Vertical edge - large
What I call the "vertical edge" is the key to the whole technique that I am talking about. It is this black area that gives the impression of depth by forming pseudo-shadows. Whilst I have shown the two flat planes to be the same colour, they could just as well be different. It is vitally important that the paint you use is not thin enough to run down over this edge. Take a good look at people in different lighting and you will see that they have inumerable edge shadows on them. I cannot stress enough the importance of looking at the prototype to see how well this technique mimics the look.
I use artist tube acrylic paints for my figures. The paint as it comes out of the tube is about the right consistency to use. It is brushed across the edges, and across the folds. These steps are shown in "Painting an O scale figure".