Encaustic, sometimes known as "hot wax painting" is an ancient technique. A mix of beeswax and damar resin is heated to the liquid stage, then mixed with pigmentation. The resulting medium is applied to a rigid surface (typically wood panels). After applying a layer of wax medium, heat is applied to the work (heat gun or blowtorch), which creates a fusion of wax and wood.
Before the wax cools, an artist can do all sorts of things to the piece. Metal tools or special brushes can shape and/or texture the substance (layers of which can be anywhere from thin to relief-map thick). One may even affix objects into the wax, as Jasper Johns is known for doing. Additionally, an encaustic can be polished to a final sheen, or reworked (through use of heat, again) as much as necessary until a final result is achieved.