FumeFX/rendering/materials: making flames invisible at source


i’m working on compositing some fire onto a live action vehicle for a film. i’ve gotten a pretty good look for my fire that i’m happy with and now i just need to render it as realistically as possible but i’m having trouble with creating a material or curve that get’s me the right look. the fire is supposed to look close to that created by a molotov cocktail hitting a vehicle’s windshield so i want to see a virtually invisible clear liquid that is burning with flames from the area that was hit with the fuel. the only big problem i’m having with the look of my fire is that the source of the fire sort of glows a bright orange where i want it to be invisible but have flames lapping up from only those areas that have fuel on them.

here’s a frame grab of the fire roughly composited into the shot.

i wish i could post it in motion, it does look better that way but clearly it looks too much like an electric orange gel is producing the flames not a clear splash of gasoline on the surface of glass.

take this real world example, the torch is covered in fuel and we see the flames coming off the source but the source itself isn’t a glowing orange surface, it’s invisible at the surface then brightens as it rises.

i’m using an object based emitter and emitting only from the areas that i’ve painted white as a texture that looks like splattered or running gasoline that hit the surface. if i could just have it so that the flames don’t appear until they’re just beyond the surface of their emitter that would be great. i tried using the fade edges near objects controlls which i didn’t totally understand but had no success.

i know this look is possible, i’ve seen something like it here: https://vimeo.com/44426733

in the video, the fire on the left looks like a burning puddle of gasoline and while it’s still slightly visible, it doesn’t look like a glowing blob of orange lava that fire is coming off of. the flames gather from the surface invisibly and become visible as they condense and rise.

so how can i make my fire invisible until it’s a bit taller into it’s flames, a bit further from it’s emitter? i’ve spent a lot of time working with gradient and or opacity curves, trying the extremes of just thin slivers of color and thin spikes of opacity to find what areas control which and i can’t seem to figure it out. how can i hide my emitter shape? i just want flames in that region, i don’t want to see the emitter glowing!

anyone have any helpful suggestions for me on how to do this or any other tips on creating materials for my flames?


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