Wall Paintings from the Roman Emona (Ljubljana, Slovenia): Characterization of Mortar Layers and Pigments

Abstract

This study concerns the investigation of mortar layers and pigments of wall paintings from the Roman town of Emona (Ljubljana, Slovenia). Fragments of wall paintings consist of up to three preserved mortar layers. The mineralogical–petrographic compositions of the mortars were determined by means of optical microscopy and FT–IR spectroscopy. The investigated samples were divided into several groups based on similar thicknesses of the mortar layer, the binder colour and the composition of an aggregate. Furthermore, the results of mercury intrusion porosimetry showed that mortar layers consisting of carbonate grains exhibited lower porosity with respect to layers with mainly silicate grains, which is attributed to the angular shapes of carbonate aggregate. This is in accordance with the drilling resistance measurement system test (DRMS), confirming that layers with angular carbonate grains are harder than those with addition of rounded silicate ones, due to the good packing effect. The wall paintings were mainly executed using the fresco technique, while for some details secco was used. The identified pigments were red and yellow ochre, green earth, Egyptian blue, carbon black and lime white; all of them belonged to the so‐called austere pigment, which is quite common in Roman wall paintings.

Mineral Pigments in Archaeology: Their Analysis and the Range of Available Materials

“…Yellow ochre was one of the "austere" pigments of Pliny's palette. Goethite yellow ochres have been found across the Roman Empire in all contexts [41][42][43][68][69][70][71].…”

“…Perez-Rodriguez et al [93] have found green earth (possibly a glauconite and celadonite mixture with chlorite) in wall-paintings at the Seville Alcazar. Gutman et al [42] have found celadonite green earths at Emona in Slovenia. Debastiani et al [94] found green earths, sometimes brightened by mixing with yellow ochre or malachite at various sites in Germania Superior (northern Switzerland, southwest Germany and east France).…”

“…The Roman author Pliny the Elder reports known ochre sources and trade links, indeed much of his work referencing the Greek author Theophrastus, showing there was a continuum in use of these materials during the Iron Age and into the early Medieval period. As such, we see red ochres as standard and widely used pigments in both Etruscan and Roman painting [39][40][41][42][43].…”

“…Davy found cakes of "blue frit" in the ruins of the Baths of Titus which his analyses proved were of the same composition as the blue pigment found in the wall paintings [5]. The pigment is used throughout the gamut of Roman painting [40,42,43,71,91]. In the early medieval period, Riederer has identified late occurrences of Egyptian Blue in 9th Century AD Christian wall paintings [169].…”

Raman spectroscopy of minerals and mineral pigments in archaeometry

“…Schmidt et al analysed a sample from a wall painting in a Buddhist cave along the northern Silk Road, and reported atacamite between the mineral pigments. Gutman et al investigated mortar layers and pigments of wall paintings from the Roman town of Emona (Ljubljana, Slovenia), and found common earth pigments. Crupi et al studied the painted surface of plasters withdrawn from different areas of Villa dei Quintili (Rome, Italy), but because of fluorescence problems, the in situ Raman spectra, apart calcite, confirmed only the presence of cinnabar.…”