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The Science of Middle-earth -- Making Mithril
-- Olog-hai

The fabric of Middle Earth is almost the same as that of the real world of today. There are rocks and water, wood and stone, silver and gold. Almost, but not quite, because there is also mithril. A metal harder than steel, yet as lustrous and as ductile as silver. Although found in small quantities in the Blue Mountains, the discovery of mithril beneath Caradhras in the Misty Mountains led to the spectacular rise and fall of Moria. But what is it?

On the level of the story, mithril is as much a fantasy creation of The Lord of the Rings as elves and hobbits, and as such does not require a prosaic identification with anything in the modern world. In any case, it is a tacit assumption that the last accessible veins were exhausted by the end of the Third Age, so if it were once a real substance, there isn't any more of it: or if there is, it would be too difficult to find. The attraction of mithril lies in its inaccessibility. In what follows, therefore, I am not going to say that mithril 'really was' this substance or that. To do that would destroy the magic -- and, in any case, I do not believe that Tolkien ever left any specific notes about its identity. However, that should not prevent us from looking for materials in the modern world that might have the properties of mithril that Tolkien did describe, if only in the spirit of a crossword puzzle, or a riddle game.

So, let's start with what Tolkien told us about marvellous mithril -- a shiny metal, easy to extract, stronger and harder than steel, and yet very ductile, which means that it is easily worked by a smith or jeweller at room temperature, or at worst with the help of the kind of forge available to any blacksmith. Finding a single material that is both strong and ductile at relatively low temperatures is a tall order, because these properties seem to be contradictory. Strong metals have a microscopic crystalline structure that resists deformation until a critical point is reached, when they start to crack. This means that strength often goes with brittleness, which is precisely the wrong property of a metal that is easily workable. Can you have a metal that is strong and ductile at the same time, or will mithril forever remain in the realm of fantasy?

Let's break down the problem and see what kinds of materials might suit. Mithril is obviously a metal, and metals come in three varieties: if they are not chemical elements, they are alloys in which various elements are mixed together to suit the purposes of the engineer; or they are chemical compounds -- substances in which the constituent chemical elements are combined in fixed ratios. Water, for example, is a compound in which there are always two atoms of the element hydrogen to every one of oxygen -- H2O.

Most of the metals we're familiar with are chemical elements. This means that they are pure substances that can't be broken down into anything simpler. None, however, manage to be both strong and ductile at the same time. If an elemental metal is ductile, it is also rather weak. This tends to apply to those metals that are most easily extracted from their parent rocks, and therefore known to metallurgists since antiquity: elements such as gold, silver, copper, mercury, tin and lead. If an elemental metal is strong, such as iron, it is likely to be heavy, brittle, or both. Lightweight, lustrous metals that might fit the bill -- such as the magnesium, aluminium or titanium of today's high-tech applications -- must first be extracted from their ores using prodigious amounts of energy and the kind of heavy industrial-scale equipment unlikely to have been used by the dwarves or even the Noldor at the height of their power, with the possible exception of Fëanor. However, we know that mithril was easy to extract, and occurred in identifiable veins, so it couldn't have been one of these metals anyway. Mithril as a chemical element seems to be out. 'True silver' remains plain old silver, nothing more.

Alloys might offer an easy alternative. Elemental iron on its own is hard, but it rusts. Add a little vanadium, chromium and carbon, though, and it becomes an alloy called stainless steel -- rustproof and very much harder than pure iron. Brass is a mixture of copper and zinc, and bronze is a mixture of copper and tin. There is even an alloy called electrum, a combination of silver and gold in various proportions used in ancient times for coinage.

Although alloys are invariably man-made, one could imagine mithril as a natural alloy of, say, iron, silver and a little carbon, but that seems unsatisfactory. Tolkien's mithril is nothing so prosaic as an alloy: it always seems to have a distinct identity, and properties recognizable as such down the ages -- this would not be true of an alloy, whose properties can change according to the recipe used by the metallurgist.

If mithril is neither a chemical element nor an alloy, the only choice left is that it is a chemical compound -- a substance made of fixed, unvarying ratios of chemical elements, chemically bound together rather than simply mixed. It so happens that there is a class of chemical compounds called 'intermetallics'. Like alloys, intermetallics consist of two or more metals combined. Unlike alloys -- and this is crucial -- the metals are always fixed ratios, because intermetallics are true compounds, as opposed to mixtures. The intermetallic compound Ni3Al, for example, is not an arbitrary mixture of nickel and aluminium, but a compound with a definite crystal structure in which there are always three nickel atoms for every one of aluminium. Intermetallics, like alloys, are products of technology rather than nature, but is it possible to think of mithril as a kind of naturally occurring intermetallic?

Well, nearly. Intermetallics seem to have many of the properties of mithril. They are light, durable, strong and shiny, and they have all kinds of interesting magnetic and electrical properties that might be useful should you wish to design, say, a kind of ink that is only visible in starlight and moonlight. But there is a huge downside -- intermetallics are very brittle. This deficiency of chemical character has prevented the widespread use of intermetallics in technology and industry: and would be no good for mithril, either.

So we seem to be stuck. Or we would be, were it not for the extremely recent discovery of a family of simple intermetallics that are shiny, strong, light -- and ductile. They all consist of a regular metal, such as copper or silver, allied with one of a member of the intriguing and exotic 'rare earth' metals, hardly known to the general public outside Tom Lehrer's song The Elements. The researchers' favourite is yttrium silver, an intermetallic in which atoms of silver and atoms of the rare-earth element yttrium occur in precisely equal amounts. Yttrium silver is so ductile that a wire can be stretched to a fifth again its length before it snaps. There is something about its crystal structure, not yet fully understood, that allows it a degree of plastic flow without its breaking into ragged fragments.

I conclude that yttrium silver would make a good real-world candidate for mithril (and as Quickbeam pointed out to me the other day, even the name 'yttrium silver' has an allure all its own.) Yttrium silver is, however, totally synthetic: as far as we know, no seam of the stuff waits to be mined out of some unexplored cavern. On the other hand, exotic minerals exist that are known only from one or two localities on Earth, formed by circumstances of temperature and pressure unique to that place only. Who is to say that the silver in the Silverlode did not contain a little yttrium?

One property of mithril I have not discussed is its 'hardness'. In the film of Fellowship, Bilbo describes mithril as being as 'hard as dragon scales'. Allowing that Bilbo was being poetic or figurative rather than scientifically accurate, it is a safe bet that dragon scales -- when not additionally encrusted with gems -- are coated with enamel, the hardest substance produced by living creatures, and the same substance that coats your teeth. So how hard is that?

When seeking to identify a gem, jewellers assess hardness by the ability of one substance to scratch another. This concept was formalized in 1822 by the German mineralogist Friedrich Moh, and the Moh scale of hardness is still used today. In the Moh scale, diamond has a hardness of 10. Diamond is still the hardest known naturally occurring substance -- nothing matches it, or scratches it. Corundum (that is, ruby or sapphire) can be scratched by diamond, and has a hardness of 9. Topaz (with a hardness of 8) can be scratched by rubies but itself scratches quartz (hardness of 7), and so on, all the way down to flaky gypsum (2) and powdery talc at the bottom, with a hardness of 1. On this scale, teeth come in at around 5, the hardness of the mineral apatite -- which is not surprising, as this is the same mineral that forms the basis of bones and teeth. One would expect mithril to be at least as hard as that: good-quality steel has a hardness of around 6.5, so Bilbo's equation of mithril with dragon scales is about right.

Mithril is just the right thing to make a tough corselet of mail rings. But any skilled smith might have been able to have enhanced its properties still further, by controlling the crystalline structure of the material -- an important determinant of its hardness. Swordsmiths can control the properties of blades by forging them in just the right way to ensure that the edge is extremely hard and brittle, but the main body of the blade is flexible. A key step in the forging of a samurai sword involves wrapping the sword in clay, with only the edge exposed. The sword is then heated to above what is known as the 'martensitic' transition, when the steel adopts a different kind of crystalline configuration. The hot blade is then thrust very suddenly into a pool of cold, stagnant water (I believe you can see elven swordsmiths doing something similar as they reforged Narsil in the trailer to ROTK.) The rapid cooling of the edge produces a fine-grained microcrystalline structure that is very hard, but very brittle. The bulk of the blade, shielded by the clay, cools more gently, resulting in a structure with much larger crystal grains, fewer defects (which tend to inhabit the areas between grains) and therefore greater resistance to fracture.

Although a mail-shirt of mithril rings isn't quite the same thing as a sword, one might imagine how a smith might put it through a quench-hardening process. This would leave the core of each ring strong but flexible, and the outer surface brittle but very, very hard -- and with a network of microscopically fine cracks that might give the material a sparkly appearance if turned in the light.

Quench hardening does not work with metals that do not undergo the martensitic transition, but the elastic properties of metals more generally can be controlled by varying their microstructure through careful manufacture. There is, however, an intriguing alloy of nickel and titanium that undergoes the martensitic transition -- and which, therefore, could be quench-hardened. The wonderful property of this alloy is that it is a 'memory' metal -- it is light and flexible, but springs back to its original shape once bent. These properties make it ideal for high-tech spectacle frames, even though it was originally developed for use in the light-weight, super-tough protective shells of the warheads of intercontinental ballistic missiles, designed to stop them burning up on atmospheric re-entry. Now, go tell that to the cave trolls.

Next time I shall discuss, among other things, an amazing substance with a hardness that goes all the way up to 11.

I'd like to thank Karl Ziemelis and Edmund Gerstner for their invaluable help in researching and writing this article.

Source: A family of ductile intermetallic compounds by K. Gschneidner, Jr. et al, Nature Materials vol. 2, pp. 587-590 (2003)

-- Olog-hai

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