Sometimes when I'm using a bag mold and empty the ladle on it, those strands of lead that overflow will not permit the opening of the mold. So they are simply broken off and threw back in the molten lead. Some of those strands snap right off. Some have to be bent back and forth several times to get them to break off. Is that an indication of the purity of the lead or does it indicate something else?
I dunno for sure. "Pure" lead shouldn't be brittle and if it is then I'd think it's not "pure" and is either an alloy and/or has contaminants. Melting lead or lead alloy (tin and or antimony) all needs to have the dross removed continually, as well as stirred often.