I'm going to assume that they were mine.
I'd clip them to remove only the gold buttons, and what little wire and insulation came with them. I'd then incinerate them to eliminate traces of insulation, screen them to get rid of the ash (which would go in my waste materials for future firing in a furnace because you're likely to lose a little gold here), and use the buttons and what little wire that came with them as the added metal for inquartation. That's the point. If you have no need for inquartation, it's of no value for you. The objective here is to dissolve them only once, but for more than one reason. If you melt them with other junk, you gain nothing. You're better off to put them directly in acid, after degreasing.
Unless you have a melting furnace that can sustain high temperature for a prolonged period of time, and use a reducing flux, screwing around with slags will end up killing one hell of a lot of your time, and you're probably going to be leaving the bulk of the values behind instead of recovering them. The metals in slag must have a reason to collect and form a button.
A flux that will be good for recovering values will be very hard on crucibles. It must liquefy everything it contacts, and must be thin and fluid, to allow the prills to agglomerate. If you mess with thick, pasty flux, and don't provide a reducer, you're really wasting your time. Fluorspar is a wonder thing to thin your slag, but it is very aggressive and dissolves most everything in its path. Even alumina.
Want to talk about what you're doing? I'm at a loss to understand where the slag you mentioned came from.
Harold