Over at the official Making Game of Thrones production blog, Cat Taylor shares a scene from early in the fourth season filming, when the production put together some tests to simulate visual effects for the dragon flames that will be seen this season. Here’s an excerpt, right from the end:
As the dragons grow and start to test their power, their fire breathing will get stronger and more powerful. The Dragons are legend for a reason and this season we will get a hint of why. The final tally, 22 canisters and 400 litres of gas – all for just one day in Essos.
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via Game of Thrones: News http://www.westeros.org/GoT/News/Entry/Making_Game_of_Thrones_Dragons_Breath