There is not a single flux stone in the entire world. I could not make this up if I tried. Steel, the tried and true metal of dwarven kind, does not exist.
So you can get a few bars every year, that's not enough to work with, right? Wrong. Dwarf forge and smelter pseudoscience is so advanced that they can make chain leggings with one bar of steel, melt them back down, and wind up with a bar and a half of steel. Not that you can do much with half a bar, but the next time you run the reaction the smelter will spit two bars back out.
Dear armok, is this true??? I hope it is, not for exploity/infinite-metal purposes, but just for ease of armorsmith training. And was this true in .31.25?
I don't know if it was true in .31.25, but it's true now. There's a bug report on it. I've only personally tested axes though, I was more concerned with getting a legendary weaponsmith and was willing to endure the slower return rate to get it.
For armorsmith training, leggings are great, and for weaponsmiths battle axes are good - both give 3/2 bars when smelted. For metal multiplication, you want coins - look on the wiki page for exploits under Adamantine factory or something like that.