To craft the Dao of Pow, a dark and light shard is required from a dark and light mummy, which spawns on corrupted and hallowed deserts respectively. Unfortunately it seems that in my world there are only natural hallowed deserts, which means that I've only managed to obtain light shards.
The Terraria Wiki article for mummies indicates that it is relatively easy to create the biome artificially, but lacks any significant details on how to do so. I've experimented myself with small amounts of ebonsand quarantined in forest biomes, but so far no dark mummies have spawned. What is the minimum amount of ebonsand needed for dark mummies to spawn, and how can I do this without corrupting a normal desert?