It may be odd to think that metals are made of crystals, because our typical image of a crystal is of a transparent and highly faceted gemstone such as a diamond or emerald. The crystalline nature of metals is hidden from us because metal crystals are opaque, and in most cases microscopically small. Viewed through an electron microscope, the crystals in a piece of metal look like crazy paving, and inside those crystals are squiggly lines—these are dislocations. They are defects in the metal crystals, and represent deviations in the otherwise perfect crystalline arrangement of the atoms—they are atomic disruptions that shouldn’t be there. They sound bad, but they turn out to be very useful. Dislocations are what make metals so special as materials for tools, cutting edges, and ultimately the razor blade, because they allow the metal crystals to change shape.
The melting point of a metal is an indicator of how tightly the metal atoms are stuck together and so also affects how easily the dislocations move. Lead has a low melting point and so dislocations move with consummate ease, making it a very soft metal. Copper has a higher melting point and is stronger. Heating metals allows dislocations to move about and reorganize themselves, with one of the outcomes being that it makes metals softer.
They discovered that a certain greenish rock, when put into a very hot fire and surrounded by red-hot embers, turns into a shiny piece of metal. This greenish rock was malachite, and the metal was, of course, copper. It must have been the most dazzling revelation.
The pyramids of Egypt are an example of what became possible once there were plentiful copper tools. Each block of stone in each pyramid was extracted from a mine and individually hand-carved using copper chisels. It is estimated that ten thousand tons of copper ore were mined throughout ancient Egypt to create the three hundred thousand chisels needed.
Alloys tend to be stronger than pure metals for one very simple reason: the alloy atoms have a different size and chemistry from the host metal’s atoms, so when they sit inside the host crystal they cause all sorts of mechanical and electrical disturbances that add up to one crucial thing: they make it more difficult for dislocations to move. And if dislocations find it difficult to move, then the metal is stronger, since it’s harder for the metal crystals to change shape. Alloy design is thus the art of preventing the movement of dislocations.
Our ancestors didn’t realize that steel was an alloy—that carbon, in the form of charcoal, was not just a fuel to be used for heating and reshaping iron but could also get inside the iron crystals in the process. Carbon doesn’t do this to copper during smelting, nor to tin or bronze, but it does to iron. It must have been incredibly mysterious—and only now with a knowledge of quantum mechanics can we truly explain why it happens (the carbon in steel doesn’t take the place of an iron atom in the crystal, but is able to squeeze in between the iron atoms, creating a stretched crystal).
Like some hugely polite guest, it reacts with the oxygen before the host iron atoms can do so, creating chromium oxide. Chromium oxide is a transparent, hard mineral that sticks extremely well to steel. In other words, it doesn’t flake off and you don’t know it is there. Instead it creates an invisible, chemically protective layer over the whole surface of the steel. What’s more, we now know that the protective layer is self-healing; when you scratch stainless steel, even though you break the protective barrier, it re-forms.
Stainless steel sinks are indomitable and gleaming and seem able to take anything that is thrown at them. In a world where we are keen to dispose of waste instantly and conveniently—from fat, to bleach, to acid—this material has really come through for us. It has ousted ceramic sinks from the kitchen, and would oust the ceramic bowl from the bathroom if we would let it, but we do not yet trust this new metal quite enough for that most intimate of waste disposal jobs.
For, in the end, Brearley did manage to create cutlery from stainless steel, and it’s the transparent protective layer of chromium oxide that makes the spoon tasteless, since your tongue never actually touches the metal and your saliva cannot react with it; it has meant that we are one of the first generations who have not had to taste our cutlery.
Paper yellows with age for two reasons. If it is made from cheap, low-grade mechanical pulp, it will still contain some lignin. Lignin reacts with oxygen in the presence of light to create chromophores (meaning, literally, “color-carriers”), which turn the paper yellow as they increase in concentration. This type of paper is used for cheap and disposable paper products, and is why newspapers yellow quickly in light.
The black-and-white photo of my dad started out as a white piece of paper coated in a fine gel containing silver bromide and silver chloride molecules. In 1939, when the light bouncing off my dad entered the camera lens and fell onto the photographic paper, it transformed the silver bromide and chloride molecules into little crystals of silver metal, which appear as specks of gray on the paper. If the paper had been removed from the camera at this point, the image of my dad would have been lost. This is because all the white areas where there was no image would be flooded with light, causing them instantly to react as well and creating a completely black photo. To prevent this, the photo was “fixed” in a darkroom with a chemical that washed away the unreacted silver halides from the paper. This left only the silver crystals embedded in the layer of gel on the surface of the paper. Once dried and processed it was the image of my dad that enabled him, rather than some other boy, to escape the concentration camps.
Sadly the receipt will not survive long enough for Lazlo to read it. It is already fading, as the thermal paper on which it is printed degrades over time. The reason for this is that printing on thermal paper does not mean adding ink to it. Rather, the ink is already encapsulated within the paper, in the form of a so-called leuco dye and an acid. The act of printing requires only a spark to heat up the paper so that the acid and dye react with each other, converting the dye from a transparent state into a dark pigment. It is this cunning paper technology that ensures that cash registers never run out of ink. But over time the pigment reverts to its transparent state and so the ink fades,
The physicist Enrico Fermi is famous not only for solving fundamental questions of science in the restricted space on the back of an envelope but for formalizing that process. This new form of calculation—the scientific equivalent of a haiku—is called an order of magnitude calculation. This way of looking at the world prizes above all not exact answers but answers that are easily understandable and say something fundamental about the world using only the information available on a bus. They must be accurate by “an order of magnitude,” which is to say that they should be correct within a factor of two or three (i.e., the true value could be as little as a third or as much as three times the result, but no more or less). Such calculations are pretty approximate but they were used by Fermi and others to demonstrate a paradox: the vast number of stars and planets in the universe should provide abundant opportunities for other intelligent life to form and therefore a great likelihood of our having encountered it, and yet, given that we have not encountered it, that same vast number is precisely what shows how rare intelligent life is.
The shininess, smoothness, and weight of the paper have all been shown to be crucial to the success of certain magazines, but less appreciated is the importance of stiffness—or rather, the ease with which the paper will bend: too bendy and the paper gives an impression of cheapness; too stiff and it seems self-important. This stiffness is controlled by the addition of “sizings,”—fine powder additives, such as kaolin and calcium carbonate, that among other things reduce the paper’s ability to absorb moisture, causing inks to dry on its surface rather than infuse its fibers, while also allowing the whiteness of the paper to be controlled. These powders, and the binders that bond them to the cellulose fibers of the paper, create what’s known as a “composite matrix.” (A familiar example of a composite material is concrete, which is similarly composed of two distinct materials: cement, which is the matrix or “binder,” and aggregate, which is known as a “reinforcement.”) Control of this matrix determines the weight, strength, and stiffness of the paper.
The technology relies on the ink being made into a form of the so-called Janus particle. Each particle of ink is dyed so that it is dark on one side and white on the other. The two sides are given opposite electric charges, and so each pixel on the electronic paper can be made dark or white by applying the appropriate electric charge. They are named Janus particles after the Roman god of transitions, who is depicted as having two faces and is often associated with doors and gates. Because the Janus particles are physical ink and need to physically rotate when the text is changed, they cannot be switched as rapidly as the liquid crystal display of an iPad or smartphone,
the case of concrete, if you add too much water there won’t be enough calcium silicate from the cement powder to react with, and so water will be left over within the structure, which makes it weak. Similarly, if you add too little water there will be unreacted cement left over, which again weakens the structure. It is usually human error of this sort that proves the undoing of concrete. Such poor concrete can go undiscovered but then lead to catastrophe many years after the builders have departed. The
with any chemical reaction, if you get the ratio of the ingredients wrong, then you get a mess. In the case of concrete, if you add too much water there won’t be enough calcium silicate from the cement powder to react with, and so water will be left over within the structure, which makes it weak. Similarly, if you add too little water there will be unreacted cement left over, which again weakens the structure. It is usually human error of this sort that proves the undoing of concrete. Such poor concrete can go undiscovered but then lead to catastrophe many years after the builders have departed. The
As with any chemical reaction, if you get the ratio of the ingredients wrong, then you get a mess. In the case of concrete, if you add too much water there won’t be enough calcium silicate from the cement powder to react with, and so water will be left over within the structure, which makes it weak. Similarly, if you add too little water there will be unreacted cement left over, which again weakens the structure. It is usually human error of this sort that proves the undoing of concrete. Such poor concrete can go undiscovered but then lead to catastrophe many years after the builders have departed. The
Concrete is essentially a simulacrum of stone: it is derived from it and is similar in appearance, composition, and properties. Concrete reinforced with steel is fundamentally different: there is no naturally occurring material like it. When concrete reinforced with steel comes under bending stresses, the inner skeleton of steel soaks up the stress and protects it from the formation of large cracks. It is two materials in one, and it transforms concrete from a specialist material to the most multipurpose building material of all time.
Our buildings, roads, and bridges expand and contract like this, observing day and night temperature cycles, as if they are breathing. It is this expansion and contraction that causes a lot of the cracks in roads and buildings, and if it is not taken into account in their design, then the stresses that build up can destroy the structure. Any engineer guessing the outcome of Joseph’s experiments might have assumed that concrete and steel, being so different, would expand and contract at such different rates that they would tear each other apart; that in the heat of the summer or in the depths of winter in Joseph’s garden, the steel would break out of the concrete, causing the pots to rupture. Perhaps this is why it took a gardener to try the experiment at all—it just seems so obvious that it would not work. But, as luck would have it, steel and concrete have almost identical coefficients of expansion. In other words, they expand and contract at almost the same rate. This is a minor miracle, and Joseph was not the only one to notice it. An Englishman, William Wilkinson, had also happened upon this magic combination of materials. Reinforced concrete’s time had come.
Self-healing concrete has these bacteria embedded inside it along with a form of starch, which acts as food for the bacteria. Under normal circumstances these bacteria remain dormant, encased by the calcium silicate hydrate fibrils. But if a crack forms, the bacteria are released from their bonds, and in the presence of water they wake up and start to look around for food. They find the starch that has been added to the concrete, and this allows them to grow and replicate. In the process they excrete calcite, a form of calcium carbonate. This calcite bonds to the concrete and starts to build up a mineral structure that spans the crack, stopping further growth of the crack and sealing it up.
And there is also now a textile version of concrete called concrete cloth. This material comes in a roll and needs only water to be added for it to harden into any shape you like. Although this material has great sculptural potential, perhaps its biggest application may be in disaster zones, where tents made in situ from rolls of concrete dropped from the air can create a temporary city in a matter of days, one that will keep out the rain, wind, and sun for years while rebuilding efforts continue.
But the truth is that cheap design is cheap design whatever the material. Steel can be used in good or bad design, as can wood or bricks, but it is only with concrete that the epithet of “ugly” has stuck. There is nothing intrinsically poor about the aesthetics of concrete. You only have to look at the Sydney Opera House, whose iconic shell enclosures are made of concrete, or the interiors of London’s Barbican Centre to realize that the material is capable of—and in fact makes possible—the greatest and most extraordinary architecture. This has not changed since the 1960s. It is the look of concrete that is now felt to be unacceptable, which means that concrete is now routinely hidden away from sight, providing the core and foundations but not allowed to be visible.
Type V is an extremely dense fat crystal. It gives the chocolate a hard, glossy surface with an almost mirror-like finish, and a pleasing “snap” when broken. It has a higher melting point than the other crystal types, melting at 34°C, and so only melts in your mouth. Because of these attributes, the aim of most chocolatiers is to make Type V cocoa butter crystals. This is easier said than done. They have to be created through a process called tempering, in which preformed “seed” Type V crystals are added during the final process of solidification. These give the slower-growing Type V crystals a head start over the faster-growing Type III and IV crystals, allowing the whole liquid mass to solidify into the denser form of crystal structure before the Type III and IV crystals have a chance to get going.
What happens next is that the ingredients of the chocolate, once bound together by the rigid cocoa butter matrix, are now free to flow to your taste buds. The grains of the cocoa nut, which were once encapsulated in the solid cocoa butter, are now released. Dark chocolate usually contains 50 percent cocoa fat and 20 percent cocoa nut powder (referred to as “70 percent cocoa solids” on the packaging). Almost all the rest is sugar. Thirty percent sugar is a lot. It’s the equivalent of putting a spoonful of sugar in your mouth. Nevertheless dark chocolate isn’t overly sweet; sometimes it’s not sweet at all. This is because at the same time that the sugars are released by the melting cocoa butter, so are chemicals known as alkaloids and phenolics from the cocoa powder. These are molecules such as caffeine and theobromine, which are extremely bitter and astringent. They activate the bitter and sour taste receptors and complement the sweetness of the sugar. Balancing these basic tastes to give the chocolate a rounded flavor is the first task of the chocolatier. The addition of salt as a flavor enhancer, as well as adding another dimension to modern chocolates, has in turn led to chocolate being used as an ingredient in savory dishes: it is the basis of the Mexican dish pollo con mole, which is chicken cooked in dark chocolate.
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