The first staining test went well; I had not anticipated the amount of dust that got kicked up, but it was easy enough to blow it off the work surface. I used a sanguine conte crayon to lay down the color, then brushed on a PVA-based sealer.

The dry, clean plate:


Just the crayon pigment:


After the seal dried (NB: this is labeled as a matte seal):


The main problem I have with this technique is the poor contrast between the inscribed letters and the flat surface.  I have a few other ideas for laying down the pigment, as well as inlaying some sort of color into the letters, to try out. We shall see.