Encaustic from the ancient Greek enkaustikos, means “to heat” or “to burn”. Heat is used at every stage of encaustic painting. The medium consists of beeswax melted with a small amount of resin to impart hardness; it becomes paint when pigment is added to the molten wax. Painting requires the artist to work quickly, for the wax begins to harden the moment it leaves its heat source. What makes encaustic unique—indeed, what makes encaustic encaustic—is the application of heat between layers of brushstrokes. Heat binds each layer to the one set down before it, so while the image may consist of discrete compositional elements, structurally the entire surface is one carefully crafted mass, a whole ball of wax, if you will.
from: Joanne Mattera, The Art of Encaustic Painting