I didn't mean to suggest you could ever get it all out.
My post was based on normal old time stick on wheel weights where they were close to pure lead.
The impurities will float to top without fluxing, but fluxing does help.
But because tin and antimony melt at higher temps than lead and are lighter, these will over time with and without fluxing float to the top.
Will you ever get them all out of a pot, ,,,,,,,,,no.
But you can skim off quite a bit.
The only time you should have lead oxidizing and forming a crust / skim is if you are not smelting at the correct temperature. Use a thermometer.
Good clean pure soft lead at correct temp, should have very little skimming.
Of couse there will always be a very fine discolored skim. That is usually just the lead it self that has cooled on the surface of the pot.
The nastier stuff you want out is thick heavier and more crusty and will solidify almost instantly when lifted even a fraction of an inch from the surface.
But will you ever get a pure lead smelt at home from a mixed alloy? no.