They change ingots, so you take 3 gold ingots, drop it into the cauldron, and out pops 1 agapite, then 3 agapite to 1 verite, and 3 verite to 1 valorite. All told you can convert 27 gold ingots into 1 valorite ingot, if you're so inclined.
I wonder if the valorite maps don't become more useful if you do all the mining thereof with gargoyle pickaxes. If you get 300 'swings' with a garg pickaxe, you should get 5-7 Valorite elementals too, with 25 ore each. Well, per UOGuide, Valorite pickaxes don't work, so that idea is out.
I totally agree with
@BeaIank that 6 hours in Blackthorn's dungeon + another 6 hours of void pool is probably the best yield.
You can also do quite well if you use a Gargoyle's pickaxe + Prospectors tool to mine.