I am contemplating doing a triptych of 18" square pieces based upon this sample I did in the Asheville Patricia Baldwin Seggebruch worksop. Last time I used a lot of propane gas burning wood to achieve a dark brown background. My arms got tired and the wood warped with the heat so I'm trying out some alternative (and fine art friendly) stains. We have four possibilities in the running: walnut ink, a soy based stain, ink tinted encaustic gesso, and strongly brewed coffee.
A 1/2 teaspoon of alum was added to the coffee after it cooled to act as a fixative. I read about that here. For you coffee nuts out there, I am not wasting good coffee, merely the $1.49 pre-ground, store brand stuff in the tin. As a total tea nut, I thought I'd better put that out there.