Cat Taylor has updated the Game of Thrones production blog with a detailed description about Stannis Baratheon’s flaming sword.

While Game of Thrones has completed shooting season 3, there’s still a lot of post-production going on. And in a new production blog entry, Taylor writes about how one of her favourite special effects has been created:

While chatting with the SFX team, I managed to wrangle some information on how one of my favorite effects of the season came to be: The Sword of Fire.

There were, it turns out, actually two swords – one that would burn for an actual fight sequence, and another that has the ability to bleed and ignite itself.

The fight-sequence sword is a real sword that the workshop team milled with a number of channels, each one stuffed with a dura-blanket material. The flame retardant fiber is then soaked in IPA (isopropyl alcohol). This was then covered in another layer of material to make the blade look uniform and sword-like again. Because of the length of the sequence, the flame has to last (and burn strong) for at least 3 minutes, which was something of a challenge, as the fuel burned off so quickly.

The second sword had blood inside the blade and could be ignited. The sword itself split into two pieces, and the inside was filled with a series of small, sealed channels. Some were filled with gas, the rest with fake blood – that way, when the blade was drawn across any surface, skin or otherwise, hitting a button on the hilt of the blade would release blood through tiny holes down the side, making it appear as if blood was welling up from a cut.

There was a tiny pilot light, which you could never see on the blade, but when a button was pressed and the gas released down the channels, the sword would burst into flames. You could not use this for any contact during a fight scene, though, as the mechanism inside is too delicate to withstand the impact, and with the blood and gas being supplied into the blade, it would be unsafe to use for stunts.

Game of Thrones will begin airing on March 31, 2013!