 1936 to 1959 safety glass was used in all save the rear window of cars. In the late 1950s, though, car manufacturers were looking for a cheaper option and began using tempered glass for side and rear windows. Besides saving on cost, tempered glass made it easier for rescuers to cut into a vehicle to free trapped passengers. Some argue, however, that tempered glass should not be used on side windows since tempered glass windows will not prevent partial ejection in side collisions or rollovers. Another disadvantage with tempered glass is that it cannot be repaired as laminated glass can.
There were also styling innovations in the fifties. GM's LeSabre boasted the first wraparound, panoramic windshield designed to reduce the driver's blind spot. Its 1953 limited edition Cadillac Eldorado also offered the wraparound windshield. By 1957 most cars had curved windshields — at the top and bottom and also at the sides. With curved side windows automotive stylists could add more interior room and they could produce a smoother body line. Engineers developed techniques to drill holes in side windows for anchoring mechanisms resulting in further safety improvements. As the amount of glass increased, drivers were aware of less privacy and greater solar buildup, so tinted windshields were made available. Glass manufacturers added iron oxide to glass giving it a blue or blue-green color. They could also add a darker band of color at the top of the windshield by applying a dye to the PVB inner layer. Each state regulates how much tint can be applied to windows.
Glass production suddenly became cheaper in 1959 with the Pilkington development of the float process which significantly improved both quality and clarity of glass. In the float method raw materials are combined and melted in a tank where they are further mixed to ensure homogeneity and to remove CO 2 bubbles. The refined molten glass is then forced through a small opening onto a layer of molten tin. Because the glass is lighter than the tin, the glass floats — like oil on water. When the glass is cooled, lift-out rollers remove it from the tin bed so it can slowly be cooled further. With this method there is no need for later polishing and grinding. Roughly a quarter of all float glass produced goes into car manufacturing.
The public became more interested in automotive safety features in the 60s, fueled in part by consumer protectionist Ralph Nader who campaigned for government safety standards. Beginning in 1966 cars came equipped with improved laminated windshields that could withstand nearly three times the impact of earlier versions. In the 60s and 70s Federal Motor Vehicle Safety standards were set for the strength and clarity of laminated windshields (FMVSS 205); windshield retention strength during accidents (FMVSS 212); roof rigidity in rollover accidents (FMVSS 216); and limits on windshield penetration (FMVSS 219). In addition, the National Highway Traffic Safety Administration (NHTSA) was formed.
Nowadays windshields continue to grow in complexity and sophistication. Windshields are larger and often more raked. Some provide increased visibility with a windshield that extends up into the roof above the driver or one that wraps into the side of the car. Modern windshields can filter 95-99% of UV rays. Since the 90s a hybrid film with dye to absorb heat and metal to ban sun rays has provided significant reduction in infrared (IR) rays and consequent internal heat gain.
Nano-technologies are clearly the wave of the future, though. Window film with ceramic or crystalline particles can block the IR portion of the solar spectrum. We already have "smart glass" with particles held in liquid suspension that can control the amount of heat and light transmitted through the windshield. GM is working with Carnegie-Mellon and USC on a Heads-Up Display utilizing a sensor-laden windshield to provide data to the driver. In dense fog, for instance, lasers would provide information as to the road's edge. We may soon see cars with sensors that project data onto the windshield, perhaps eliminating the need for a speedometer. While cost is still prohibitive for such applications, prices will no doubt drop as further technical improvements are made. There are even predictions that the Geyser windshields that clean themselves with nano-dust particles (now being tested in Italy on the Hidra) may be more widely available within the next five years. That could mean eliminating windshield wipers altogether. Look out, Jetsons; here we come!