If the lead isn't shiny then it has oxides that form a black coating on the surface, or white powder if really oxidized. But just dealing with that black oxide layer by fluxing can help drive the oxides and any alloys back into the melt as opposed to skimming them off. As well as help pull any debris out. Handful of clean sawdust or wood shaving rodent bedding can only help, and certainly do no harm. Avoid sawdust that contains plywood, particle board, or treated wood sawdust. E.g. big box home improvement stores sawdust. Best stuff I have used is shavings from a planer, followed by clean lumber sawdust, and then wood chips from a chain saw.
X-ray sheeting, or blocks are great but I would expect to flux even clean ingots added to a batch if they have sat for a couple or few years in the garage. Worst stuff I ever dealt with was glued to wall using a notched trowel, so one side was covered in glue. When that smoke stack ignited it was pretty impressive (looked sort of like a rocket engine firing straight up) but there was a lot of sheet rock and assorted debris in the melt.
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