Pain in the GlassMay 01, 2021 01:48PM ● By Gayle Morrow
“Damn. A crack.” I never heard the stone that hit the windshield, never saw the tiny chip that started the thing, but there it was, clear as a curse, beginning low, about halfway along the length of the driver’s side wiper blade, then, almost before my eyes, meandering like a river across the bottom of the windshield, taking a bit of a jog up, then turning back down low again to a random, and, I hope, permanent, terminus near to where the glass meets the body of the car. All in all, about two feet of something that could cost me a lot of money. I was not impressed. Glass. To put it in really scientific terms, glass is pretty amazing stuff. Watching the seemingly arbitrary path of this crack got me wondering whether glass has a grain, you know, like wood does. As near as I can figure, the answer is no.
Wood, of course, is, or was, a living thing consisting of living cells. Wood’s grain comes from the alignment of its long cells with the trunk, limbs, and roots. There’s some order there.
According to folks who know a thing or two about glass, including the ones who put the information on the Corning Museum of Glass website (cmog.org if you’re interested), glass is neither liquid nor solid. Its form, or condition, is known as “liquid rigid.” It’s also described as an amorphous solid, meaning its atoms don’t have long-range order, and really not much short-range order, either. I can relate. Glass is created when molten material cools rapidly. In fact, it cools so rapidly that there is not time for a crystalline structure to form. The various atoms are just kind of floating around with one another, so the formation of a grain is not going to happen. For a fun experiment that helps visualize this concept, check out mrsec.psu.edu/content/amorphous-solids.
In nature, glass forms as the byproduct of volcanic activity, or strikes from lightning or meteors. It happens when sand and/or rocks, often high in silica, are quickly heated and then cooled. There are even marine creatures whose silica skeletons are considered a form of natural glass.
People started making glass as early as 3000 B.C. I’m not sure how those first glassmakers figured things out. Where’s Drunk History when you need it? Mother Nature does not provide us with a ready-made pane of window glass or a usable goblet, but she’s right there with the basics, so maybe somebody picked up a chunk of shiny stuff from a newish lava flow, or from a sandy spot that was the scene of a recent lightning strike, and made the connection.
But, back to windshields and windshield glass. The first cars did not have windshields—thus the need for drivers to wear those interesting goggles. It was 1904 before someone thought to include a windshield with the car; those early windshields were basically window glass, however, and had the same properties, one of which was shattering on impact. When there was a crash, drivers and passengers were often injured or killed by glass shards. But, there wasn’t much in the way of consumer protection in those days, nor was there much impetus on the part of car manufacturers to incur more production costs, as they were trying to make more cars as cheaply as possible in order to sell them to as many people as possible.
The year before, a French chemist and artist named Éduoard Bénédictus had made a serendipitous discovery when he knocked over a glass beaker. The beaker broke, but for some reason held its shape. Hmmm. Turns out it had a coating of plastic cellulose nitrate, left over from another experiment. Like those glass makers from 3000 B.C., M. Bénédictus made the connection. In 1909 he filed patent for what was then known as safety glass or laminated glass—it had the product name of Triplex. Car makers were still not on board, and it took a world war for the world to start paying attention to the benefits of glass that didn’t shatter—it was used successfully in gas mask eyepieces. Other enterprising, entrepreneur types, in the interim, were coming up with their own versions of and uses for safety/laminate glass.
Car makers were still dragging their heels, or maybe it was their hand brakes. According to futuretravel.today/through-the-windshield-together-efac522fbe1c (another fun read), the early car manufacturers thought their job, in terms of safety, was to help drivers avoid accidents via things like better brakes or improved handling. If a mishap should occur, the safety of the driver and passengers was not the responsibility of the manufacturers.
Not until people started suing did anything change. One of the most famous, and most aptly named, suits was Pane vs. Ford in 1917. Mr. Pane (no kidding, but I couldn’t find his first name) was involved in an accident while driving his Ford, and attempted to blame the company and the glass in the car for his subsequent injuries. The court ultimately determined it was Mr. Pane’s reckless driving that was the cause, but public sentiment was changing—perhaps because so many people were continuing to be injured from broken glass in car crashes. In 1919, Henry Ford started putting safety glass in all of his cars.
These days, windshield glass is silica sand, soda ash, dolomite, limestone, cullet (broken waste glass), and various oxides like aluminum oxide or potassium oxide. It’s all mixed and heated, terms like float chamber, anneal, autoclave, and lehr are added, a layer of polyvinyl butyral, or PVB, is sandwiched between two layers of glass, and, voila, a windshield!
So should I get mine replaced? Of course, but the crack is not in my line of sight, so, for inspection purposes, it’s not required. Maybe leave it as a science project?