I think that if you have a botch piece of slag as the result of trying to craft something that there should be some reduction in both weight and amount of metal that remains. This would depend strongly on what you are trying to craft. Something small like a copper lure, and you botch would not give you anything worth salvaging. Something larger should, though if what you were crafting required three ingots and you botched the craft, when you take it to the recycler, you would get two ingots back. The recycler giving half of the metal the you used back. A object that requires only a single ingot and you botched, would give you nothing, the slag would be consumed by the recycler.