I sand the surface with 220 grit then apply two coats of acrylic enamel. While the paint is still wet, pock the surface in random locations with a blunted nail and score here and there with a dull screwdriver. When dry, I coat with a thinned down acrylic matte black then wipe with damp rag to smear into cracks and expose the color. Finish with a good polyurethane.