The exercise was to glue coloured paper at random on a 50x60cm sheet. Then apply transparent layers of acrylic paint over it, finding back the model, but without losing the background. Below you see the early stages. This one took about 45 minutes to make.
The procedure looks quite effortless, but the second that I made was horrible. I consider myself rather lucky with this one.
First: sticking the coloured paper.
Second: finding the contours with pastel and defining them with grey brown acrylic.
Third: blocking in the shadowed parts and light spots.
Fourth and final (top painting): adding details and painting the in between hues of colour.