Not sure how you evaporate lead other than, possibly, with infeasible amounts of heat. I've seen beads of metallic lead, not lead ash, in and removed from the annulus of plugs pulled from the engine of the local flight school aircraft. For that to form conditions in the cylinder have to be 'reducing' ie. not oxidising, so maybe the engine was running overly rich.
No help with the OP's mag drop question, just commenting on A and C's lead fouling post.