The Disenchanter is a deceptively simple device for recovering enchantments from items. Use it by itself, and the first enchantment will be returned and the item destroyed. Use one of the Catalysts however and you will get a different set of enchantments back. Some of them will even preserve the item in the process!

To use the Disenchanter, craft one, place it down and right-click to open its interface. In the leftmost slot you can put the item you want to be disenchanted. The rightmost slot takes books onto which the enchantments are transferred. The center slot is for the Catalysts, which are outlined in the following section. As mentioned above, you can also use the Disenchanter without having anything in that slot.

Amethyst Shard: Recovers the first enchantment and preserves the item
Diamond: Recovers two random enchantments and the first one
Emerald: Recovers two random enchantments
Ender Pearl: Recovers one random enchantment. Here, the item is also preserved but will take 500 durability damage
Experience Bottle: Recovers all enchantments that are at the same level as the highest one present
Heart Of The Sea: Recovers all enchantments but reduces them by one level
Nether Star: Recovers all enchantments and preserves the item