Dragon Magazine #295, p39... It allows you to create metal items more efficiently.
"Normal metal items can be constructed for 5% less than the normal cost described in the Player's Handbook; this includes Masterwork items. Magic Itemscreated with the Lava Forge are effected, but only the cost of the base item (such as a masterwork longsword) is effected; the cost of enhancing the item is not reduced."
To make a Lava Forge:
CL15
Prerequisites: Craft Wonderous Item, Flame Strike or Delayed Blast Fireball.
Market Price: 15,000gp