LP, your base material looks exactly like the roof vent and flashing lead I've been fortunate to get occasionally - some of the softest lead I've used. Usually, there is some tin solder adhered to the sheeting which IMO improves the lead and gives the melt a shiny surface, as opposed to the darker skin of purish lead.
Simply stated and you probably figgered - one can flux too much. Judging by the appearance of your scrap and the amount of floating residue on the initial melt, a single fluxing after first skim would have been sufficient.
After having processed at least 1,000#s of roofing lead, never had your experience.
Firstly, I would guess that your melt heat was too high. The hotter the temp, the more oxide/carbonate slag will form. Secondly, wax flux doesn't burn off completely, and part of the floating residue appears to contain unburnt carbon + possibly wax impurities. I would guess that you considered the continual formation of slag during repeated fluxing evidence of impurities in the lead that required further fluxing, when in fact the melt was being gradually depleted due to chemical compounding of the metallic lead into slag + the affinity of this slag waste to physically adhere more metallic lead when skimmed.
I agree that you might be able to extract metallic lead from the slag, tho probably way less than your starting melt. By saving & repeated heating/fluxing/straining slag in a small open tilt pour pot(long handle really helps) it's possible to extract most of the useable adhered lead leaving only powdery non-metallic dross as terminal waste. If anyone wants step by step of this process I can post it. Main thing to note about the reclamation process is that after pouring out the liquid metal the remaining dross should be cooled till any remaining liquid lead has solidified. Otherwise, the steel mesh strainer used to separate terminal powder will get messed up.
