The Infernal Furnace is a magical fuel-free furnace added in Thaumcraft 3.
You must research it, and it requires the Unified Thaumic Field Theory. It is a 3x3x3 structure made with 12 obsidian, 12 nether brick, 1 iron bar, and a bucket of lava. After building the structure, you must then right click it with a wand to create the furnace. It costs 100 vis to create it. Before you build it, you have to unlock it. To unlock it you need the following essences: Animus (Soul, Spirit), Imperito (Control, Command, Dominate), Saxum (Stone, Rock), Ignus (Fire, Heat, Burn), Praecantatio (Magic, Sorcery), and Vinculum (Bind, Imprison, Trap).
The completed furnace has an opening on its top where items are thrown in to be smelted. These items can be stacked and may be of varying types; they will be processed in the same order they arrived. If the furnace receives an item which cannot be cooked or smelted, that item is destroyed. Valid items take a few seconds to cook before the result is ejected out the front of the oven (along with the XP the item normally gives). As a bonus, the furnace has a chance to spit out extra nuggets when smelting ores and cooking meat. This is the only way to get meat nuggets or Quicksilver Drops.
If you break a block that is part of the furnace after using a wand on it, it will spawn a Blaze. In order to restore the furnace to working condition, you must replace the missing blocks from the structure and then refill the lava in the center as it's consumed when the blaze spawns. After doing so simply wave your wand at it again to restore it.
Heres a video that shows you how the infernal furnace works http://www.youtube.com/watch?v=OBXn9xqYN5c
Due to it needing lava to create it is nearly impossible to create on servers which ban lava use.
To get around this it is advisable to find a lava lake or other natural lava block and build using this as the block in the structure.
Smelting dusts of an ore doesn't produce extra nuggets, but still grants experience points.