In my experiments, I’ve established that cobalt blue and the earth tone, quinacridone nickel mix very well to form an earthy green. Today I wanted to see how purple interacted.
On the left side of the purple field, we see a nice transition to the cobalt blue which, in turn makes a transition to green before yielding to the yellow nickel earth tone. On the right side of the purple blob, there is also a transition. Since yellow is the complement of purple, under ideal conditions, their combination should make a neutral gray. However, neither the purple nor the yellow pigments used in the composition above are pure. Whatever the impurities are (perhaps the yellow is on the green side and the purple is on the red side, for example) in these two complements, the result is a pleasing, variegated brown.
I would like to try combining granular pigments like some of the cobalt pigments, with earth tones on a paper with a rougher surface to enhance the optical effects.