Characterization of Waxes in the Roman Wall Paintings of the Herculaneum Site (Italy)

A multi-analytical approach is proposed for the detection and quantitative characterization of waxes in wall paintings from the Vesuvian area, in particular in the House of the Skeleton, the House of the Deer and the House of the two Atriums in Herculaneum (Italy). Different types of waxes, of animal, vegetable, mineral and artificial origin, were investigated, as reference materials, by Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy and gas chromatography coupled with mass spectrometry (GC/MS). The obtained results were compared with those found on samples from the wall paintings of Herculaneum. By non-destructive techniques, Raman and FTIR spectroscopies, waxes were generally found in the wall painting fragments investigated. A more quantitative characterization by GC/MS analysis, performed on three representative samples on the three houses, allowed highlighting the features of beeswax. In addition to beeswax, candelilla wax and an artificial wax, compatible with the formulated candelilla wax, were also detected. The presence of candelilla, a vegetable wax introduced in Europe after the sixteenth century, suggests maintenance works probably carried out with the aim of preserving the original colors of the paintings. In addition, by Raman and FTIR spectroscopies hematite and Egyptian blue pigments were identified. Calcite, aragonite and gypsum were also detected.