Lead burning is a procedure used to join lead alloy pieces together. When done properly, the joint will be rigid, strong, homogeneous and free of pinholes. It takes a little practice to become adept at lead burning and it is best to practice on scrap pieces first.
A fuel is used along with oxygen in a special torch and the joints are actually flowed together. Unlike welding, lead burning uses a very small flame. A flux is not needed and the flame is concentrated in a small spot to avoid overheating adjacent areas. The flame should be adjusted so that it is neutral, or just slightly reducing. Never use an oxidizing flame as this will greatly reduce the strength of the joint. The torch is moved slowly and the flames blue inner core should just touch the joints surface. Control of the flame type and its size are both important. A typical oxygen pressure of 10 lbs. at the regulator is used.
The lead burning torch should be small and lightweight; it uses # 0 and # 00 tips. The best fuel to use is natural gas as it is the cleanest burning and provides the best results. The next best fuel is propane and acetylene is the last choice as it is the dirtiest burning and produces the weakest joints.
Lead burning is done with the two surfaces touching and needle nosed vice grips are used to hold them tightly together. It is best to do lead burning in a horizontal position if at all possible. Rollers are used to support larger anodes during the fabrication and the lead burning process. Should vertical lead burning be needed, its best to work from the bottom upwards.
The technique that provides the strongest joint is to use a slow and smooth pattern; unlike welding a swirling motion is not used. The joint is first burned together and a filler rod is added later if additional material is needed.
Burning new cast lead is fairly easy to learn. Burning a lead alloy that has already been used for plating, such as extending an anode length is much more difficult. The old area must first be thoroughly scraped and wire brushed to expose fresh lead alloy or the lead will not melt and flow properly. Do not blast lead alloy to clean them as this imbeds the media into the alloy causing further difficulties.