ghost dust

He barked out an incredulous little laugh. “No, you hear me out, shade. No means ‘no.’ It isn’t happening. It isn’t ever going to happen. I said no!” And then he slammed the door to the next room in my face.
“Dammit, Morty,” I snarled, and braced myself for the plunge through his door after him.
“Dresden, st—!” Sir Stuart said.
Too late. I slammed my nose and face into the door and fell backward onto my ass like a perfect idiot. My face began to throb immediately, swelling with pain that felt precisely normal, identical to that of any dummy who walked into a solid oak door.
“—op,” Sir Stuart finished. He sighed, and offered me a hand up. I took it and he hauled me to my feet. “Ghost dust mixed into the paint inside the room,” he explained. “No spirit can pass through it.”
“I’m familiar with it,” I muttered, and felt annoyed that I hadn’t thought of the idea before, as an additional protection against hostile spirits at my own apartment. To the beings of the immaterial, ghost dust was incontrovertible solidity. Thrown directly at a ghost, it would cause tremendous pain and paralyze it for a little while, as if the spook had been suddenly loaded down with an incredible and unexpected weight. If I’d put it all over my walls, it would have turned them into a solid obstacle to ghosts and their ilk, shutting them out with obdurate immobility.
Of course, my recipe had used depleted uranium dust, which would have made it just a tad silly to spread around the interior of my apartment.


Ghost Story Chapter 4, Page 34