Minecraft wiki entry for Elytra, associated text: Each repair on the anvil will also increase the prior work penalty for the Elytra, making every subsequent repair increasingly expensive, with an upper limit where repairs are no longer allowed because they are "too expensive". However, the prior work penalty can be reset to 0 for an enchanted elytra pair when it is disenchanted on a grindstone (by adding nothing to it). Unenchanted elytra cannot be used on the grindstone alone.