@SeanKeplinger … really late reply here, but ‘cold casting’ is usually mixing metal powders into a resin of some sort (epoxy, urethane, even polyester). You never really need to fire it, just polish it up and it can look like solid metal. Won’t be as strong obviously.
I find copper and bronze powder on E-bay or amazon (300 grain or so), and use it in 2-part T-88 epoxy for filling engraving lines or even worm holes and flaws in woodworking.