I understand the idea behind leaving a film of some sort of flux or reduction agent on top of a bottom-pour setup, but curious on some of the fluxing processes ladle-pourers use. I smelt all Rotometals and honestly, not even sure I need to do much cleanup there, if at all. I just want to ensure the blend I'm smelting is well done and ready for the casting pot. It goes into the Lee furnace clean.
My usual method is to come to temp (94-3-3, 725Fish), drop a tablespoon or so of sawdust, allow to carbonize, stir it well in, making sure to scrape the sides of the pot thoroughly, skim completely, and start casting. At some point during a casting session, which I usually do in 2 hour increments, I'll repeat the sawdust to reduce the oxidized metal back in.
That obviously leaves a growing oxidized skin that I will reduce at inexact times. I think it was Larry Gibson who said you don't need to worry about the oxidized skin somehow being preferential oxidation (i.e., over time you are losing a greater and greater amount of tin, so you are changing your alloy as you cast) so I've been less concerned about when I will re-reduce. But perhaps I misunderstood him or am missing something critical here, so getting your thoughts.
On my Accurate 46-405VG I am keeping only bullets that look good visually, 390.0-391.9 grains.