Glor, I've read about, and if you'll recall from the prologue, the liquid dust forms together to create incredibly powerful shades. I believe its power originates from Necro, and that's how it replenishes itself. Kind of like a power house on the outside of Necro so the shades can exist off their land. This also leads me to the conclusion that when Jack Willow came to the House, the shades came upon him and sucked him into oblivion/necro, which he may have known and sought since he once combatted with Necro so fiercely, and may have wanted to return to that.