I've played around with simulating the tintype effect by taking a film negative and placing it against a black background. With the emulsion side up, and under the right lighting conditions, you can see a positive image, though it's faint. I'm wondering if some different kind of film developer would make the silver stand out with more of a white color. Then spray-paint the reverse side black.
Also, if paper manufacturers would coat their emulsion on a black paper substrate instead of white, perhaps we'd have an alternative form of direct positive paper.
~Joe