What was encaustic
The Roman writer Pliny the Elder (1st century AD) states that from the oldest Greek masters –such as Polygnotus– onward, encaustic was a common painting technique in ancient Greece and Rome (Pliny, Natural History 35, 122-150) . This text appears in chapters "on the artists who painted with encaustic by means of palette knife or brush" –as stated in the treatise’s index (Pliny, N.H. 35, 39-41), which is in fact a history of ancient Greek and Roman painting.
Ancient sources provide numerous references to the use of encaustic painting among artists:
"The imaginations of lovers, being [...] painted with encaustic, leave the images of things imprinted in the memory: moving, living, speaking, and remaining for a long time." Plutarch, Amatorius 759 c. (1st-2nd centuries AD).
"There and then a thousand types of bronze and ancient ivory and encaustic painting [wax] with its lying shapes as if about to speak I did learn of. For who has ever discerned with the eyes of Vindex, determined to identify the old masters in the arts and recapturing the sculptors of statues which have no labels? What bronzes kept brilliant Myron up late nights, what marbles came to life at the hand of laboring Praxiteles, what ivories were smoothed by the thumb of Phidias, what was ordered to live and breathe in the furnaces of Polykleitos, what lines across time confess their creator Apelles, this man will show you." Statius, Silvae 4, 6, 20. (1st century AD).
Boethius mentions among the necessities for painting "the boards entrusted to the hands of workers, the waxes collected by the observation of farmers, the pigments obtained by the skill of the traders, the canvases manufactured by diligent weavers". Boethius, De Arithmetica, 0, 4. (5th-6th centuries AD).
"Thanks to God, for a more durable and lifely paint, he has painted our image not on wooden tablets that decay nor with liquid waxes, but he has engraved it in the flesh of your heart." Paulin of Nole. Letters 30. (4th-5th centuries AD).
"The story has stayed in my mind indelibly like an encaustic picture." Plato, Timaeus 26c. (5th-4th centuries BC)
"The city [of Tanagra] lies on a rocky height. [...] The entrance halls of their houses and the encaustic paintings they display give the city a beautiful appearance." Herakleides of Crete, 1, 8-9, 12. cf. Graham Shipley, The Greek world after Alexander, 323-30 B.C. p. 29. (3rd century BC).
"To Hektoridas, for a model of the encaustic painting of the lions' heads, 16 drachmas and 1/2 obol". Building accounts of the temple of Asklepios at Epidauros, IG 421 no. 102 line 303.
The use of encaustic in ornamentation of buildings in Classical Greece can be found in the accounts of construction works of the temples at Eleusis, and in reconstruction works of the temple at Delphos. Cros, Henry, L´Encaustique et les autres Procédés de Peinture chez les Anciens. Paris, 1884, 48.
W. B. Sarsfield (A manual of fresco and encaustic painting, London, 1843, 132) observes that Himerius (Himer., Eclog. 4) (4th century AD), the Pandects of Justinian (Book 17) (6th century AD), and the acts of the second council of Nicaea (8th century AD) (Council, Nic.II., act v, col. 309; act vi, col. 375-376 -ed. 1714-) are "witnesses of the favour with which encaustic painting was regarded, and of the extensive patronage it continued to receive at Constantinople and in its dependencies in their times".
Cros and Henry state that writers of the early times of Christianity "do not seem to know a different painting technique than encaustic". H.Cros, C.Henry, 1884, 76.