My current fort has a very standard set up metalworking room. Magma forge, Slag Pit, Magma Smelter and a corridor leading to a bar stockpile.
While messing around trying to set up a whip vine mill I get the message that one of my smiths has gone moody. A quick zoom and i see him running to his forge and starting to gather materials as usual and he quickly gets to work.
Fast forward until a little while after, And he has created a mechanized axe thrower, But something is not quite right. When he started gathering he immediately grabbed the nearest bar to use as the base metal. Can you guess what bar just so happened to be closest? A bar of slag. He used SLAG to make his super artifact doomweapon. I can just imagine a soldier holding this long, crusty black object and firing at a goblin only for the handle to disintegrate and cover his shirt in black dust. Clearly Mr Smithy will pave the way for a new age of cost-effective dwarven weaponsmithing.