Visual and Physical Degradation of the Black and White Mosaic of a Roman Domus under Palazzo Valentini in Rome: A Preliminary Study

Abstract

Palazzo Valentini, the institutional head office of Città Metropolitana di Roma Capitale, stands in in a crucial position in the Roman archaeological and urban contexts, exactly between the Fora valley, Quirinal Hill slopes, and Campus Martius. It stands on a second-century A.D. complex to which belong, between other archeological remains, two richly decorated aristocratic domus. One of these buildings, the domus A, presents an outward porticoed room with a fourth-century AD central impluvium (open air part of the atrium designed to carry away rainwater) with a black/white tiled mosaic pavement, the preservation status of which is compromised by an incoherent degradation product that has caused gradual detachment of the mosaic tiles. To identify the product and determine the causes of degradation, samples of the product were taken and subjected to SEM-EDS, XRF, NMR, FT-IR and GC-MS analyses. The findings reported in this study can help restorers, archaeologists and conservation scientists in order to improve knowledge about the Roman mosaic, its construction phases, conservation problems and proper solutions.

Keywords: FT-IR; GC-MS; NMR; Roman domus; mosaic restoration; multi-method diagnostic.

Figure 1

In the red circle is evidenced Palazzo Valentini (source: Google Earth [9]) (a). The paviment mosaic and the immediately facing wall (b).

Figure 2

Photos of the degradation (a) of the floor and (b) of the wall and optical microscope image (c) on the surface of the black and white mosaic pavement (10× and 40× magnification, respectively; width focusing 25 mm, 2 mm increments; 6 V/20 W halogen light). The sample of the degradation product of the black and white pavement mosaic of domus B was analyzed under an optical microscope in transmittance and reflectance).

Figure 2

Photos of the degradation (a) of the floor and (b) of the wall and optical microscope image (c) on the surface of the black and white mosaic pavement (10× and 40× magnification, respectively; width focusing 25 mm, 2 mm increments; 6 V/20 W halogen light). The sample of the degradation product of the black and white pavement mosaic of domus B was analyzed under an optical microscope in transmittance and reflectance).

Figure 3

(a) Photo of the samples of the degradation product of both the floor and the wall (glass Petri plate 80 mm); (b) photo of the degradation product of the pavimental mosaic taken by the optical microscope (1000× magnification; width focusing 25 mm, 2 mm increments; 6 V/20 W halogen light).

Figure 4

SEM micrographs of the samples collected from pavimental mosaic (a,b) and from the wall (c,d).

Figure 5

EDS spectra of (a) floor sample and (b) wall sample. For experimental condition: see Section 4 (Materials and Methods).

Figure 6

SEM photo (a) and EDS spectrum (b) of the spot of the particle “A” of the wall sample. For experimental condition: see Section 4 (Materials and Methods).

Figure 7

¹H-NMR spectra (300 MHz, CDCl₃) of (a) wall and (b) pavement samples.

Figure 8

FT-IR spectra (4000–400 cm⁻¹; Globar source and deuterated triglycine sulfate, DTGS, detector; 200 scans; resolution 2 cm⁻¹) of samples taken from (a) wall and (b) floor (CaCO₃ 875 cm⁻¹; CaSO₄ 607 cm⁻¹). The red/black and green/blue spectra in figure (a) and figure (b), respectively, are related to two different samples from wall (a) and floor (b). The blue boxes show the signals due to calcium sulfate.

Figure 9

GC-MS chromatogram (fused-silica capillary column, HP-5MS; stationary phase SE54; 30 m × 0.25 mm I.D. and 0.25 µm d_f; T_inj 300 °C; splitless mode 30 s; T transfer line 200 °C; program: T₀ 120 °C, isothermal for 1 min, 30 °C min⁻¹ up to 200 °C, 5 °C min⁻¹ up 230 °C, then 30 °C min⁻¹ up to T final 290 °C; carrier gas He; m/z from 50 to 700 at 70 eV.) of a pavement sample. Peaks: 1 hexadecane, 2 octadecane, 3 nonyl 2-propyl ester sulfurous acid, 4 tributylchloro-stannane. Mass spectra are shown in Figure S4 of the Supplementary Material.