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Apr 2, 2010 - to characterize two tombs in the Protestant Cemetery of Rome (Italy). M.F. La Russa · S.A. Ruffolo · M. Malagodi · D. Barca ·. R. Cirrincione · A.
Appl Phys A (2010) 100: 865–872 DOI 10.1007/s00339-010-5662-8

Petrographic, biological, and chemical techniques used to characterize two tombs in the Protestant Cemetery of Rome (Italy) M.F. La Russa · S.A. Ruffolo · M. Malagodi · D. Barca · R. Cirrincione · A. Pezzino · G.M. Crisci · D. Miriello

Received: 30 July 2009 / Accepted: 9 March 2010 / Published online: 2 April 2010 © Springer-Verlag 2010

Abstract In this multidisciplinary contribution, several diagnostic tests were carried out in order to characterize the stone materials, forms of alteration, and protective products applied in the past to two monumental tombs located in the Protestant Cemetery of Rome (Italy). The Protestant Cemetery is a very important historic site, and has been included in the List of 100 Most Endangered Sites in the World since 2005. In this work, two of its tombs were studied: those of Karl (or Charles) Brjullov, a Russian painter who lived in the first half of the nineteenth century, and of Lady Elisa Temple, wife of the artist Sir Grenville Temple. The tombs are both made of white marble and travertine, and the same forms of alteration and degradation, such as blackish biological patinas, black crusts, and chromatic alterations, were found on both monuments. Petrographic analysis of the different lithotypes made it possible to determine textural characteristics, evaluate the state of preservation, and formulate some hypotheses about their provenance by means of oxygen and carbon isotopic ratios, and evaluation of maximum grain size (MGS) and shape preferred orientation (SPO) of calcite grains. Laboratory culture analysis identified autotrophic species and, in some cases, black patinas caused by fungal species were found. Lastly, Fourier transform infrared spectroscopy (FT-IR) revealed that some synthetic protective products had

M.F. La Russa () · S.A. Ruffolo · M. Malagodi · D. Barca · G.M. Crisci · D. Miriello Department of Earth Sciences, University of Calabria, Cubo 12b, Via Pietro Bucci, Arcavacata di Rende, Cosenza, Italy e-mail: [email protected] R. Cirrincione · A. Pezzino Department of Geological Sciences, University of Catania, Corso Italia 55, 95129 Catania, Italy

been used in previous, undocumented restoration processes on some portions of both graves.

1 Introduction In the last few decades, the deterioration of stone buildings has been of particular interest to scientists, due to the need for protection, especially in polluted environments. The deterioration of stone is attributed to many different (physical, chemical, and biological) causes. Many studies have also shown the complexity of relationships between biological and physical agents of degradation [1]. This work is a multidisciplinary diagnostic contribution to characterize the stone materials, forms of alteration, and protective products applied in the past to two monumental tombs located in the Protestant Cemetery of Rome: those of Karl (or Charles) Brjullov and Lady Elisa Temple (Fig. 1a–b). The Protestant Cemetery is a very important historic site and has been included in the List of 100 Most Endangered Sites in the World since 2005. Many famous people, for example, the English poets Keats and Shelley and the Italian statesman Antonio Gramsci, are buried here [2]. Karl Pavlovich Brjullov (1799–1852), called Great Karl by his friends, was the first Russian painter of international standing. He is regarded as a key figure in transition from Russian Neoclassicism to Romanticism. His best-known work, The Last Day of Pompeii (1830–1833), is a vast composition, compared by Pushkin and Gogol to the best works of Rubens and Van Dyck. It created a sensation in Italy and established Brjullov as one of the finest European painters of his day [2]. His grave (Fig. 1a) is constituted by a base made of gray marble, while the main body is made of white marble. On

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Fig. 1 (a) The tomb of Charles Brjullov. (b) The tomb of Lady Elisa Temple

a

b

the front side of the artifact a portrait of the artist is sculptured. Lady Elizabeth (Elisa) Temple (died 1809), the wife of Sir Grenville Temple, ninth Baronet, was famous for her beauty. Her tomb (Fig. 1b), with its large base, was constructed in 1810 by the Swedish sculptor Erik Gustaf Göthe, and was one of the first monuments to be located in the

cemetery [2]. The base is made of travertine, while the main body is composed of white marble. Despite the importance of the cemetery and the various conservation measures carried out on it in the past, the tombs show different forms of degradation: (a) brownish-orange chromatic alterations, probably caused by the application

Petrographic, biological, and chemical techniques used to characterize two tombs

of protective products; (b) black pitting patinas due to biological activity, which cover several portions of tombs; and (c) black crusts. This paper describes the various specimens sampled from the two monuments, which were studied in detail using several analytical techniques. Polarized optical microscopy, scanning electron microscopy with energy-dispersive spectroscopy (SEM/EDS) studies, oxygen isotopic analysis, the laser ablation inductively coupled plasma-mass spectrometry (ICP-MS) method, Fourier transform infrared spectroscopy (FT-IR), and laboratory culture analysis were all performed in order to study (a) the materials employed to construct the two tombs, and their provenance; (b) identification of the protective products used in past restorations, of which only vague details remain; and (c) identification of microorganisms composing biological patinas.

2 Experimental The two tombs are built of the same stone materials: travertine, used exclusively for the skirting, and marble. Macroscopically, travertine shows large irregular pores, parallel to the bedding plane and often containing large calcified plant fragments. Two types of marble were examined on the Brjullov tomb: a foliated marble on the base, and the main body, in marble. The foliated marble varies in color from light gray to gray, and is characterized by strong anisotropy, due to levels of calcite with different grain size. The marble, common to both tombs, is quite homogeneous in color, ranging from white to off-white and gray. In

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some cases, the groundmass is interrupted by slightly faded grayish veins, usually isolated and limited in length. In particular, Lady Temple’s tomb shows evidence of previous restoration procedures, i.e., the presence of filling mortars applied to some points of the monument. Prior to any sampling, a thorough visual inspection of both tombs was undertaken, and decay categories were established: biological patinas, characterized by microbiological growth; black crusts; and orange chromatic alterations on almost all the surfaces. Thirty samples of natural and artificial stone materials were taken, including their degradation products (see Table 1). For complete characterization of stone materials and alteration and degradation products, several analytical techniques were carried out on the samples: (a) optical microscopy of thin sections and stratigraphic thin sections (Zeiss Axiolab), in order to study microscopic characteristics and the superficial layers of samples; (b) FT-IR, to identify protective products (Nicolet 380, with Smart Orbit accessory; spectral resolution 4 cm−1 ); (c) measurements of stable isotopes of carbon and oxygen, for analysis of marble provenance. Isotopes were determined at the Stable Isotope Laboratories of the Queen’s University of Kingston (Canada). Samples were reacted with BrF5 at ∼650◦ C in nickel bombs, following the procedures described by Kyser et al. [3]. Isotopic analyses were then performed on a DeltaplusXP dual inlet isotope ratio mass spectrometer. The stable carbon isotopic compositions of the samples were determined on a Carlo Erba Elemental Analyser coupled with a Finnigan Mat 252 isotope ratio mass spectrometer. Results are expressed with reference to the standard VDPB

Table 1 List of samples taken from the two tombs Brjullov Tomb

Lady Temple Tomb

Sample ID

Description

Sample ID

Description

CM1

Marble

CM16

Marble

CM2

Marble

CM17

Travertine

CM3

Travertine

CM18

Marble with chromatic alteration

CM4

Foliated marble

CM19

Marble with chromatic alteration

CM5

Marble

CM20

Marble with chromatic alteration

CM6

Marble

CM21

Marble with chromatic alteration

CM7

Biological patina

CM22

Marble

CM8

Marble with chromatic alteration

CM23

Marble

CM9

Marble with chromatic alteration

CM24

Biological patina

CM10

Stucco

CM25

Marble

CM11

Stucco

CM26

Marble

CM12

Biological patina

CM27

Marble

CM13

Mortar

CM28

Marble

CM14

Mortar

CM29

Marble

CM15

Mortar

CM30

Black crust

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(Belemnitella americana from the Cretaceous Pee Dee Formation, South Carolina); (d) culture analysis was carried out in the laboratory under sterile environmental control conditions, according to current regulations [4, 5]. In particular, species were grown on both liquid and solid substrates and identified by transmitted optical microscopy [6]; (e) Mn contents were ascertained by the laser ablation ICP-MS method. The equipment was an Elan DRCe (Perkin Elmer/SCIEX) connected to a New Wave UP213 solid-state Nd-YAG laser probe (213 nm). This instrumentation can rapidly analyze solid samples and determine trace element concentrations to ppb levels, without any sample manipulation. In this study, ablation was performed with spots of 80 µm, a constant laser repetition rate of 10 Hz, and a fluence of w20 J/cm2 . Data were transmitted to a PC and processed by the GLITTER program; calibration was performed with glass reference material NIST 612–50 ppm [7], in conjunction with internal standardization, applying CaO concentrations [8] from SEM-EDS analyses. In order to evaluate possible errors within each analytical sequence, determinations were also made on BCR 2G glass reference material as an unknown sample, and element concentrations were compared with reference values from the literature. Fig. 2 Thin sections of (a) travertine; (b) foliated marble

3 Results and discussion 3.1 Polarized optical microscopy Petrographic analysis was carried out in order (a) to determine textural characteristics, formulate hypotheses about the provenance of the stone, evaluate shape preferred orientation (SPO) and maximum grain size (MGS) of calcite grains, an important fingerprinting parameter for determine the provenance of marbles [9]. The MGS was determined by measuring the largest calcite grain found in a thin section; (b) to establish the extent of weathering of superficial layers; (c) to characterize the mortar employed in previous restoration processes. 3.1.1 Petrographic characterization of stone Analysis of thin sections showed that all travertine samples are composed largely of calcite, with typically crustified, fine-grained, porous cement (see Fig. 2a). Rhombohedral crystals of newly formed calcite demonstrate evident twinning, well visible in the pores of deposits. All the marble samples have a polygonal granoblastic lineated fabric, composed of calcite crystals with MGS of about 0.7 mm; grains of nearly isometric shape (no evident grain-shape orientation) and no crystallographic preferred orientation were observed; 120◦ triple junctions were frequent. In particular, absence of an SPO indicates that the rock used in the monuments was not subjected to a high strain

due to deformational events; this phenomenon leads to the development of foliation and SPO in calcite grains. Wedge-shaped or conjugate polysynthetic twins, attributed to a deformation mechanism, were also noted. These marbles have low porosity. Only sample CM4 shows a portion with a vein composed of small calcite crystals (5–20 micrometers), representing a preferential direction for deformational processes (see Fig. 2b). Opaque oxides, muscovite, and quartz are accessory minerals. On the basis of petrographic features (MGS and SPO), all samples show the typical features of Carrara marble (Fig. 3) [9]. 3.1.2 Weathering of superficial layer Microscopic observations proved useful for understanding alteration mechanisms and evaluating the extent of decay. In particular, various types of microcracks forming in the marble due to the presence of biological patinas were identified (Fig. 4a). They usually appear in the form of systems made up of many irregularly shaped, short cracks, preferentially along grain boundaries or through the cleavage of single crystals. Optical examination also showed that sample CM30 is coated by a patina with colors ranging from almost colorless

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to dark brown and black, between 10 and 20 micrometers thick, composed of a single layer (Fig. 4b). 3.1.3 Characterization of mortar

Fig. 3 MGS of average range of samples, shown in diagram of historical white marbles [9]

The mortar samples from Lady Temple’s tomb show the same petrographic features. In particular, they are frequently fractured and composed of micritic binder (30% in volume), with a dissolution zone and high primary and secondary porosity. The aggregate is composed of magmatic, metamorphic, and sedimentary rocks, with different mineral phases (quartz, pyroxene, plagioclase, and calcite), together with rare fragments of shales and bioclasts. The distribution of the aggregate is similar in all samples. The grain size of the fragments varies between 45 and 600 µm, on average 400 µm. The elliptical shape of the clasts suggests a fluvial provenance for the aggregate. These results suggest that the specimens of mortar, sampled from various points of the tomb, were applied during the same restoration process (Fig. 4c). 3.2 Isotopic and geochemical analysis Examination of the rock fabric for grain size and accessory mineral content rarely provides a definite basis for identification, because many marbles are physically heterogeneous even when taken from the same quarry. Thus, in order to identify the provenance of the marble in this case, the stable isotopes of carbon and oxygen were measured. Analysis involved measuring the ratios of 13 C/12 C and 18 O/16 O in samples and expressing the results in terms of deviation from a conventional standard, the Pee Dee belemnite, a carbonate fossil. Marble samples from the two tombs show the typical values observed for Carrara marble (see Table 2 and Fig. 5). As noted in the literature [10], the data δ 13 C and δ 18 O values for different provenances vary widely, so that further geochemical data had to be examined. For example, marble from Turkey (Marmara) has comparable δ 13 C and δ 18 O ratios to that from Carrara, but they differ in Mn content. The manganese content does seem to be helpful in identifying marble sources, and the data obtained show that our samples have manganese contents typical of Carrara marble (Fig. 6) [9]. Table 2 Values of oxygen and carbon isotopic ratios

Fig. 4 Thin sections observed in transmitted light (crossed nicols) of (a), (b) marble with dark patina; (c) detail of aggregate and binder of mortar

Sample

δ 13 C‰ (PDB)

δ 18 O‰ (PDB)

CM4

2.7

−1.1

CM5

2.8

−1.3

CM16

1.8

−1.7

CM22

2.2

−1.6

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Fig. 5 Plot of oxygen and carbon isotopic ratios measured in historic white marble: Carrara (C), Afyon (Aph), Marmara (M), Usak (U), Pentelikon (Pe), Paros (Pa), Naxos (N), Thasos (T) (modified from [9])

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Fig. 7 FT-IR spectra (a) of powder samples and (b) extracted samples

evident biological patina were subjected to organic extraction with acetone. The extracted phases were allowed to dry and then analyzed. Samples CM8, CM9, CM18, CM20, and CM21 showed the vibrational bands of a polyester polymer (Fig. 7b). In particular, the bands at 2922 and 2851 cm−1 were attributed to stretching of CH3 and CH2 groups; the absorbance peak at 1724 cm−1 was assigned to stretching of C=O. The bands at 1070 and 1119 cm−1 represent aromatic bending of C–H, and those at 1602 and 1580 cm−1 correspond to stretching of the C=C bond in a disubstituted aromatic group. Instead, the presence in sample CM11 of an acrylic polymer was highlighted by the typical shape of the spectrum (Fig. 7c), with peaks centered at 2922 and 2851 cm−1 (CH2 and CH3 groups) 1740 cm−1 (C=O) and 1100 cm−1 (C–O–C). Fig. 6 Mn content of samples CM4, CM5, and CM16

3.4 Morphological analysis by SEM

3.3 FT-IR analysis

SEM analysis gave more detailed information about chemical degradation processes. Morphological observations of chemical degradation showed dissolution of calcite (Fig. 8a), covering almost all the marble samples. The dissolution of calcium carbonate can be explained with the carbonic acid from rainwater, and with a differential thermal expansion of the calcite [12, 13]. Dissolution resulted in increasingly rough surfaces and clearly occurred preferentially along grain boundaries and cleavage planes. In particular, this process leads to the loss of single crystals or groups of several grains, easily visible under the microscope. The resulting surface appears less serrated, but comparably higher rates of material loss occur. The blackish-gray color is due to biological colonization of the surface. The marble of the Brjullov tomb shows a highly deteriorated surface, due to biopitting. There is no patina, as erosive processes prevail. SEM observations

The spectroscopic study essentially focused on characterizing mineralogical phases and the protective products applied to the monuments during previous restoration processes. In all samples, the stretching vibrations of calcium carbonate (CaCO3 ) peaks at 1409, 705, and 611 cm−1 were identified since the substrate was just a marble. The FT-IR spectrum of sample CM30 shows the presence of typical vibration bands of calcium sulfate hydrate, commonly called gypsum (CaSO4 × 2H2 O), centered at 1109, 669, and 596 cm−1 , as well as the stretching and deformational vibrations of the O–H bond of water at 3525, 3492, and 3401 cm−1 and 1692 and 1627 cm−1 , respectively. See Fig. 7a. Gypsum originates from the transformation of calcite in the presence of sulfur oxides [11]. As some samples contained organic matter used as a protective coating, in order to identify it, specimens without

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Fig. 8 Marble samples. Details of (a) chemical dissolution of surface; (b) microholes induced by biological degradation; (c) algal patinas associated with fungal colonization

Fig. 9 (a) Petri dish with cell growth. Colonies of (b) Chlorophyceae and (c) Alternaria observed in transmitted light

showed biocorrosion (Fig. 8b) in the crystals, with several roundish microholes and diagenetic processes in the calcite, forming spiky calcite as a corrosion pattern. This process is caused by the microbial secretion of inorganic and organic acids (acidolyisis and complexation); these agents dissolve and etch the mineral matrix with subsequent weakening of the binding system [14]. Depending on petrological, morphological, and physicochemical parameters of the stone, biocorrosion results in local “pitting“ (e.g., distinct blind holes, generally of cylindrical shape) and, on a larger scale, in sanding and flaking of the surface, leaving the stone surface eroded and exposed to freeze-thaw deterioration [15]. The destruction of the calcite fabric of the marble is total or partial, according to microclimatic conditions. Clusters of microorganisms, uniformly distributed in pits, are also visible. SEM photographs confirmed their endolithic behavior, with algal patinas associated with colonization by fungi (Fig. 8c). 3.5 Cultural analysis Samples CM7, CM12, CM24, and CM29 were inoculated in a liquid broth culture medium, and then used as tampon

smears on Petri dishes containing nutrients [16], to highlight spore growth vitality (Fig. 9a). Starting from the solid medium, samples were taken from grown colonies and transferred to glass slides for analysis by transmitted light optical microscopy, with magnification up to 40×. Regarding the biological patina on the marble of the Brjullov tomb, the morphology of chloroplasts and cell walls is clear, and they were identified as unicellular green algae (class Chlorophyceae) (Fig. 9b), with slightly oblong cells of various size (5–20 µm diameter). The cells, connected to gelatinous sheaths by fine filaments, form films on moist surfaces. Mucilage is thin and inconspicuous. Each cell has a single, cup-shaped, parietal chloroplast with a single pyrenoid. Samples from the Temple tomb revealed colonies which, cultivated in the laboratory, were fast-growing, olive-black in color, and suede-like to floccose in texture. Under the microscope, branched acropetal chains of multicelled conidia are produced sympodially from elongated conidiophores. The conidia are obclavate, with short conical beaks, pale brown and smooth-walled. Ascomycete fungi of the genus Alternaria were identified (Fig. 9c). Alternaria is a common saprotroph and endophytic on many plants. It is usually isolated from stems and young and old leaves. It is particularly

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frequent on old leaves, and sporulates profusely, especially as the leaf senesces. The diffuse colonization could be related to the microclimatic conditions and also to the presence of polyester polymer on the stone surface. In the literature there has been shown to be an increase of fungal growth on stones treated with polyester-based coating [14]. This phenomenon might be explained by the presence of nonpolymerized or partially polymerized monomers serving as nutrient substrates for microflora [17]. The microbial attack depends on the molecular structure of the polymer used for restoration and the type of chemical links; polyester-based polymers are more susceptible to biodeterioration than polyether-based polyurethanes or acrylic resins [18, 19].

4 Conclusions The state of conservation of the stone material of the two tombs, despite the different restoration processes involving the use of various protective products, testifies to the importance of this research. Analyses provided information about the stone materials and their alteration forms. In particular, petrographic, isotopic, and geochemical analyses confirmed that, in both cases, Carrara marble was used to sculpt the monuments, and was then affected by fractures and microfractures induced by biological patinas. In addition, an evidence of sulfatation process was found only on the Temple tomb. Two organic synthetic polymers (polyester and acrylic) were found on the stone surface of the Brjullov tomb, and it could be hypothesized that at least two different restorations took place in the past on this monument. In the case of the Temple tomb, only a polyester resin was found. This resin might have caused an increase in biological degradation. The Brjullov tomb was extensively colonized by diffuse patinas of green algae of the class Chlorophyceae, probably due to high humidity levels. No heterotrophic microorganisms were found. The same autotrophic colonization of algal patinas on the Temple tomb was also confirmed, and an Alternaria fungus was found on the stone surface. This heterotrophic colonization may be due to the particular location of the tomb (directly under dense foliage and also exposed to traffic fumes) and to organic matter remaining from a previous restoration.

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