Re: Casting Flux?
Sawdust for me as well. Stirred in with a hardwood dowel.
As far as sorting goes, I'm with Rusty. The almost pure stuk-ons are easy it's the zinc that can be a pain. It takes a lot more heat to melt zinc, steel or aluminum (which I've never seen). Just dump them in and scrape off the garbage that floats. But watch your temp, 650 ° is good.