Brass

Welding brass is tricky because the zinc in the alloy evaporates quickly when heated. You see it as white smoke, and the material becomes porous and loses strength. So you need to apply heat briefly and precisely, preferably with a process that focuses the energy well. Keep heat input as low as possible and don't let the part glow, otherwise you'll get cracks or distortion. Cleanliness is key; the workpiece must be grease-free, and for most workshop work, TIG welding is best.