In a forge, the fire acts as a heat source that drives the metal to liquid state. A hot charcoal in the forge will make all the better as it absorbs some of its heat from the fire. The amount of heat and quantity of charcoal used will depend on how thick you want your product to be
You can also melt metals in an oven by using a kiln. There are several types of kilns available in the market but always remember to keep an eye on their temperature so that they don't burn your product and cause it to crack or split.
melt metal in a forge