Here's an idea.
Are there any examples of people making photographs out of mold, or other bacteria?
Let me explain...
Imagine a carbon print w/o pigment and w/o alcohol and with the possible addition of a "food source". Printed on a piece of paper and left to sit, would it be possible that mold would form in the image bearing portions?
If one was versed in biology and the science of petri dish type experiments, perhaps a whole host of colors, contrast values, etc., could be obtained. Heck, maybe you could even make tri-color photos with the right combination of micro-organisms.
Something to ponder; any biologist out there with any suggestions?