Bronze

Made in a small fire pit, deck grill with a stone ingot, or in a primitive smelting furnace or smelting furnace^* using bellows.

Could be used as a alternative to iron for making some weapons and tools. However with the absence of phosphorus in the game; an ingredient needed to smelt bronze, it is currently impossible to make.

^*: Note that the smelting furnace can't be made without iron.