I paint with casein paint, but you could make anything into a casein paint. There is an emulsion that you can buy and add your pigments to that. You could add your natural materials and ground up rocks besides your gouache and watercolors.
I'm a lumberjack and I'm okay, I sleep all night and work all day. Tiny lumberjack ad:
World Domination Gardening 3-DVD set. Gardening with an excavator. richsoil.com/wdg