Radiocarbon Dating of Mortar Fragments from the Fresco of a Romanian Monastery: A Field Study

Abstract

The stone Ensemble from Corbii de Piatrǎ Romania arouses a continuous scientific interest, with the final goal being to obtain an exhaustive and multidisciplinary package of results that will become the support of an extensive restoration project. The cave painting stands out as the most important and most affected by the advanced degradation among the historical monuments in Romania. This article provides for the first time a radiocarbon dating of the first forms of painting by establishing the age of the mortar/plaster used as a pictorial support. Being a very complex context from the point of view of the type of datable material and the disappearance over time through degradation of other elements that would ensure a simpler and more reliable radiocarbon dating (such as the straws used to form the material), it was necessary to use a multidisciplinary approach for the selection of samples and for supporting the radiocarbon results. The set of analyses consisted of visualization techniques through microscopy and compositional analysis, providing information on the similarities/differences between the samples, the degradation mechanisms/impurities and the quality of the calcium carbonate dated by the Accelerator Mass Spectrometry (AMS) technique. The results supported each other, ensured the selection of reliable radiocarbon data and established the most probable moment of the early interventions, namely the two phases corresponding to the 14th century.

Keywords: accelerator mass spectrometry; cave painting; compositional analysis; electron microscopy; radiocarbon dating.

Figure 1

Corbii de Piatrǎ rupestral church: (A) exterior view, tiled wall (Photo: Simion, C. A.); (B,C) interior view for ship-type structure (Photo: Valcea, A. E.).

Figure 1

Corbii de Piatrǎ rupestral church: (A) exterior view, tiled wall (Photo: Simion, C. A.); (B,C) interior view for ship-type structure (Photo: Valcea, A. E.).

Figure 2

Map with the researched area, modified after Ghiran et al., 2023 [14]; (a) Occurrence of Southern Carpathian (Google Earth source); (b) Simplified tectonic map of the Getic Depression, modified from Sandulescu, 1984 [15]; (c) The studied area with location of the Corbii de Piatră monastery on Oligocene Corbi Formation, modified after Murgeanu et al., 1967 [16].

Figure 3

Corbii de Piatrǎ church: (A) the second square from the altar on the northern wall from where sample N was taken, divided into fragments N1, N2, N3 for radiocarbon dating (Photo: Simion, C. A); (B) the second square from the altar on the southern wall from where sample S was taken, divided into fragments S1, S2 for radiocarbon dating (Photo: Simion, C. A).

Figure 4

Corbii de Piatrǎ church; details of the leftovers from the samples prepared for radiocarbon dating, used in the preliminary analyses: (A) remains from the sample of the northern wall; (B) remains from the sample of the southern wall.

Figure 5

The microstructure of the mortars at the optical microscopic analysis: (A) the friable mortar with low adhesion; (B) the adhesive mortar with high hardness.

Figure 5

The microstructure of the mortars at the optical microscopic analysis: (A) the friable mortar with low adhesion; (B) the adhesive mortar with high hardness.

Figure 6

Fragments of fresco under cathodoluminescence microscopy: (A) fresco fragment with low adhesion to the sandstone wall; (B) fresco fragment with high adhesion to the wall with two distinct areas: an external unaltered sublayer and an internally altered sublayer with high porosity.

Figure 7

SEM-EDS of the sample with small adhesion in cross-section and elemental mapping: (A) surface layer; (B) an area where the mortar shows advanced degradation inside.

Figure 8

The microstructural analysis in cross-section by scanning electron microscopy of the sample with high adhesion revealed the fresco stratigraphy: (A) pictorial layer ×450 WD-10 mm 25 kVcu30si (BSE); (B) intonaco layer ×450 WD-10 mm 25 kVcu30si (BSE) [6].

Figure 9

Qualitative phase analysis by X-ray diffraction of pictorial layer of the fresco element: (A) with low adhesion to the sandstone wall [7], (B) with high adhesion to the sandstone wall [6].

Figure 10

The histograms obtained for the fragments of mortar/lime plasters from the Corbii de Piatrǎ church, separated from the two samples taken, one each for the southern and northern wall, respectively; at the top of each graph, the unique code of the graphitization in RoAMS is indicated (2534.150 for S1, 2535.150 for S2, 2536.150 for N1, 2537.150 for N2, and 2538.150 for N3), as well as the CRA value with the associated measurement uncertainty, both in years BP (according to OxCal version 4.4.4 and [47,48]).

Figure 11

Inscription on the southern wall of the Corbii de Piatrǎ church (Photo: Simion, C. A.).