When heating non-ferrous metals, oxides form on the surface and prevent the flow of solder and just generally make a mess. This is because 3 things are present; metal, oxygen and heat. Eliminate any one of those 3 things and oxides won’t form (or at least they’ll form much more slowly). An oxide-inhibitor (anti-ox) is a coating that prevents oxygen from reaching the metal just long enough for the solder to flow. You can buy commercial inhibitors, but I make my own by mixing about 2T. of boric acid with about 1/2 c. of denatured alcohol, which I then keep in a covered container. Before soldering or annealing metal, especially if using copper, I dip it into the anti-ox and then burn it off. The alcohol is mostly a carrier to make the boric acid form a thin coating on the metal, thereby preventing oxygen from reaching it.
Boric acid is available at pharmacies (you may have to ask for it at the counter) and denatured alcohol is available at hardware and home stores.
Burning off the oxide-inhibitor is such a quickie little job that it’s kind a pain to light the “big torch” to ignite the inhibitor, and then to turn it right back off while you set up for the actual soldering operation. While most butane torches take 2 hands to light, I use a MicroTorch or other 1-handed torch to burn off the oxide-inhibitor. It’s really simple to light and far safer than keeping an alcohol lamp burning. I even use mine to light my pellet stove!