Raman spectroscopy as a tool to diagnose the impact and conservation state of Pompeian second and fourth style wall paintings exposed to diverse environments (House of Marcus Lucretius)

Abstract

The House of Marcus Lucretius preserves the remains of paintings of the so-called Pompeian second, third and fourth styles. In this work, samples from the second style painting (architectural style AD 40-80), buried in the ground and not exposed to open air, recovered from recent excavations (2004)(2005)(2006), were analyzed. Moreover, wall paintings and wall fragments from the fourth style (baroque ornate style, before Vesuvius eruption), excavated about 150 years ago and exposed since then to outdoors, were also analyzed. Raman spectroscopy was used to characterize the original composition and decay products in the mortars and pigment layers. These spectroscopic results were complemented with quantitative analysis (ionic chromatography) of soluble salts and chemometric and chemical equilibrium calculations. Probable decay pathways are proposed to explain the formation of some decay products of red pigments and for the original components of the mortars. Moreover, a final diagnosis as well as comparison of the conservation state of the mortars and pigments exposed to two different kinds of environments (outdoors and under a burial) is discussed emphasizing the importance of SO x impacts on the open air artworks.

On the stability of mediaeval inorganic pigments: a literature review of the effect of climate, material selection, biological activity, analysis and conservation treatments

“…Synergy with photodegradation and oxidation [64,66] Involved in discolouration and sulphation [106,197,199,202,203,[207][208][209] Unstable [103,123,200], but still used in wall paintings [73,193,[201][202][203] Red Red lead…”

“…Moreover, some issues are encountered on wall paintings. In fact, coquimbite/paracoquimbite Fe 2 (SO 4 ) 3 ·9(H 2 O) were identified in Pompeii, together with magnetite Fe 3 O 4 and gypsum CaSO 4 ·2H 2 O, as a result of the degradation of the fresco paint layer due to SO 2 pollution [73]. On wall paintings in the Tournai Cathedral, on the other hand, anhydrous haematite was found to be converted to iron oxy-hydroxides due to the humid conditions, which resulted in a visible discolouration of some red areas [53].…”

Raman spectroscopy in art and archaeology

“…Wall painting fragments from a Pompeian House (Italy), exposed to two different environments, were analysed and compared by Maguregui et al [6] Samples from the second style painting, buried in the ground and not exposed to open air, recovered from recent excavations (2004)(2005)(2006), and samples from the fourth style, excavated about 150 years ago and exposed since then to the open air, gave completely different results on the composition of the decayed products found together with the original ones. Probable decaying pathways were proposed to explain the formation of some decaying products (magnetite mainly) of red pigments and for the original components of the mortars, specially the whole process leading to the formation of coquimbite (nonahydrate iron sulphate).…”

Spectroscopic analysis used to uncover the original paint colour of the Helsinki Government Palace tower clock faces

“…Unfortunately, even though the in situ approach often supplies enough information about the nature and state of preservation of the artwork [14], the obtained data comes only from the surface of the studied object. Therefore, if the composition of individual layer of a multi-layered sample is required, e.g., paint chip, then, destructive sampling techniques is required [15].…”