" I thought I had one of your father, but it didn’t develop.” Tremaine nodded ruefully. “It’s the silver nitrate in the film stock. He doesn’t show up on it.” Giaren stared at her blankly. “That was a joke,” she added belatedly. “Oh.” He sounded relieved. "

― Martha Wells , The Gate of Gods (The Fall of Ile-Rien, #3)