When painting red rock, use purple in the shadows to avoid a leathery feel. Also, if you spatter one area of rock, you'd better spatter other places in the painting. Make sure your image looks consistent. If the red rock looks too pink, do a wash of yellow over them... but only do that type of thing on the lights. If you do a wash in a dark area, it will look pale and ugly when it dries unless you are using a transparent paint. It's a good idea to pre-mix your over-arching colors (hah!). I mixed a whole bunch of dark brown and reddish orange and put them in little 35 mm film canisters (idea from Rob). To get the cracks working on the rock faces, sculpt each area so that there is light, dark, reflected light, and cast shadow. Rob also suggested I make the foreground bush leaves brighter than they were in my photo. They had been the same value and they kept getting lost in the shadow of the arch behind it. Rob's a genious. Some things I learned: To get rock looking like rock, make sure the strokes are bold and crisp. When they get faded and weak, they don't look like rock. Finally, when you need a highlight after you've already painted an area, put down some white, let it dry, then mix the correct color and value to paint over the white area.
One more tip for all those who don't get to have a Rob Mckay in their painting education... Up until now, I NEVER NEVER NEVER used black in my paintings. A lot of people claim that it kills a painting. When you're restricted to the 5 paint tube colors listed below, there are a couple of REALLY REALLY REALLY useful purposes for the black paint... 1. Quinacradone Magenta mixed with black makes a KILLER burnt sienna. 2. Add a bit of Black to your Cad Yellow, and you get a GREAT realistic-looking green.
11" x 14" acrylic on illustration board. 13 hours. Paint tube colors used to mix everything: Cadmium Yellow, Quinacradone Magenta, Manganese Blue, Mars Black and Titanium White.