Just dry graphite. I take a pencil and shade-in the top of the mold and the bottom of the sprue plate with it before I preheat the mold. You can quickly add more when casting if needed and it won't migrate to the cavities. You can also use the pencil tip to scrub off any small specks of lead you might smear while casting, as you are still casting, and the mold won't have time to cool down.