Think back to our question from ghandirocks about whether or not there could ever be a black flame. We brought up Planck’s Law to try and figure this out, which describes the light (or EMR) given off by something hot. Flame colors can have different explanations, but the most common is that flames are hot and have particles in them.
The Clear Science Staff fired up our computers and plotted the emissive power from Planck’s Law (qλ) depending on the temperature of the hot thing. It’s a weird-shaped function you see above, which tends to have a maximum (and it’s a log scale) in the visible light region between what we call ‘violet’ and ‘red.’ You might already know this: that hotter things tend to burn blue and colder things burn red.
For a flame not to emit any visible light, it just needs to be really cold, like 500 K. This is 227 °C or 440 °F, which might be a slightly high oven temperature when you’re cooking. Most flames burn around 2000-3000 °C, so that would be a very cold flame. Remember though, this is just to make the flame colorless. For it to be BLACK it would have to absorb light instead of emitting it. So if there were lots of particles, like a very sooty flame, and it were also cold like this, then yes you could think of it as a black flame.