23 JUNE, 2014
By: Maria Popova
“The material world is not just a display of our technology and culture, it is part of us. We invented it, we made it, and in turn it makes us who we are.”
By 1950, Picasso was already an artist world-renowned for his creative products — paintings, sculptures, bronze casts — but only those in his inner circle had a true appreciation of the magic in his process. It wasn’t until a documentary captured him painting on glass, with the camera rolling on the other side of his transparent canvas — a radical proposition at the time — that the world gasped at his breathtaking process. Such was the power of glass.
In Stuff Matters: Exploring the Marvelous Materials that Shape Our Man-Made World (public library), British materials scientist, engineer and educator Mark Miodownik sets out to “decipher the material world we have constructed and find out where these materials came from, how they work, and what they say about us,” stripping them down to the elemental human desire that brought each of them into being and exploring how the material science that produced them affects the broader context of our lives. Miodownik paints the backdrop:
This stuff is important. Take away the concrete, the glass, the textiles, the metal, and the other materials from the scene, and I am left naked, shivering in midair. We may like to think of ourselves as civilized, but that civilization is in large part bestowed by material wealth… The material world is not just a display of our technology and culture, it is part of us. We invented it, we made it, and in turn it makes us who we are.
Picasso paints on glass, 1950. Click image for more.
One of the most interesting, and unexpectedly so, materials he examines is glass — a substance so ubiquitous in modern life and yet, at its best, so invisible. Duality and paradox, in fact, seem to be baked into the very nature of glass — quite literally. Before he plunges into the meaty interestingness of this singular material and its cultural history, Miodownik explains the no less interesting basic science of how sand becomes glass — one of the most remarkable transmutations in the observable physical universe:
Sand is a mixture of tiny bits of stone that have fallen off larger bits of rock as a result of the wind and the waves and other wear and tear that stones have to put up with. If you take a close look at a handful of sand you will find that a lot of these bits of stone are made of quartz, a crystal form of silicon dioxide. There is a lot of quartz in the world because the two most abundant chemical elements in the Earth’s crust are oxygen and silicon, which react together to form silicon dioxide molecules (SiO2). A quartz crystal is just a regular arrangement of these SiO2 molecules, in the same way that an ice crystal is a regular arrangement of H2O molecules or iron is a regular arrangement of iron atoms. Heating up quartz gives the SiO2 molecules energy and they vibrate, but until they reach a certain temperature they won’t have enough energy to break the bonds that hold them to their neighbors. This is the essence of being a solid. If you keep heating them, though, their vibrations will eventually reach a critical value — their melting point — at which they have enough energy to break those bonds and jump around quite chaotically, becoming liquid SiO2. H2O molecules do the same thing when ice crystals are melted, becoming liquid water.
But here’s the rub — when you put that liquid water into the freezer, it has no trouble refreezing into ice crystals. And you can do it again and again, melting and freezing into oblivion. Unlike water, however, SiO2 has a hard time forming a crystal once cooled down — it’s almost as if the molecules forget how to assemble into that formation. (There is a fascinating Radiolab episode about this notion.) What’s more, to stay with the anthropomorphism, the molecules grow lethargic — as they lose energy during the cooling, they have an even harder time getting into the appropriate position. Out of this forgetful laziness comes the miracle of glass — “a solid material that has the molecular structure of a chaotic liquid.”
This is where one of glass’s inherent paradoxes arises: If SiO2‘s inability to form a quartz crystal is all it takes to produce glass, one would imagine making it is a piece of cake. Just set a bunch of sand ablaze and watch it glassify. Alas, it’s not nearly as easy — or else Earth’s deserts would have easily turned to glass eons ago. The reason this hasn’t happened is twofold. Miodownik explains:
The first [problem] is that most sand doesn’t contain the right combination of minerals to make good glass: the brown color is a dreaded sign in chemistry, a clue that you have a mixture of impurities. It is the same with paints: random combinations of colors don’t yield pure results; instead you get brownish-gray hues. While some additives, so-called fluxes, such as sodium carbonate, will encourage the formation of glass, most will not. Unfortunately, despite being mainly quartz, sand is also made up of whatever the wind blows in its direction. The second problem is that even if the sand has the right chemical composition, the temperatures needed to melt it are around 1200 ° C, much hotter than any normal fire, which tends to be in the region of 700–800°C.
One of Antoine de Saint-Exupéry's original watercolors for 'The Little Prince,' 1943. Click image for more.
What does the trick, however, is a lightning bolt, which can heat the desert to more than 10,000°C — a temperature well capable of melting the sand. When that happens, shafts of glass called fulgurites form — named after fulgur, the Latin for “thunderbolt.” Because the sand is impure, the fulgurites are murky and nearly opaque. Except in certain curious circumstances:
A lightning bolt will do the job, though. When one of these strikes the desert it creates temperatures in excess of 10,000°C which are easily high enough to melt the sand, creating In one part of the Libyan Desert, there is an area of exceptionally pure white sand, comprised almost entirely of quartz. Search this part of the desert and you may find a rare form of glass that looks nothing like a scruffy fulgurite but which has instead the jewel-like clarity of modern glass. A piece of this desert glass forms the centerpiece of a decorative scarab found on the mummified body of Tutankhamun. We know that this desert glass was not made by the ancient Egyptians because it has recently been established that it is twenty-six million years old. The only glass we know like it is Trinitite glass, the glass formed at the site of the Trinity nuclear bomb test in 1945 at White Sands, Nevada. Given that there was no nuclear bomb in the Libyan Desert twenty-six million years ago, the current theory is that the extremely high temperatures that would have been needed to create such optically pure glass must have been produced by the high-energy impact of a meteor.
But rather than a mere curious oddity, fulgurites embody the hidden potentialities in glass not only as a participant in the cultural and natural history of Earth but also as a teller of that story — because ancient fulgurites trap air bubbles as they form, they offer climate scientists an invaluable record of the past.
In fact, Miodownik’s most interesting point about the cultural role of glass has to do with science — but not in the expected direction of the relationship. As is the case with most world-changing innovations, the inventor and the popularizer who ultimately leads to mass adoption of the invention are different individuals, often years apart. The Greeks and the Egyptians had pioneered glass-making, but the Romans were the ones who introduced it into daily life. After discovering the mineral natron — a naturally occurring form of baking soda — they were able to make relatively clear glass at much lower temperatures than what would be needed to melt pure quartz. They built special furnaces for manufacturing glass in bulk, which they then distributed across the Roman Empire — so the glass revolution wasn’t merely one of technology, but also of infrastructure and marketing. Suddenly, glass was a material available to and affordable for the average citizen — an achievement based not on harnessing a novel technology but, essentially, on setting Moore’s Law into motion.
The crowning achievement of the Roman glass age was the invention of the window — Latin for “wind eye” — that filled the gaping, wind-weary openings on building walls. It was, as Miodownik notes, the birth of our modern obsession with architectural glass. The Romans also invented the modern mirror, which prior to the glass revolution consisted of a highly polished metal surface that rendered a much duller and fuzzier image. The glass-covered mirror not only gave a crisper image, but was also far cheaper and easier to produce.
But the most interesting part of the glass story has to do with the Scientific Revolution itself. Fast-forward to a millennium after the collapse of the Roman Empire, and China has cultivated the world’s greatest mastery of materials through extraordinary craftsmanship of wood, paper, ceramics, and metals.
And yet, they largely ignored glass.
Meanwhile in Europe, scientists and inventors were hard at work building the telescope and the microscope — the powerhouse duo of the Scientific Revolution. In what’s perhaps his most intriguing point, Miodownik argues this may have planted the seed for the growing rift in technological advances and corresponding material wealth between the East and the West over the centuries that followed. Miodownik writes:
The disdain for glass in the East lasted all the way up until the nineteenth century. Before then, the Japanese and Chinese relied on paper for the windows of their buildings, a material that worked perfectly well but resulted in a different kind of architecture. The lack of glass technology in the East meant that, despite their technical sophistication, they never invented the telescope nor the microscope, and had access to neither until Western missionaries introduced them. Whether it was the lack of these two crucial optical instruments that prevented the Chinese from capitalizing on their technological superiority and instigating a scientific revolution, as happened in the West in the seventeenth century, is impossible to say. What is certain, though, is that without a telescope you can’t see that Jupiter has moons, or that Pluto exists, or make the astronomical measurements that underpin our modern understanding of the universe. Similarly, without the microscope, it is impossible to see cells such as bacteria and to study systematically the microscopic world, which was essential to the development of medicine and engineering.
Whether the relationship between glass technology and the seventeenth-century scientific revolution really is a simple case of cause and effect is an open question. It seems more likely that glass was a necessary condition rather than the reason for it. However, there is no doubt that glass was largely ignored in the East for a thousand years.
Backtracking from these complex potential sociopolitical effects, the most remarkable property of glass remains its most elemental — its crystalline clarity and tantalizing transparency, the mysterious quality that lets light pass through it and thus sets it apart from other solids. Miodownik digs deeper to extract the real — and appropriately counterintuitive — mystery:
After all, glass contains all of the same atoms that make up a handful of sand. Why in the form of sand should they be opaque and in the form of glass transparent and able to bend light? Glass is made of silicon and oxygen atoms, as well as a few other sorts. Within every atom there is a central nucleus, which contains protons and neutrons, surrounded by varying numbers of electrons. The size of the nucleus and the individual electrons is tiny compared to the overall size of the atom. If an atom were the size of an athletics stadium, the nucleus would be the size of a pea at its center, and the electrons would be the size of grains of sand in the surrounding stands. So within all atoms — and indeed all matter — there is a majority of empty space. This suggests that there should be plenty of room for light to travel through an atom without bumping into either an electron or the nucleus. Which indeed there is. So the real question is not “Why is glass transparent?,” but “Why aren’t all materials transparent?”
Illustration from Disney's 'Our Friend the Atom,' 1956. Click image for more.
Miodownik extends the metaphor to offer an elegant explanation:
Inside an atomic stadium … the electrons are only allowed to inhabit certain parts of the stands. It is as if most of the seats have been removed and there are only certain rows of seats left, with each electron restricted to its allotted row. If an electron wants to upgrade to a better row, it has to pay more—the currency being energy. When light passes through an atom it provides a burst of energy, and if the amount of energy provided is enough, an electron will use that energy to move into a better seat. In doing so, it absorbs the light, preventing it from passing through the material.
But there is a catch. The energy of the light has to match exactly that required for the electron to move from its seat to a seat in the available row. If it’s too small, or to put it another way, if there are no seats available in the row above (i.e., the energy required to get to them is too large), then the electron cannot upgrade and the light will not be absorbed. This idea of electrons not being able to move between rows (or energy states, as they are called) unless the energy exactly matches is the theory that governs the atomic world, called quantum mechanics. The gaps between rows correspond to specific quantities of energy, or quanta. The way these quanta are arranged in glass is such that moving to a free row requires much more energy than is available in visible light. Consequently, visible light does not have enough energy to allow the electrons to upgrade their seats and has no choice but to pass straight through the atoms. This is why glass is transparent. Higher-energy light, on the other hand, such as UV light, can upgrade the electrons in glass to the better seats, and so glass is opaque to UV light. This is why you can’t get a suntan through glass, since the UV light never reaches you. Opaque materials like wood and stone effectively have lots of cheap seats available and so visible light and UV are easily absorbed by them.
This makes one wonder about popular brands of eyewear advertising a “UV filter” — but then again, saying that all glasses filter UV light by definition is a decidedly less marketable message.
The interaction between light and glass brings us full-circle to the heart of the scientific revolution and Sir Isaac Newton, whose genius — at least when it came to glass — was one of reverse-engineering. Miodownik highlights his landmark contribution:
It wasn’t until 1666 that Isaac Newton realized that what was blindingly obvious was blindingly wrong and came up with the real explanation. Newton’s moment of genius was to notice that a glass prism not only turned “white” light into a mixture of colors, but could also reverse the process. From this, he deduced that all of the colors created by a piece of glass were already in the light in the first place. They had traveled all the way from the sun as a ray of mixed light, only to be split up into their constituent colors when they hit the glass. The same thing would happen if they hit a drop of water, too, since this was also transparent. At a stroke, Newton had for the first time in history managed to explain the main features of the rainbow.
Considering these and many other cultural contributions we owe to glass — it gave chemists clear beakers and let them actually observe the reactions taking place; it radically changed how beer is drunk by transforming it from a once-murky brew to be experienced only in the mouth to a golden gift to be beheld with the eyes — Miodownik contemplates rather beautifully what’s perhaps the greatest cultural paradox of glass:
We have no great love for the material that has made this possible. People do not tend to wax lyrical about glass in the way that they do about, say, a wooden floor or a cast-iron railway station. We do not run our hands down the latest double-glazed panel and admire the sensuality of this material. Maybe this is because in its purest form it is a featureless material: smooth, transparent, and cold. These are not human qualities. People tend to relate more to colored, intricate, delicate, or simply misshapen glass, but this is rarely functional. The most effective glass, the stuff we build our modern cities from, is flat, thick, and perfectly transparent, but it is the least likable, the least knowable: the most invisible…
For all its considerable importance in our history and our lives, glass has somehow failed to win our affections [and] has not become part of the treasured fabric of our lives. The very thing that we value it for has also disqualified it from our affections: it is inert and invisible, not just optically, but culturally.
Stuff Matters is an illuminating and addictively absorbing read in its entirety. Complement with Richard Feynman’s spectacular metaphor for the universe, which wouldn’t be possible without glass.
Donating = Loving
Bringing you (ad-free) Brain Pickings takes hundreds of hours each month. If you find any joy and stimulation here, please consider becoming a Supporting Member with a recurring monthly donation of your choosing, between a cup of tea and a good dinner.
You can also become a one-time patron with a single donation in any amount.