The word encaustic originates from the Greek encaustikos meaning, to heat or burn in.

Encaustic is an ancient painting medium that mixes molten beeswax with resin and dry pigments.

There are several steps to painting in encaustic. This differs from other mediums where once you brush on the paint it is usually there to stay.
Once heated to a melting point it is applied to a rigid, absorbent, support. The first step is to apply the molten paint to the surface. This can be done with natural hair brushes, palette knives, or by pouring the paint from cups.

After the paint is on the surface it is re-heated (fused). This is to ensure that the different layers of wax are bonded together and will not flake apart later.

the effect of temperature on encaustic paintings
Encaustics should be cared for as you would for any fine art piece. An encaustic paint film is stable in a temperature range of approximately 40-110°F (4-44°C) In very cold temperatures wax will shrink slightly.
Very hot days can soften the paint somewhat, but will cause no real damage. If any dulling occurs, the surface can be buffed when the painting is cooler. It is best to hang in indirect sunlight.

Encaustics can be wiped clean with a soft cloth or paper towel. If the piece is especially dirty, it can be wiped with a water-dampened cloth.

history
Encaustic painting was practiced by Greek artists as far back as the 5th century B.C.

Wax is an excellent preservative of materials. It was partly from this use that the art of encaustic painting developed. The Greeks applied coatings of wax and resin to weatherproof their ships. Pigmenting the wax gave rise to the decorating of warships. Mention is even made by Homer of the painted ships of the Greek warriors who fought at Troy.

The nature of encaustic to both preserve and color led to its wide use on the stone work of both architecture and statuary. The white marble we see today in the monuments of Greek antiquity was once colored, probably delicately tinted like the figures on the Alexander sarcophagus in the Archeological Museum of Istanbul. Decorative terra cotta work on interiors was also painted with encaustic, a practice that was a forerunner to mosaic trim.

Perhaps the best known of all encaustic work are the Fayum funeral portraits painted in the 1st through 3rd centuries A.D. by Greek painters in Egypt. A significant Greek population had settled in Egypt following its conquest by Alexander, eventually adopting the customs of the Egyptians. This included mummifying their dead. A portrait of the deceased, painted either in the prime of life or after death, was placed over the person's mummy as a memorial. These are the only surviving encaustic works from ancient times. It is notable how fresh the color has remained due to the protection of the wax.