The Importance of Value Comparison in Realistic Painting ~ by Katherine McNenly
I teach traditional painting techniques and the one constant that everyone has trouble with and I include myself sometimes, is painting the correct value or tone. Tone is basically how light or dark an object is. Sounds easy, but it is not. Because our eyes like to fool us.
When a light shape is near a darker shape, it will look lighter and if a dark shape is near a light shape it will look darker. This is even more complicated when looking at something that is coloured as opposed to something which is all grey. But it is the place where all my students start to interpret form in a realistic manner. We learn to use a value or tonal scale to accurately represent form on a two-dimensional surface.
I am always amazed at this optical illusion. A and B are the exact same tone. Because one is in the light and one in the shadow and because they are surrounded by their opposites in the tonal range it seems that A is darker than B.
This seems very unromantic and dry, but it is such an important part of the magic of representational painting. Once you understand these visual gymnastics of tone, you can see just how difficult, but fun it can be to represent this world of illusions.