[Excaliber]

Somewhere on this site is a little blurb, likely posted by one of the brothers K, about how they weld aluminum. It's a real art. Something about sooting the area up with the torch (heavy on the gas, less oxygen) and then just when that soot begins to burn away the temperature is "just right".

Having done a lot of copper brazing myself the techique is similiar. You do enough of it and you can almost "feel" or "sense" when the temp is right. It's an art.