Minecraft wiki entry for Smelting, associated text: When smelting items, it's best to choose a fuel that is most suitable for how much you are smelting, so that you can use up as few resources as possible. In these examples, the process is making green dye, but this works for any item. For slabs, wooden planks, and saplings, oak is used, but it does not matter what type of tree the item came from. Also, you can replace one of the slabs with a stick or sapling when burning slabs. Two slabs can be replaced with one of the following items or vice versa: