It’s almost too simple: a large pot of strong coffee (I used day-old coffee) + a few prints immediately following their final wash. Time, temperature, and paper-type will yield varying effects on the final print. Make sure you do a final wash/rinse to eliminate any excess coffee!
Below are a few experimental darkroom prints I toned in coffee:
Want a visual basic on the “How To?” Here’s a Youtube video by The Art of Photography outlining his methods for toning darkroom prints with both coffee and tea. Organic methods for adding a little somethin-somethin to your darkroom prints. Check it out!