Encaustic is a technique notably used in the Fayum mummy portraits in Egypt around 100-300 AD. The word originates from the Greek word enkaustikos which means to burn in, and this element of heat is necessary for a painting to be called encaustic. It is also known as hot wax painting. I use a mixture of heated beeswax and damar resin to which colored pigments are added.

Encaustic on cypress panel: portrait of a woman from Al-Faiyum, Egypt, Roman Period,
circa 100-150 C.E. Milwaukee Art Museum, Wisconsin