In the example above, I demonstrated to a private student how to use the grid method. I can go into this in more detail if enough people are interested, but essentially, your source material (photo, magazine image, quick sketch or cartoon, etc...) gets a grid drawn over it with equal divisions (unless you are trying to distort it, use perfect squares). Then, on your painting surface, larger or smaller, place a matching grid. It must match line for line, also with perfect squares, same number of squares. Whether the subsequent squares are larger or smaller does not matter but will make your drawing proportionately larger or smaller. You will use this to assist you in drawing accurately the contents of each square — example the left-most eye starts at the intersection of 4 across & 3 down on both the source and final.
Next, begin laying in the distinct shadow pattern. Treat it as if you have only a black marker and white paper. Get the pattern in. Just get it in. In this example, I am using a warmish mixture of Alizarin, Ultramarine Blue and Raw Umber for my darks.
You will want to paint in lighter values. Don't. Get the shadow pattern in. In areas that are dark, but may actually be lit by the source light, make them dark anyway. You can always lighten them later. Try to connect all shadow areas to others. No islands.
My apologies for the huge reflections in the wet paint. I had set the camera up over my shoulder using window light, before there was paint on the canvas, then just reached over my shoulder to snap new shots, and did not anticipate the reflection.
Be careful not to over-model the halftones in the light pattern. Keep your lights and darks separate. Mind your cool highlights if working with north light.
by David R. Darrow