How they were painted

These panels were originally painted in many layers. 
 

The very first layer was a preparatory paint layer of white color that was applied to the panel. Sometimes it would be just painted over with oil paint to create the background. 

The backgrounds were either white or very bright in color. After the preparatory layer was dried the stencil was then drawn on. The stencils were then filled in with basic color and then painted again with contour color. Each layer was left to dry before the next was painted. 

The oil paints used were most likely hand-made using linseed oil as the paint binder and then oil turpentine as paint thinner. Oil turpentine is oil that is made from resin of certain pine trees. Then for tempera poppy seed oil, mastic resin, egg white, and egg varnish were used. Other coloring agents were used as well. For earth pigments, golden orchre, Indian red, sooth black, vine black, vermilion, green earth were used. Today they are painted with multiple resin layers.