Forges can create bloom and turn coins into metal bars, so why not turn a metal-product back into metal bars/nuggets. Reforging would create a 1 or more metal bars/nuggets (depending on what/how much was used to create it), with a reduced quality of the metal-product. i admit i don't grasp the quality formula, so i am going to leave that to those wiser than myself.
also, any non-metal used to create the product is lost during reforging.