ENCAUSTIC. - It is among the oldest known types of painting with an advanced technique; substantially, that painting can be defined as encaustic which uses wax as its binder and is subjected to a hot process (ceris pingere ac picturam inurere, says Pliny).
Documented in Egypt as early as the 7th century B.C., it then passed to Greece as a technique typical of painting on stone and marble and, subsequently, in the decoration of sculpture and architecture. Certainly used by Polygnotus, it was perfected in the 4th century B.C. and reached a high degree of development with the greatest painters of ancient Greece: Nidas, Aristides, Pamphilus, Pausias, Thespis, etc. The stelae of Pagasae constitute a remarkable series of Hellenistic wax paintings, and the portraits of el-Fajjūm in Egypt, from the 1st to the 4th century A.D., are among the most important surviving documents of encaustic painting.
Research on the technique of encaustic was very much in vogue in the eighteenth century, when an attempt was made to revive its procedure, and there were artists such as Mengs and scholars such as Requeno, Viglioli and Donner, who carried out careful studies for the reconstruction of the various encaustic methods used in antiquity.
From two passages of Pliny (Höst. natur., XXXV, 39, 41), supplemented by the mentions of Lucian, of Varro, of Vitruvius, the three ancient techniques of encaustic can be reconstructed: that of wax, that of the cestrum, that of the penicillus.
In the first, a priming of wax was spread while hot, perhaps mixing into it the fundamental or preparatory color, with the cauterium or metal rod, with which the other colors were then also added. This technique was used for painting on stone, on marble and also on wood. The second was limited to encaustic on ivory: the cestrum was used, which was a small rod (sericulum) pointed at one end, to fix the hot wax on the smooth surface, and flat at the other, like a spatula, for the subsequent retouching while hot. To these two techniques the third was then added, perhaps around 400 B.C. The penicillus, or brush, was used, until then known only for tempera painting and for fresco; with it the hot wax, prepared beforehand and diluted with the color, was spread directly, both on stone and on wood. Pliny says that this technique was also employed in the coloring of ships, since the color thus applied was resistant to the sun, to salt and to the winds.
Although modern opinions on the technique of Pompeian and Roman paintings are no longer in agreement regarding the use of encaustic (recent studies have shown, for example, that the paintings of the house of Livia on the Palatine are frescoes, the wax being entirely from later restorations), it is nevertheless certain that the technique of encaustic continued after the fall of the Empire, in the aforementioned paintings of el-Fajjūm and also in other examples of Byzantine art, until at least the 6th century.