Still trying with coffee....
I made a ball-mill to grind it really fine, but it was still not fine enough and the particles separated out. I have tried straight ground coffee and also coffee after it has been through the expresso machine. In all cases, a piece of unsensitsed tissue melts out fine, but every attempt to print has so far ended up as leather on paper that will not even melt when boiled; I seem to be getting some sort of reaction with the gelatine/coffee/dichromate using my normal tissue recipe (one that works fine for soot). Gum printing coffee on the otherhand works fine, although with brushing on the mix it is tricky to get an even coating.
Cocoa powder behaved in a similar manner to coffee, however instead of smelling sweet, it smells really rank after being sensitised and exposed.
What I have found though is that with oils that are inherent in coffee and soot etc., some of the really old glop recipies work the best! My current recipe contains a fair proportion of soap and without adding isoprop alcohol etc., I can pour bubble-free straight after running the glop through a filter. I have often wondered whether adding oil to modern pigments and using the old soap-based glop recipies may be worthwhile, but I need to wait for the weather to cool a little more so that I can start pouring tissue again. I did try grinding straight charcoal (oil free) and then using soapy glop but it foamed like crazy and was a disaster; probably why everone stopped using the old recipies with modern 'clean' pigments.
Best regards,
Evan