It is actually the lead, while in the pot, that turns this purple/blue. I don't have one of the Lee Melting pots/pourers yet, but use a normal small Stainless Steel pot on a gas burner. I use a ladle to pour the jigs, thus actually getting the odd color lead into the molds. I normally do the powder painting within a week or two. I will try the vinegar, how long does it need to stay in there?