Fresco-making is far more difficult than you might expect. The second photo shows the cartoon that needs to be made first to guide the overall painting. All facial/skin features begin with a wash of green (on 'olive' side) as the base. Material has to be worked while still wet, so large areas took days or longer.
The class experience gave me a much greater appreciation in which to view the frescoes I had the opportunity to see while on a recent Italy trip!