Every spring semester I teach an oil painting class for sophomore illustration majors and I introduce several techniques using an egg as the subject. The egg offers a simple breakdown of value offering a clear and concise mapping of the different lights and shadows.
They poke one hole in the top and bottom of the egg and blow out the contents (gross) and then they have an egg to work with for several weeks. They use different lighting effects as well as oil painting techniques. Underpainting in acrylics and over painting in oils, wipe outs, mounted drawings with overpainted color, glazing and scumbling and much more.
It's a challenge but it's a great build up to the trompe l'oeil project. It's gotten fun for me to do and now I have a serious collection of eggs!