8 How to Kill a White Walker

The Physics of Dragonglass

When he opened his eyes the Other’s armor was running down its legs in rivulets as pale blue blood hissed and steamed around the black dragonglass dagger in its throat. It reached down with two bone-white hands to pull out the knife, but where its fingers touched the obsidian they smoked.

—Samwell Tarly fighting a White Walker, A Storm of Swords

Valyrian steel can make short work of a White Walker, but there aren’t many Valyrian steel blades left in Westeros. This presents a problem for the entirety of Westeros, especially with winter’s approach and the problems from the north. Samwell Tarly was lucky enough to accidentally figure out that dragonglass can also kill White Walkers, too. It seems that the only things that can kill the ice beings is something made by dragons. Considering the book series is titled A Song of Ice and Fire, this isn’t exactly shocking. Luckily, Daenerys believes Jon and lets him mine her glass, so to speak. Physics says steel won’t work to kill a White Walker, as Sam found out. But, dragonglass—or obsidian, as it is known in both our world and Westeros—will do the job well. Why? What makes dragonglass and its real-life counterpart so special?

As GRRM’s name for it would imply, obsidian is a type of glass. In general, glasses are shiny, often transparent, smooth, and tend to feel cold. The most common type of glass—the kind we interact with on a daily basis—is made from silicon dioxide (SiO₂), which has the same chemical formula as sand. Sand isn’t exactly super shiny, and it is definitely not transparent. You might assume that it’s something about the way the atoms are ordered in window glass that gives it its unique properties. If so, can anything be turned into a glass? How does the arrangement of atoms make an object either opaque or transparent? What does the crystal structure of glass look like? What makes some glasses dark and others clear? How is it supposed to help us defeat the army of the dead? So many questions about glass! You’d think asking a scientist would help answer some of them, but seeing as scientists can’t even agree on whether glasses are liquids or solids, that might be tricky. Hopefully, I can at least shed some light on (or through) the science of glass.

So far, I’ve talked about other solids: rock, ice, steel, and Damascus steel, to be exact. All of them have a defined crystal structure; that is, the atoms sit in a particular order throughout the crystal. A solid’s properties are macroscopic representations of what the atoms are doing at the microscopic level. The BCC and FCC lattices and metallic bonds are what gives metals their special properties—ductility, conductivity, and malleability, to name just a few. To understand glass and, more specifically, how it might operate at cold temperatures, it’s important to start by understanding what glass looks like at an atomic level. Glass is what’s called an amorphous solid, which means it doesn’t really have a structure. It’s basically as if the molecules played freeze tag—one moment they are freely running around in a liquid state, and then next thing they know they are all stuck in one place. It’s a solid, but there’s no long-range order. The atoms and molecules have stopped moving, but it happened so suddenly that they haven’t had time to organize themselves. This type of arrangement is very similar to a liquid, which is why sometimes people see glass as a solid and some see it as a highly viscous, slow-moving solid. There’s even a very famous experiment, which I’ll discuss later in the chapter, that shows it can be a liquid. Hopefully by the end of this chapter you will have a greater appreciation for the stuff you’ve probably run into by accident while carrying coffee.

Solid, Liquid, or Both? What Is Glass?

Whether or not it’s a good analogy, I always think of glass as a liquid that’s playing freeze tag. It inevitably makes me think of third-graders at recess. If they are running around outside and are yelled at to stop, they’ll stop exactly where they are in no particular order, just motionless disorder. If they are told it’s time to head inside and sit down, they’ll take time to line up and file into their classroom. Most liquids do the same thing, except instead of being told to stop, they are cooled down. If the cooling is done quickly, they don’t have the chance to slowly form into orderly crystals like they want to. Remember from the chapters about steel that quenching creates a solid structure that is markedly different, and better, than the ones created with slow cooling. A solid is defined as having closely packed molecules arranged in a regular array—a rigid structure that does not deform or flow to fill a container or a specific volume and cannot be compressed easily the way a gas can. The solids I’ve talked about until now are called crystalline solids, meaning they have a crystal structure. An amorphous solid, by contrast, is one with no long-range order. It still has the properties of a solid (for the most part) but no one part has the same order as any other part. The word amorphous comes from a Greek word meaning “without shape.” Although the final glass has a shape on a macroscopic level, microscopically, it does not (figure 8.1). Another way to understand amorphous solids at the microscopic level is this: Imagine you are a tiny observer sitting on a crystal in a crystalline solid. As you look around, you see a regular array of atoms. You say, “OK, there’s sodium to my right, and down there I see chlorine.” This gives you a sense of directionality and orientation within the solid. Now, put yourself inside an amorphous solid. The first thing you notice is that everything looks the same in every direction. There is no structure to orient yourself around, to the extent that if you closed your eyes and took five steps to the left and opened your eyes again, your surroundings would give no indication that your location had changed. This gets at the more mathematical definition of amorphous, meaning that there is no geometrical reference frame for defining motion within the solid.

The study of glass has a long history. Just like steel, it was first made about 5,000 years ago. The first scientific papers on the properties of glasses were published about 200 years ago. Considering writing had barely been invented when glass was first studied, it’s not surprising that it took a while for articles to be published. John Mauro and Edgar Zanotto published a fabulous history of the study of glass over the past 200 years.1 They found that the rate of publication of papers on glass has increased exponentially since 1945. More recently, the number of patents has surpassed the number of papers published. As you will see in chapter 10 when I talk about Greek fire, there’s a difference between science and technology. With more patents being issued, glass has moved from an area of fundamental research to a focus of really impressive technological advances. The glass on your smartphone is just one amazing example. Automotive glass is another precisely engineered technology.

Many different types of materials can be made into glasses and the method is generally the same: heat something until it melts and cool it quickly enough that it doesn’t have time to crystallize. Just as different materials have different melting points, they also have different rates of cooling required to freeze them into a glass. For something like quartz, which is composed of silicon dioxide (also the main ingredient in window glass), once it’s been heated to a certain point, it can be cooled in air and become a glass. It’s almost impossible to turn it back into a crystal. A substance such as steel can be pushed into a glass phase by being cooled at a rate of about 1 million degrees per second. If people really wanted to make a fabulous sword, metallic glass would have been the way to do it. Compare that to the cooling rate of quenching a sword, which is about 1,000 degrees per second, maybe less. This is why steel, even if heated until molten, doesn’t become a glass when quenched. The temperature at which something changes from a molten state to a glass is called, unsurprisingly, the glass transition temperature, or T_g. One question that arises is how to determine when something becomes a glass. T_g is different from the melting point, which is where a material would go from a liquid to a crystalline solid. With a melting point, there is a quick jump from ordered solid to disordered liquid. Because a material sort of slides into glass form, there’s no quick and easy way to determine the point at which it becomes a glass. There is a huge question of exactly when something goes from liquid to glass on a microscopic level. In a crystalline solid, it’s pretty easy to see when the atoms and molecules are all sitting in an ordered way. In a glass, there’s just a point where the molecules stop moving enough to be called a glass. There are different ways to determine when this point is reached. The most common involves measuring how quickly the molecules are moving or how stiff the material is. Once the molecules are moving slowly enough and the material is stiff enough, it’s considered a glass. Glasses are kind of like obscenity—hard to define, but you know it when you see it. It’s worth noting that the only way to produce a glass is to heat it and quench it into place. Nothing has a ground state as a glass. The atoms don’t usually choose to line up in an amorphous disordered state.2

I know I defined glass as an amorphous solid and that I have been using the two terms interchangeably up to this point. Many people do that, but some scientists are picky about it. Not surprisingly, however, they aren’t always picky in the same way. A paper by P. K. Gupta does a great job of summing up the various definitions of glasses versus amorphous solids.3 A glass is defined as something where the order over a very short range is indistinguishable from that of the same material in a liquid state. An amorphous solid is one that doesn’t have long-range order or crystal structure, but it is possible to tell the difference between a liquid and a solid in the short range. This is probably more useful to know for advanced bar trivia than for this discussion, but it’s still interesting.

One of the hallmarks of glass, as anyone who’s managed to drop a glass of wine at a cocktail party knows, is that glass is brittle and shatters easily. Going back to the terminology of chapters 5 and 6, glass is not very tough and not at all ductile. What makes metal so ductile is the crystal structure that allows the atoms to roll over each other when pushed. With too much carbon in the way, this rolling is impeded, and the material becomes brittle and prone to fracture when forged. When it breaks, it does so along dislocation planes, and oftentimes the grain boundaries act like little roadblocks stopping the cracks from progressing. The metal can slip and roll and move without structurally failing. In glasses, however, there’s no order at all. The atoms can’t roll over each other when pushed, and there are no easily defined fracture planes. When pushed, the molecules have nowhere to go and are under a huge amount of stress, so they crack. Because there is no long-range order, there are no roadblocks to stop the crack from continuing. The material simply shatters. And, in contrast to crystalline solids, there typically is not an ordered pattern to the cracking. You’ll notice that when a crystal shatters, the small pieces look similar to the original pieces; after all, little rocks are just tiny versions of big rocks. But when glass shatters, you see a whole variety of shapes and sizes: some tiny, deathly sharp needles; some big chunks that are easy and safe to pick up.

Glass can be strengthened through a process called tempering, which I mentioned when talking about regular steel. Tempered glass is about four times stronger than normal glass and has the added benefit of shattering into small, regular pieces with low stabbing possibility. Tempering glass is very similar to tempering steel. It is heated to just below the melting temperature and then quenched with air. The outside cools much more quickly than the inside. Unlike with steel, where the process results in a different form of steel on the outside from the one on the inside, the whole thing remains glass because glass doesn’t really have any structural or crystal phases. The inside cools much more slowly, however, and as it cools it pulls back on the outside, causing stress. This makes for stronger glass, but when that tension is released after too much pressure is applied, the glass basically explodes. Pyrex is a great example of tempered glass. It’s the tempering process that allows you to bake delicious brownies in a Pyrex dish and stay worry-free if you drop the hot dish on the ground or run cold water on it before it cools.4

One of the most beautiful examples of glass is the stained-glass window. The development of both glass and steel happened around the same time and both followed a similar path. Initially, artisans would use whatever material was available to create glass and, as with steel, it came out however it came out: sometimes it worked, sometimes it didn’t. Glass could be made in a huge array of colors depending on the materials used to make it, and eventually it became clear as to which materials would produce certain colors. The colors come from trace minerals or elements mixed in with the raw materials of the glass. Iron oxide, for example, will tint glass green, whereas cobalt will lend its characteristic blue hue. One of my favorite glass additives is uranium. It’s not the safest, but glass with uranium mixed in glows spectacularly under a black light. (You can get uranium marbles on Amazon and see for yourself.) Many of these colors, however, will fade over time. For a 1,000-year-old church window, this can pose a problem. Ancient glassmakers stumbled on a solution, however: nanoparticles. Turns out artisans were pretty darn good at using them without knowing it. Adding gold and silver to glass created beautiful colors that didn’t fade. One of the classic examples is a cup from Rome dating back to the 13th century AD. The cup appears green at first look but red when light shines through it. Scientists imaged the glass and found that it contained gold and silver nanoparticles. The mechanism by which these particles were created is still unclear, but medieval artisans knew how to use them to their advantage. When light hits the nanoparticles in the cup, it excites the electrons on the surface of each tiny little ball. In a sheet of gold, the light is reflected normally and the sheet looks gold, but with nanoparticles, the electrons are so close together that they have very little room to move. They preferentially reflect red light, making the nanoparticles, and thus the goblet, appear red.5

There are several examples of glasses being created in nature as well as by accident. One type of natural glass is fulgurite. When lightning strikes sand, it is hot enough to melt some of the silicon dioxide, which then solidifies back into a glass. Glass is created along the path the lightning takes through the sand. This creates beautiful pieces of glass that look like glass branches. Humans accidentally on purpose did something similar at the Trinity nuclear test site in New Mexico. During the first nuclear bomb test, sand was drawn up into the fireball and melted. It was so hot that the molten sand rained down, cooling on its way to the ground and creating trinitite. Many scientists from that time still keep pieces of trinitite on their desks or have passed it down to their students. Trinitite is mildly radioactive, but not enough to harm anyone. Still, it is now illegal to remove it from the test site. Trinitite is generally light green in color and has a complex structure due to its unusual creation. Volcanoes can also create glass—obsidian, to be exact—but I’ll save that discussion for later.

The Sad Case of the Pitch of John Mainstone

In 1927, Professor Thomas Parnell of the University of Queensland in Brisbane, Australia, walked into his physics class with pitch, a funnel, and the goal of showing his class that sometimes solids weren’t solid but liquids that moved very, very slowly. He took a block of pitch, heated it, and put it into the funnel. Pitch isn’t technically a glass but is a great example of something appearing to be a solid but acting like a liquid. That, and this is one of my favorite stories in science. Then he waited. And waited. After allowing the pitch to settle for three years, and probably watching some of the students in that original class graduate, he put a beaker under it and cut the tip of the funnel. Then he waited some more. Those original students graduated med school and law school and had babies. During all this time, the pitch was ever so slowly creeping out of the bottom of the funnel and forming a drop. It looked just like a water drop, only it wasn’t moving on any scale we can see. As the drop of pitch got closer and closer to the bottom of the beaker, the experiment was monitored more and more closely. Parnell waited (and waited and waited) to for the moment when the pitch drop fell. As the drop slowly moved down, it eventually hit the bottom of the beaker but was still attached to the mass of pitch. “Falling” was when the drop officially broke that last connection with the pitch in the funnel. Though it took years for the drop to hit the beaker, the actual break would take only a fraction of a second. Eight years after the funnel was first cut, in December of 1938, the drop, which had been sitting on the bottom of the beaker, finally cracked off of the rest of the pitch. After eight years, the actual drop took only a fraction of a second. No one saw it. A second drop fell within Parnell’s lifetime in 1947, and he did not see that one either. The third drop fell in 1954, after Parnell’s death and before anyone else seemed to care much. In 1961, John Mainstone joined the faculty and became the custodian of the experiment (figure 8.2).

By this point, 13 years after Parnell’s death, the experiment was shoved in a cabinet. Mainstone wanted to watch and hauled it out from obscurity. Another drop had fallen sometime in the intervening years, bringing the count to three drops in 31 years. Mainstone was determined to see the drop fall. He didn’t have long to wait. A fourth drop fell in 1962. He missed it. Another in 1970. Though Mainstone watched religiously, he missed it once again. He was so close in 1979—he looked at it on a Friday, came into the office to monitor it that Saturday, and decided that it would hold off on breaking until Monday. It did not, and Mainstone missed it. Again. He was determined not to miss it in 1988. He kept vigil over the drop but, as one does, he needed a cup of tea and walked away for a minute. After nine years, the drop chose the moment Mainstone wanted tea to break. No one had ever recorded the fracture of a material such as pitch, and Mainstone desperately wanted to see what would happen at the exact moment a drop broke away from the bulk material. As the next drop was getting close in 2000, he decided to use modern technology to capture the elusive moment of fracture. He set up a camera to record the event because, darn it, he didn’t want to miss it because of another tea break. He left the camera recording and went on a trip outside of the country. His grad students emailed him saying the drop was about to go, but he was confident it would all be recorded. I remember being a grad student and the crippling fear I felt when emailing my advisor to say something wasn’t working. I would not have wanted to be Mainstone’s grad student on November 28, 2000, because the camera had malfunctioned. After 12 years, the camera had failed to catch the latest drop. You may notice that the time between drops increased between drops four and five. This is because an air conditioning unit was installed, slowing the flow of the pitch by roughly four years. Pretty impressive air conditioner.

It began to look like the drop would fall again in 2013. There was quite a bit of press coverage of the experiment and of Mainstone’s story. A live feed was set up with three cameras. Many people had a “pitch watch” window open in their web browsers. It was so close and with so many eyes on it, someone was bound to see it. The tech seemed to be working perfectly and there was triple redundancy. In an interview for Radiolab, Mainstone seemed thrilled by the prospect finally seeing the drop break. On April 24, 2014, the drop finally fell, with the world—or three cameras, at least—watching. It was caught on film for the first time eight months after John Mainstone died.

Obsidian

In the books, the terms “obsidian” and “dragonglass” are used interchangeably. Dragonglass is not something I’d try to buy on eBay, but obsidian is not terribly rare. It is unclear if dragonglass was obsidian made with dragon fire or if it was produced in a volcanic explosion. Some say it came from dragons; some say it came from the earth. Either way, it’s pretty darn cool. GRRM has assured us that there is an element of magic to dragonglass, but as we saw with Damascus and Valyrian steel, there may be a whole lot of physics in it, too.

Obsidian is formed when molten lava is cooled quickly, just as you would expect for a glass. The same magma that produces granite will produce obsidian. Both granite and obsidian are igneous rocks, meaning they are formed from cooling magma. They have roughly the same chemical composition but very different structures. The key difference between the two is the cooling time. Granite, an intrusive igneous rock, is formed under the Earth’s crust and cools very slowly, giving crystals plenty of time to form. Obsidian, however, is an extrusive igneous rock. Extrusive just means that it got spit out before forming. Obsidian is formed from the magma that leaves the Earth’s crust and granite is formed from the magma that stays inside. Because the transition from molten rock temperatures to surface temperatures causes some pretty quick cooling, obsidian forms. It usually only forms on the edge of lava flows, though, because the areas around the center have some insulating effects. It is most often black due to inclusions from the various elements in the magma and the formation of small crystals during the cooling process. Sometimes neat bubbles will form and, in the case of snowflake obsidian, sometimes the crystal pattern is visible to the naked eye.

Obsidian has been used as a weapon for thousands of years. It was highly prized in the Stone Age for its glass properties. It is one of the few naturally occurring glasses and it is by far the most abundant. Early civilizations found that when obsidian broke, it did so in a way that left a very sharp edge. For those who were less into stabbing things, it could be used to make mirrors and jewelry. Many glasses have the same useful properties, but by the time people learned to make their own glass, their civilizations had already upgraded to bronze as their material of choice for weaponry, and they were well on their way to producing steel. In 1975, an anthropologist, a materials scientist, and a geophysicist teamed up to write the definitive paper on the properties of obsidian.6 They took 28 samples of obsidian from all over the world and X-rayed them, stretched them, heated them, dipped them in acid, ran electrical currents through them, and scratched them to try and understand every last one of obsidian’s properties. They then performed the same tests on granite, Pyrex, and normal glass to measure how the obsidian held up by comparison. As was expected, the team found that obsidian had a crystal composition similar to that of granite, and it also displayed a silicon dioxide content similar to that of Pyrex. Pyrex, however, did not have the array of trace elements present in obsidian.

Reading this paper, it became clear that this was turning into a race between obsidian and Pyrex as to which could stand up to the elements better. It’s worth following the researchers’ method because I’m guessing most readers have a working understanding of how useful and strong Pyrex is. Hopefully, the comparison will give you a better understanding of how cool obsidian is. The melting point of obsidian is much higher than Pyrex’s, and it can withstand far more heat than Pyrex before softening. (Obsidian brownie pans are starting to sound pretty good.) When a glass is heated, like most other things, it expands. Obsidian expands about twice as much as Pyrex does for every degree (°C) the temperature is increased. Next, they threw Pyrex, obsidian, and window glass in hydrofluoric acid and measured how their weight changed over time to determine how much had been dissolved. Obsidian dissolved about 50% faster than Pyrex, but seeing as Pyrex barely dissolved at all, this is a really small increase. Window glass, by contrast, dissolved three times as fast as Pyrex. I’ve been talking about glasses as if they are an either/or situation—either the solid crystallizes, or it freezes into a glass. However, that’s not really true. It is possible for a glass to have some crystals within it. Obsidian is of that type. As I’ll discuss further in chapter 9, granite, and therefore obsidian, is partially composed of feldspar. In the obsidian samples they imaged, the group observed feldspar crystals scattered throughout the glassy matrix. After looking at the hardness, which varied widely between samples, it was theorized that the crystals strengthened the obsidian. Obsidian is much like the other White Walker killer in that way. Again, microstructures are giving rise to macrostructures that kill. I know that was a bit of a laundry list, but it got some of the fundamentals out of the way for those interested.

Now let’s get to the good stuff: Why does obsidian work so well as a knife, and what happens to it in the cold? Obsidian is very hard and, like anything else, hard things are also extremely brittle. Obsidian will break very easily. It’s not going to make a good sword. The way it breaks, however is quite useful. Stone weapons are time-intensive to make and easily broken. As a glass, obsidian can actually be shaped and sharpened just by breaking it. Glasses such as obsidian don’t fracture like crystalline structures. Instead, they undergo conchoidal fracture, meaning they fracture like a shell. Crystalline solids such as ice and steel like to break along specific fracture planes. Because there are a lot of fracture planes in any given solid and they might not all be going in the same direction, the breaks aren’t always clean. With an amorphous solid such as obsidian, there’s no preferred breakage direction. When glass is hit, the impact radiates out like ripples on water. If you are like me, you probably have at least one crack in your windshield from a rock on the road. Look at it carefully and you’ll see that it has a fracture pattern that looks like the ripples on the water after you throw a rock in. The molecules are sitting pretty much the same way they would in a liquid like water, so that’s not surprising. When a rock is thrown in the water, it creates a force that radiates outward, and the water reacts by moving in ripples. Similarly, when a glass encounters a force, such as a rock flying toward it from a gravel truck, it wants to move like ripples on the water, but it can’t because it’s a solid. Instead, it breaks the way it would have rippled. These fractures leave very sharp edges. Because there’s no crystal structure that needs to hang together, in some cases obsidian can cleave down to a thickness of just a few atoms. It’s this fracture pattern that makes a broken wine glass so dangerous. Obsidian obviously had many uses back when the only other option was granite, but its unique fracture properties are still being used today. A small number of surgeons are now using scalpels made with obsidian blades. Obsidian can be much sharper than the normal steel scalpels because of the conchoidal fracture. Because the blades are so much sharper than steel, surgeons feel they lead to faster recovery. There are a few huge downsides that mean these blades most likely won’t be widely used. First, the blades are so sharp that you wouldn’t feel a cut from the blade unless it was disturbed by something else, such as water. If a surgeon accidentally cuts their own hand during a procedure, it’s best to know as soon as it happens. Second, the blade cuts through skin so easily that surgeons would need to retrain themselves to get a feel for how these new blades work so they don’t cut deeper than they’d intended. Retraining muscle memory is not an easy thing to do. Finally, obsidian is very hard, and with hardness comes brittleness. Obsidian blades are great for cutting skin straight on, but if the surgeon were to knock the blade against something else from the side, it would break. This isn’t a big deal on the scale of something like an arrowhead, but surgeons need to know when their tools have been compromised.

Of obsidian’s properties, probably the most important one to Jon, Sam, and everyone else about to come face-to-face with the army of the dead is how it functions at low temperatures. Well, in terms of strength, it’s not exactly doing great at room temperature. It’s hard and it fractures pretty easily. I was not able to find studies on the strength of obsidian in extreme cold, but I was able to find a paper on how crown glass, made with SiO₂ and B₂O₃ (boron trioxide), behaves at low temperatures.7 In 1957, three years after Parnell’s third pitch drop fell, Kropschot and Mikesell ran some tests on how much energy was required to break the glass, first at room temperature and again after it had been exposed to liquid nitrogen (−196°C). They showed that this type of glass gets stronger the colder it gets. The duo doesn’t identify a mechanism for why this happened; they merely reported that it did, in fact, happen.

Sam versus a White Walker, Take Two

At the end of season 7, we watched an army of wights and White Walkers make their way into Westeros. As I said in my chapter on zombies (chapter 4), the best chance a random peasant from the North has is to get the hell off the road and hide out. That said, Jon’s people are coming back from Dragonstone armed to the teeth with obsidian. There is no definitive answer as to whether dragonglass came from the mountains of Valyria or whether it was forged by dragons, but I’d like to assume it was dragons. In the next chapter, I’ll talk about what happens when a dragon goes up against granite. (Spoiler: the granite doesn’t win.) Dragon fire is hot enough to melt sand and stone (I promise I’ll tell you why if you keep reading), and there is a huge cache of dragonglass under Dragonstone, right where a bunch of dragons used to live. Given that narrative, I’m going to assume that dragonglass is made by dragons melting granite, which has the same chemical composition as obsidian, and then letting it cool quickly. The only other weapon that was able to kill a White Walker was one forged with dragon fire. To me, it makes sense that dragonglass creation involves dragons.

Armed with dragonglass, how would the army of Westeros hold up against the army of the dead? That’s a hard question to answer. Dragonglass has a lot going for it. Unlike steel, it strengthens when it gets cold. It’s still quite brittle and will fracture easily, but when it fractures, it does so in a way that keeps it sharp. Unlike steel, if it shattered while inside a White Walker it would still be quite deadly. I had someone ask me why normal swords couldn’t just be covered in dragonglass, thus making the ultimate weapon. Unfortunately, that wouldn’t work: the obsidian would probably fracture off quickly; it’s next to impossible to bind glass to steel; and it would shatter if a White Walker were struck with the actual blade, leaving the hero defenseless. I think the biggest challenge would be making sure there’s enough dragonglass weapons for everyone to quickly grab another in case theirs shatters. Surgeons have had a hard time adapting to the new obsidian blades because they were balanced differently and so much sharper than their normal scalpel, and I could see trained swordsmen having the same issue with dragonglass. Obsidian is lighter, so an obsidian sword would be balanced differently than a normal steel sword. It makes a much better knife or spear than a sword, anyway, so some weapons training would certainly be required. There could potentially be more collateral damage as well if people were to slice themselves with their own dragonglass by accident and not realize it until much later. If a surgeon can cut themselves without feeling it during surgery, what might fighters do to themselves in the adrenaline-fueled heat of battle? At the end of the day (or the beginning of the Long Night, depending on your point of view), the physics of dragonglass clearly shows that it behaves much better when battling a White Walker than normal steel. If the people of Westeros lose this war, physics had nothing to do with it. As for training with new weapons, the aim is always the same: stick them with the pointy end.