After finishing my second black and white diptych, I went back and worked on the first one I'd started much earlier. While I liked the basic lines of it and didn't want to mess too much with the negative spaces, I felt it needed a bit more interest and spontaneity.
Using a brush saturated with thin mars black acrylic, I added more to the knobby shapes, pressing the brush against the canvas so that the paint would puddle and drip a bit. I also played around with the other shapes, and let the brush drip and feather, creating "controlled accidents."
I think this diptych is now more interesting than in its previous incarnation.