It's been a while since I've made a batch of ingots, but I heard of using sawdust or stirring with a wooden dowel to create carbon, which pushes the alloys back down into the lead. Supposedly, using wax as a flux will bring the alloys to the surface along with the impurities and steel clips from COWW which you'd skim off, leaving you with a softer lead. And what about Marvelux? Any thoughts?