The easy trick to refining cupels is simple carbon reduction. Crush the cupels, mix with smashed charcoal in roughly equal volume, then put in a closed-up clay pot in the furnace and let it burn for a while. The lead will reduce out in metallic form.Are you a lead refiner? Seriously, if you are, most refiners (even the ones who don't admit it) discard their used cupels in the trash. Truth is they are hazardous waste because they do fail TCLP testing. (which the only client who ever wanted to discard them properly tested for at my suggestion) But they average 40% by weight lead. I could get you lots of samples!!!!!
That's one reason why I'm building a larger brick furnace. I can use wood and old railway coal; which I get from an old abandoned railway near me has TONS of PA anthracite coal bit lying around, which has been washed clean for nearly 100 years. It burns smokeless with a bright blue-white flame.
I can take care of all my waste at almost no cost. Solutions full of toxic salts can be evaporated down to crystals or hard cake forms (depending on the salts present). I can even glass them if I can find a cast iron pot to melt the salts into the plentiful quartz sand in my area, and the mounds of potash left over from burning wood in the wood stove we're installing at home. The vitrified salts will be inert, chemically bound in the glass.