I don't know guys, maybe I live right, but I haven't fluxed lead but once in my life and haven't found any lead that's bad enough to do it since. The act of lead heating and cooling causes some hastened oxidation but I skim the pot every time I add lead or fire the pot up. No biggie, no fluxing. I have a propane gas stove top that I took out of a permanent ice shack years ago that I held onto for camping. I set this out in the driveway with a cast iron pan on it and melt all the lead I plan to cast with in this, skim the molten lead and then pour my ingots.
Unless you are buying ingots or "new" plumbers lead, you'll need to skim the lead you're heating regardless. Lead is heavy and when melted anything that isn't good in it will float to the top and is easily skimmed off with a simple spoon. Using wax and other agents to flux? Do you really think they can be "stirred into" the hot lead, as in mixed in? Sure as heck not well enough to do much good. I dump my pots every few times they get heated and used so that I can clean the tub. I use a narrow wire brush and steel wool for this and I remove the rust deposits that form in there and both bottom-pour and hot pots are trouble free. If you're using an agent to flux a bottom-pour, maybe empty the thing and give it a good cleaning in more in order.
I've been casting jigs since 1964 and have used every conceivable blend of lead imaginable and haven't ever seen the "need" to go beyond skimming. The only hard and fast rule I use in the jigs is this: the smaller the jig, the purer the lead. Sinkers see wheel-weight lead. The couple of jigging spoon molds I use see wheel-weight lead. The molds with the brass body inserts to make the shad and jigging blade baits see wheel-weight lead. Spin-casting equipment can handle alloys if the metal is hot enough....and I haven't used my spin caster for years, much preferring to hand pour. Basically every "jig" I cast sees pure lead. I keep the alloyed lead and pure lead in their own hot pots.
Something else you'll learn about even pure lead is that it can "work harden", or start to act like some harder alloys, thru repeated heatings to very high temperatures. This doesn't happen often. Lead is lead is lead is lead. If your lead is starting to get funky every time you go to use it, clean your heating equipment out. If the molds don't fill right, heat the molds with some hook-less, dummy pours to get heat into them. Pour a couple of full molds without hooks and let the hot lead stay in the mold for a half a minute.
