I am doing research for a new project, thus rediscovering encaustic (painting with wax and pigment). The term comes from the Greek word for “to heat or burn in” (enkaustikos). Heat is used throughout the process, from melting the beeswax and varnish to fusing the layers of wax. The best known historical examples of such a technique are the more than 600 mummy portraits found in Fayoum, Egypt - 2nd-century A.D. Coptic panel paintings included in mummy wraps. They are striking for their freshness of expression and color, due to the technique in question that is very resistant.
Encaustic is gaining in popularity among contemporary artists as well since it allows for multiple uses and interacts nicely with different materials. It is used with collage, watercolors, shellac, paper (making it transparent), small assemblages, metal foil or powder etc.
The works and YouTube tutorials of Nancy Crawford are among my favorites, but there are many wonders to be found online.