In our Chemistry labs at school, we have an infamous demo we love to do, called the ‘Whoosh Bottle.’ A small quantity of Ethanol is placed in a big water cooler bottle, swilled around the inside and then, with lab coats, safety specs on and safety screens in place, the top of the bottle is lit.
Notice how the flame is blue to begin with, as ethanol is burning cleanly with oxygen, but a yellow colour then dominates as incomplete combustion occurs. Basically the oxygen is getting used up and Carbon particles are being produced which glow yellow in the flame. Later on, as the pressure inside changes the top flame diminishes and more air is drawn into the bottle, causing a ‘glugging’ effect and a change back to a blue flame temporarily. I don’t think I would have noted this without using slow motion!
Again, this video was filmed on a Raspberry Pi with a Pi Camera. Shutter speed was 90fps. I then converted it to an MP4 file on the Pi, before putting it into Serif Movieplus for editing. The central video is slowed even more to 1/30th of original time.