As they prepare for battle, the armies at Winterfell are spending a lot of time making dragonglass weapons. Here’s a look back at why this is so important.
Dragonglass and Valyrian steel are the only substances that can kill White Walkers. Dragonglass is a type of volcanic glass, also known as obsidian. Valyrians once called it “frozen fire.” Although folklore holds that dragonglass is made by dragons, Maesters believe it is just a type of volcanic rock.
It was also used by the Children of the Forest to create White Walkers. This is likely why it can also kill them. The dragonglass somehow introduced a magic into the humans of old that turned them into White Walkers. Plunging that dragonglass back into them must undo that magic. Here’s the scene from Season 6 when we learned how White Walkers were created:
Sam found a cache of dragonglass at the Fist of the First Men in Season 2. In Season 3, he accidentally discovered that it kills White Walkers. He gives a dragonglass dagger to Bran and Meera, along with dragonglass arrowheads.
In Season 5, Stannis told Sam that there was dragonglass in Dragonstone. In Season 6, we learned that Benjen was stabbed by a White Walker and was partially on his way to turning into a wight. But the Children of the Forest found him and inserted dragonglass into his heart to stop him from turning. I’ve got to wonder if something like this might happen again in Season 7.
We’ve also learned that Targaryens used to adorn their weapons with dragonglass.
We know a little more about dragonglass from the books, but because the books and the show have diverged, it’s unclear how much of the books’ information is actually relevant. The Game of Thrones Wikia explains that dragonglass is useless against wights. Melisandre says this is because wights are still just dead flesh, while White Walkers (the Others) are something more. Likely this means Viserion is also something more, as he was created in a similar way to the White Walkers when the Night King touched him and his eyes turned blue. So dragonglass could be fatal to him.
Dragonglass is the main ingredient of all the weapons that Gendry and the others are making as they prepare for their great battle.