Chemical studies of ancient encaustic painting on board and canvas
The Roman-Egyptian funerary portraits of Fayum are the largest body of easel painting of the Roman era to have survived. Most of them were painted in encaustic on wood or canvas during the 1st to 3rd centuries AD. Chemical studies of these paintings suggest that some of them could have been with an encaustic paint composed of beeswax and soap.
Beeswax is composed mainly of hydrocarbons and esters. Soap is composed mainly of carboxylates (salts of fatty acids) plus alcohol (glycerine).
At left, the infrared spectrum of beeswax (1) and soap (2) with the absorption bands that characterize them, identifying the medium of the water-soluble encaustic, composed mainly of these two substances.
Above at right, the infrared spectra of a reference sample composed of beeswax and soap, and that of the medium found in the Fayum Roman-Egyptian portraits painted in encaustic on panel.
IR1. Reference sample of beeswax and soap analyzed by Pedro Cuní1 .
IR2. Portrait of a woman. Antinoopolis, Egypt, 138-161 AD. Musée des Beaux-Arts de Dijon, France2 .
IR3. Portrait of a of a man Egypt. Encaustic on panel. 43,8×19,7 cm. 150-200 AD. Brooklyn Museum, New York. 150-2001 .
IR4. Portrait of a woman. Musée du Louvre, Paris3 .
Infrared studies of the paint medium in these works identified presence of beeswax and soap.
At left, Fayum portrait. El-Rubaiyat, Egypt, 125-150 AD. Encaustic on wood. h: 25 cm. Ny Carlsberg Glyptotek, Copenhagen. At right, Fayum portrait. El-Rubaiyat, Egypt, 140-160 AD. Encaustic on wood. h: 25 cm. Ny Carlsberg Glyptotek, Copenhagen.
FTIR spectra of paint samples from these two portraits showed absorption bands of beeswax and soap6 .
Analyses by gas chromatography of Fayum portraits also indicate presence of beeswax and soap.
At left, Portrait of a man. Encaustic on canvas. Probably from Antinoopolis (Fayum, Egypt). 3rd century AD. Benaki Museum, Athens.
The chromatographic analysis of this work indicates the presence of saponified beeswax and fatty acids4 .
At right, Mummy of Herakleides, Egypt, about AD 150. Encaustic on wood. 175x44x33 cm. The J. Paul Getty Museum, Malibu.
Beeswax and fatty acids possibly saponified were identified by GC/MS7 .
The analysis by gas chromatography-mass spectrometry of a Fayum portrait in the Museum of Fine Arts in Boston, shows patterns of fatty acids and hydrocarbons characteristic of beeswax, with a level of fatty acids significantly higher than that of the sample of reference beeswax5 .
At left, Portrait of a man. Encaustic on wood. El-Rubaiyat, Fayum, Egypt, about AD 170. 44x19cm. Museum of Fine Arts, Boston.