The Servilia tomb: an architecturally and pictorially important Roman building

One hundred and eleven samples from the important Servilia Roman tomb have been analysed for the first time by Raman spectroscopy, resulting in a complete characterisation of the pigment palette used for its remarkable wall paintings: 73 different pigment mixtures have been identified for the composition of its 11 colours and their tonalities. Dyer's weld, an ancient organic yellow pigment, which was described by Vitruvius, has been identified and characterised for the first time in Roman wall paintings. Distinctive Raman spectroscopic signals which differentiate between haematite and caput mortuum (a violet colour from haematite which has been subjected to thermal treatment) are also reported. The use of the very expensive lazurite for a balance relates the importance of this otherwise ordinary instrument with psychostasia (the human soul weighing process) and is not found elsewhere in the tomb. The distribution of white minerals alone or in admixture is not related to any particular colouring pigment or figure; this possibly indicates that there was no specific use for each white mineral and that several craftsmen worked on the paintings, perhaps in different periods, or that the frescoes have been subjected to unrecorded restoration. We conclude that Raman spectroscopy is a valuable analytical technique for the unambiguous identification of mixtures of both organic and inorganic compounds, to study the degree of mineral crystallinity and for identifying treatment. These data are relevant for the holistic interpretation of the artwork in its historical, economical and social context.