Diego Rivera is likely the most famous Mexican painter/muralist of the twentieth century. He is most well known for his subject matter and his socialist/communistic ties. However, he was also very interested in perfecting his techniques and experimented with the media that he used in painting.
Rivera experimented with a technique called encaustic. This technique uses wax (normally beeswax), resin, thinner and pigment. It is heated for bonding.
The resins that Rivera originally used were lemon resin or elemi, a European material that was expensive to obtain in Mexico. It is thought that he changed to copal, which was readily available in Mexico and was less expensive.
The thinners that Rivera experimented with were lavender essence and turpentine. Oil of spike lavender can leave a residue, which can oxidize and discolor.
Blow torches are used to keep the paint more fluid and to help it fuse with the wax.
History of Encaustic
Encaustic was first used by the Greeks in the fifth century B.C. The word comes from the Greek word "enkaustikos" which means to heat or to burn. They used it for portraits and panels, as well as on ships, as the wax is waterproof. Greek painters brought their skills to Egypt and used this technique to paint portraits over a person's mummy (called Fayum funeral portraits).