Board Thread:Help Desk/@comment-186.81.186.236-20130421024305/@comment-7962494-20130421215548

You only need 4 Demonite Ore  to make 1 Demonite Bar. You can smelt them at a Furnace.

If the recipe is not showing up, talk to the Guide and show him the ore while near a furnace and you should be able to craft it.