Liquid copper can be poured into a Ceramic Mold to make unshaped copper. Once the unshaped copper is no longer liquid temperature, it can be placed in the crafting grid to create a copper ingot. The empty mold will be returned to the inventory; although there is a chance of it breaking and being lost.
Creating an ingot will only work if the metal is in a solid state. The temperature will be carried over from the unshaped ingot temperature.
Casting & Smithing
Right click a liquid Unshaped Copper to open the casting UI.
Place the ingot in the leftmost slot and your Ceramic Tool/Weapon Mold in the center slot. The arrow will progress and you will end up with your filled tool/weapon mold on the right, and if it didn't break, the empty ceramic mold on the left.
Place the filled mold in a crafting grid to remove the head. The empty mold will be lost in the process.