Jan van Eyck (1390 - 1441) was a Flemish painter who is credited with perfecting the technique of oil painting. Previously, artists had painted with egg tempera, but oil paint was more versatile, easier to use and it allowed the artist to create an illusion of depth that was impossible with the earlier medium. Using his own oil painting techniques, Van Eyck was able to paint realistic flesh tones. The key to his success with skin tones lies in his use of verdaccio, a murky green colour. Van Eyck would create a complete underpainting in verdaccio tones prior to using other colour.
Mix equal amounts of mars black, lead white and chromium oxide green oil paint. Thoroughly mix them on your palette, using a palette knife. This is the basic verdaccio paint mix.
Add a small amount of turpentine to thin your verdaccio paint mixture. Use just enough to slightly thin the paint. This will allow you to apply the paint smoothly.
Place nine equal mounds of lead white paint on your palette. Add a tiny amount of verdaccio mixture to the second mound, slightly more verdaccio mixture to the third mound and slightly more than that to the fourth mound. You should notice a gradual difference in colour intensity.
Repeat this process with the other five mounds of white paint.
Place a mound of the original verdaccio mixture to the right of the ninth mound. You will now have 10 mounds of paint, ranging from light to dark. This is the verdaccio that Jan van Eyck used to create an underpainting for skin tones.