The neutral flame is the flame in which the amount of oxygen is precisely enough for burning, and neither oxidation nor reduction occurs. A flame with a good balance of oxygen is clear blue. The reducing and neutral flames are useful in soldering and annealing.
Neutral Welding Flame. The neutral flame has a one-to-one ratio of acetylene and oxygen. It obtains additional oxygen from the air and provides complete combustion. It is generally preferred for welding.