Her eyes were the blue of a very hot flame.
I think he's trying to make some sort of very hot flame.
Over the hot flame his hands were trembling and cold with fear.
A fire that would flame hot and high, then die away to nothing but ash.
The type of glass to use next to the hot flame was a problem eventually solved.
This is why the very hot flames emit blue light.
The mixture of gas and air produces a very hot flame.
He could reach into the hottest flames and not get burned.
It also makes a very hot flame that can melt iron.
And then, with a final hiss of protest, the hot flames suddenly died away.