" This is a powder that when applied to the air causes ghosts to become visible,” Henry said.

Magnus tilted the jar of shining grains up to the lamp admiringly, and when Henry beamed in an
encouraging fashion, Magnus removed the cork.
“It seems very fine to me,” he said, and on a whim he poured it upon his hand. It coated his brown skin, gloving one hand in shimmering luminescence. “And in addition to its practical uses, it would seem to work for cosmetic purposes. This powder would make my very skin glimmer for eternity.”
Henry frowned. “Not eternity,” he said, but then he brightened. “But I could make you up another batch whenever you please!”
“I could shine at will!” Magnus grinned at Henry "

― Cassandra Clare , Clockwork Princess (The Infernal Devices, #3)