Encaustic painting is an ancient technique created by the Greeks. It uses melted wax, originally bees wax mixed with pigments and then altered using resin, originally crystallized tree resin. It gives a very brilliant and long lasting effect. The wax with the pigment is applied to the canvas, wood or plaster and then heat is passed over the surface to create a uniform film. Resin is applied to alter the consistency is necessary. The wax is built up in layers and heated every time to give a rich optical effect and is time consuming and laborious.
An artist during the middle ages would choose another medium over encaustic painting because of how time consuming and laborious it is to do.