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Article

The 20th Century Wall Paintings in the Chapel of the Fallen in Parma Cathedral (Italy): Scientific Investigations for a Correct Conservation Project

by
Laura Bergamonti
1,*,
Claudia Graiff
1,
Silvia Simeti
2 and
Antonella Casoli
1,*
1
Department of Chemistry, Life Sciences and Environmental Sustainability, University of Parma, Parco Area delle Scienze 17/A, 43124 Parma, Italy
2
Archè Restauri s.n.c., Via Chiavari 18/A, 43125 Parma, Italy
*
Authors to whom correspondence should be addressed.
Appl. Sci. 2023, 13(12), 7235; https://doi.org/10.3390/app13127235
Submission received: 31 May 2023 / Revised: 12 June 2023 / Accepted: 15 June 2023 / Published: 17 June 2023
(This article belongs to the Section Materials Science and Engineering)
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Abstract

:

Featured Application

The study presented here provides a better understanding of the materials used in 20th century Italian wall paintings and is useful for the conservation and restoration projects of wall paintings from the same period.

Abstract

In this work, we present a diagnostic study carried out on 20th century wall paintings in the Chapel of the Fallen of the Great War in the Cathedral of Parma (Italy). The Chapel was painted in the two-year period of 1921–1922 and has been recently restored. The paintings were investigated in order to study the technique used by the painter, Biagio Biagetti (Porto Recanati, 1877–Macerata, 1948) and their state of conservation. A total of twelve micro-fragments of the painting layers were sampled and investigated using different techniques. Raman spectroscopy revealed the large amount of different pigments used for each hue, many of them being synthetic materials. SEM/EDS analysis showed that the mortar was an aerial lime obtained from calcium carbonate mixed with a small amount of clay. Organic materials were identified by FTIR spectroscopy. GC/MS investigations revealed lipid and proteinaceous materials in the examined specimens; the lipid fraction, however, is not attributable to the presence of drying oils. From the determination of the amino acid content, it became apparent that the proteinaceous fraction is due to the combination of egg and animal glue; this allowed us to infer the use of “a secco” techniques, confirming the visual impressions of the restorer. The results obtained have contributed to the definition of the conservation project in its various phases.

1. Introduction

The wall paintings of the third chapel of the right aisle of the Cathedral of Parma, Italy are the object of the present study. This chapel, built in the fifteenth-century, was the chapel of patronage of the ancient noble family of the Counts Baiardi, formerly Lalatta, and it is dedicated to the Fallen of the Great War. The construction of a great monument, in perpetual memory of the immense tragedy and the sacrifice of the lives of thousands of young people from Parma, is due to Bishop Guido Maria Conforti, who, in 1918, entrusted the task to the painter, Biagio Biagetti (Porto Recanati, 1877–Macerata, 1948). This was such a civilly and politically significant task that it —in the consisted ofcontext of the nation’s post-war period—the arduous challenge of inserting a modern work into a Romanesque cathedral full of important and ancient sculpted and painted artworks (from the Romanesque sculptural apparatus and the Deposition from the Cross by Benedetto Antelami, also located in the west wall of the chapel itself, to the Dome of Correggio, just to name a few examples).
The chapel was painted in the years between 1921 and 1922, and the various sketches of the artist (1918, 1919, up to the definitive approval of the project in March 1920) reveal a complex and meditated gestation [1,2].
Biagetti was a multifaceted figure. A deeply Catholic painter of purist training, he was a pupil and disciple of Ludovico Seitz, a member of the German school of Nazarenes. He was influenced by the Italian Symbolism and Divisionism movements of the late 1800s (Segantini, Previati, Puvis de Chavannes), giving new impetus to religious art, until a retreat to his initial positions. A prominent figure in the Vatican, he became the first director of the Pontifical Galleries and Apostolic Palaces in 1923, the founder of the Restoration Laboratory of the Vatican Museums, and successively, the director of the Vatican Mosaic Studio.
The Chapel has a neo-medieval architectural style characterized by a Gothic cross vault. Biagetti created the wall decoration with a purely divisionist pictorial technique: fluid brushstrokes, more or less ‘charged’ and tending towards the construction of an immaterial figure, based on the luminist and optical effects of the combination of colors, where the surface of the plaster also contributes to the result, which is a pictorial draft of considerable effect and great visual impact [3].
The characteristic cardboard engravings and the dusting technique of transferring the preparatory drawing onto the fresh plaster, the precise pencil drawing and the joints of the “giornate”, clearly visible on the painted surfaces, have always led to Biagetti’s work being defined as “a fresco”. The deterioration of the pictorial film first appeared in June 1923, shortly after the inauguration, and the painter had to proceed with a series of ‘a secco’ retouches to remedy the presence of extensive stains, still present and attributed to a defective drying of the support mortar. The recent conservative intervention allowed the restorer to carry out a careful analysis of the paintings and of their degradation. In particular, the restorer, observing a pervasive and dramatic loss of adhesion of the pictorial film to the supporting plaster, in turn detached from the underlying masonry, has deemed it necessary to verify the presence of organic binders. Figure 1 shows an image of the east wall, before restoration, where the exfoliation of paint film can be observed.
Before starting the restoration work, a diagnostic study of the materials was necessary in order to learn about the pictorial technique, studying the inorganic and organic materials employed by Biagio Biagetti and, at the same time, to obtain information on the state of conservation of the artifact. A comprehensive understanding of a work of art is a prerequisite for choosing the most suitable conservation method.
Multi-analytical techniques have been used in order to characterize the materials, monitor the conservation of wall paintings, and to identify the paint technique adopted by artists [4]. The most commonly used techniques are scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM-EDS) [5], X-ray fluorescence (XRF) [6], X-ray powder diffraction (XRPD) [7], infrared spectroscopy (FT-IR) [8,9], Raman spectroscopy [10,11,12], high-performance liquid chromatography (HPLC) [13], gas chromatography coupled with mass spectrometry (GC/MS) [14,15], pyrolysis coupled with gas chromatography and mass spectrometry (Py-GC-MS) [16].
In the last decade, the literature on the scientific analysis of wall paintings, a non-renewable form cultural heritage, has increased, with particular interest being paid to the study of the origin and mechanisms of deterioration of the pigments and their distribution and chemical composition [17,18,19,20,21]. The pigments used in the 20th century have been investigated in easel paintings [22,23,24,25], while their use in wall paintings is less studied [26,27].
The art movements of the early 20th century throughout Europe were mainly based on the “a fresco” technique, focusing on the revival of mural painting, leading to the rediscovery of the traditional wall painting techniques [27,28]. Many artists, however, also because of the introduction of new synthetic pigments, experimented with different methods such as the “a secco” or the mixed dry/fresh techniques [27,29]. In the “a fresco” method, pigments are applied to the freshly prepared plaster and are bound through the lime carbonation process without using organic binders. Frequently, the final touches of the works are carried out “a secco”, using an additional organic material such as oil, animal glue, casein, or egg. On wall paintings, organic materials are more difficult to identify and are more susceptible to deterioration than inorganic ones [29].
An interesting work by Izzo et al. [27] reports on the wall paintings of 1930 in Venice (Aula Magna of the Ca’ Foscari University) by Sironi (1885–1961), a famous painter of the first half of the 20th century, and it is focused on his pictorial technique. Most of the painting, in particular, the large monochromatic background, were executed according to the traditional “a fresco” technique. However, the morphology of the principal figures’ stratigraphy suggests the “a secco” technique, with egg yolk and traces of casein and arabic gum as binder for pigments based on zinc, titanium, chromium, and iron.
In a recent study of Iarzulo et al. [30] on wall paintings of the same period as that of Biagetti, made between 1924 and 1926 by famous Italian artist, Gino Severini in the Saint Nicolas de Myre Church at Semsales (Switzerland), the painting technique of the artist was studied. The results reveal that the painter experimented with, in addition to the traditional “a fresco” technique, the “a secco” technique on existing plasters, in particular in association with modern pigments (for example zinc white, cobalt blue, synthetic alizarin and ultramarine blue, cadmium-based yellow, and chromium-based green synthetic pigments).
In this work, a total of 12 micro-fragments of the painting layers were collected and analyzed by means of micro-Raman spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy coupled with energy-dispersive spectroscopy, and gas chromatography coupled with mass spectrometry, to identify pigments, mortars, and binding media.
We believe that this study will enable the attainment of deeper knowledge, which is a significant requirement for the conservation and restoration of these modern wall paintings.

2. Experimental

2.1. Samples

Twelve micro-samples of the painting layers were picked in correspondence with surface cracking. Sampling was carried out following the minimum invasiveness principle. The specimens were obtained by softly rubbing the colored layer to investigate on the organic binding media and pigment palette, the painting technique and preservation state (Figure 2, Table 1). Two micro-fragments were collected to obtain cross-sections in accordance with the methodology reported in [31].

2.2. Instruments and Methods

2.2.1. Optical Microscopy

The Optika SZR-2 (OPTIKA S.r.l., Ponteranica (BG)—Italy) optical stereomicroscope (zoom lenses up to 3.5×, eyepieces up to 20×, maximum magnification of 70×) equipped with a fiber optic system was used to observe the samples. Observations at higher magnifications were made using the Olympus BX40 microscope (Olympus Corporation, Tokio, Japan) integrated into the micro-Raman apparatus, using objectives up to 100×.

2.2.2. Scanning Electron Microscopy Coupled with Energy-Dispersive X-ray Spectroscopy (SEM/EDS)

The morphological analysis of the samples and their elemental composition were performed by means of a Jeol 6400 JSM scanning electron microscope (Jeol Ltd., Tokio, Japan) coupled with an Oxford Instruments (Abingdon-on-Thames, UK) Analytical Link Si(Li) energy-dispersive X-ray detector (15 kV, 0.28 nA, ~1 mm beam diameter, 60 s counting time). INCA-Energy software 6.0 (Oxford Instruments, Abingdon-on-Thames, UK) was used for data processing.
The cross-sections were prepared from samples of the wall paintings. Samples were embedded in epoxy resin and polished to expose the paint layer. The cross sections were applied via a silver conductive paste to an aluminum stub and sputtered with a layer of metallic gold of approx. 8 nm by means of the EMITECH K550 (Labtech International Ltd., Heathfield, UK) sputter coater.

2.2.3. Micro-Raman Spectroscopy

The Jobin Yvon LabRam micro-spectrometer (Jobin Yvon Horiba, Kyoto, Japan) equipped with an integrated Olympus BX40 microscope (Olympus Corporation, Tokio, Japan) with excitations at 473.1 nm from a solid state Nd:YAG laser (50 mW) and at 632.8 nm (He-Ne, 15 mW), was used, in a nearly backscattered geometry, to record the non-polarized Raman spectra. The spectral resolution was about 2–5 cm−1 and 1.5–3 cm−1 at 473.1 nm and at 632.8 nm, respectively. Spectra were acquired by means of an ultra-long working distance 50× microscope objective. The exposures were 10–60 s for 3–5 times. The 520.6 cm−1 Raman band of silicon was used to calibrate the system. Raman spectra were collected on the surface of the samples [17]. The data analysis was done using LabSpec built-in software 350 (Jobin Yvon Horiba, Kyoto, Japan).

2.2.4. Fourier Transform Infrared Spectroscopy (FTIR)

FTIR spectra were recorded in attenuated total reflectance (ATR) mode, using a PerkinElmer Spectrum Two™ FTIR spectrometer (Waltham, MA, USA) equipped with Universal ATR accessory (single-reflection diamond), in the 4000–400 cm−1 range, with a resolution of 4 cm−1 and 16 scans for each spectrum. Data processing was performed using OMNI C 7.1 software.

2.2.5. Gas Chromatography—Mass Spectrometry (GC/MS)

A Hewlett Packard HP 6890 series (Hewlett Packard, Avondale, PA, USA) coupled with a MSD-HP 5973 mass spectrometer (Agilent Technologies, Santa Clara, CA, USA) with single quadrupole and split-splitless injector, was used. Samples were injected in splitless mode at 280 °C. The separation of the components was done by means of a SLB®-5ms Capillary GC Column (L × I.D. 30 m × 0.25 mm, df 0.25 μm) from Sigma Aldrich Supelco (Merck KGaA, Darmstadt, Germany). The carrier gas (He, purity 99.995%) was used in constant flow mode at 20 mL/min. The mass spectrometer was operated in the EI positive mode (70 eV). The wall painting samples (about 1 mg) were hydrolyzed and derivatized following the method for GC/MS analysis of fatty acids and aminoacids present in organic binders reported in [32,33]. The statistical calculation analysis was performed by PAST (PAleontological STatistics) Software 4 (Free software).

2.3. The Conservation Project

The restoration of the wall paintings was very complex due to the pervasive and dramatic loss of adhesion of the pictorial film to the support plaster, which itself had detached from the underlying masonry.
The ‘minimum intervention’ principle was adopted for the conservation plan of the wall paintings. First, the removal of incoherent atmospheric particulate deposits was carried out with very-soft-bristle retouching brushes and simultaneous low-pressure micro-suction of the dust. Then, restoration of the color cohesion (“dusting” color) was performed with Paraloid B 72 at 2% in acetone while restoration of the adhesion defects of the pictorial film to the “intonachino” (ripples, lifting, exfoliations) was made with Primal B 60 (Rohm & Haas, Philadephia, PA, USA) to 2% in demineralised water. The applications were made via infiltration with a syringe and/or by the interposition of Japanese paper.
Finally, the surfaces affected by graying were mainly cleaned using a ‘dry’ method with special rubber latex sponges at neutral pH. Only on the extensive much darker repaintings, presumably by Biagetti himself, a 2% aqueous solution of ammonium citrate tribasic was applied.

3. Results and Discussion

All samples were investigated by micro-Raman spectroscopy and among these, ten were chosen for the identification of the pigments and two (BB7 and BB8) to investigate the type of mortar. Subsequently, chemical analyses for the description of the organic binders were carried out on the representative samples, BB3, BB4, BB5, and BB6, using FTIR spectroscopy and GC/MS. The BB7 and BB8 samples were taken to understand the type of mortar, using the scanning electron microscope with the energy dispersion microprobe (SEM/EDS), after having made stratigraphic sections.

3.1. Identification of Pigments by Means of Raman Spectroscopy

The analysis was carried out on 10 micro-fragments of pictorial film. They have been chosen in order to include all the possible colors present in a significant amount. From the microscope observation it was immediately clear that not all the pigments present in the paintings were represented. The samples are composed by many small brush strokes of different colors. Together with some classical pigments, such as ultramarine blue (Na7Ca(Al6Si6O24)) found in the BB1 and BB6 samples and haematite (Fe2O3), the chromophore phase of red ochre in the BB1, BB2, BB5, and BB10 samples, many synthetic pigments or organic dyes were found in almost all samples (Table 2 and Table 3). Few of them are inorganic compounds, such as cobalt-(II)-stannate (CoO.nSnO2), known as cerulean blue (in BB11), and copper (II) arsenates (Cu2(AsO4)(OH)n) (BB1 and BB3). The Raman spectra of organic pigments, especially in yellow, orange, and red colors, show characteristic features of the class of monoazo- and disazo-pigments but the comparison with the Raman spectra databases and the literature did not allow the complete and unambiguous identification of the dyes [34,35,36,37,38,39,40,41,42,43,44,45,46,47,48]. In only a few cases, the similarities of the spectra with those of contemporary pigments allowed some deductions to be made on their composition. It is very probable that many synthetic pigments used experimentally in the first post-war period were then abandoned or modified in the formulation, and therefore, no longer fully correspond to the current ones. In Figure 2, the Raman spectra of some compounds found on the painting samples, BB1 (blue), BB2 (orange), BB11 (blue), BB12 (yellow) are reported.

3.2. Analysis of Mortars by Means of SEM/EDS

The samples, BB7 and BB8, from mortars were studied via microscopic examination of the cross sections (see Figure 3a,d). The elemental composition of samples was examined by SEM/EDS. It has been observed that the particle size of the inert has a diameter of about 125 µm to 1 mm, as is evident in Figure 3a,c. It can be defined as medium-coarse, sub rounded. The inert–binder ratio, also called thickening, is believed to be around 40–50%. The adhesion of the grain/binder does not seem very good, since cracks can be observed around the grains. About the composition of the inert, from the analyses by EDS (Figure 3b,d), carbonates and quartz can be observed. As for the chemical composition, the mortar would be compatible with a weakly hydraulic lime, but given that it crumbles easily, it is very likely that it is an aerial lime obtained from a calcium-carbonate-containing clay. With regard to the paint layer, thicknesses of about 10 µm were observed for the BB7 sample, (Figure 3b), the same thickness as the BB8 sample, with some grains containing barium (Figure 3d). The results are reported in Table 3.

3.3. Characterization of the Organic Binders by Means of Micro-FT-IR Spectroscopy and GC/MS

3.3.1. Micro-FT-IR Spectroscopy Measurements

The wall painting samples, BB3 (dark green), BB4 (gray), BB5 (red), and BB6 (gray-violet) were preliminarily analyzed by FTIR spectroscopy, in order to verify the presence of organic binders.
By means of FTIR measurements, features of both inorganic and organic materials were detected. In all samples analyzed, calcium sulphate (CaSO4) and calcium carbonate (CaCO3) were present, recognizable by the characteristic vibration bands at 3537, 3407, 1683, 1620, 1106, 671, and 598 cm−1 [32,47], for gypsum and at 1428, 875, and 712 cm−1 for calcium carbonate [48,49]. In the samples, BB4 and BB6, barium sulphate was found, as reported by Raman measurements as well. In BB5, in addition to the characteristic features of haematite (Fe2O3) at 568 and 478 cm−1, the vibrational absorption of quartz (SiO2), usually occuring in red ochre mixed with haematite, at 797, 781, and 693 cm−1 [49,50], was also detected. In the FTIR spectrum of BB6, the bands at about 1015 and 930 cm−1, associated with the blue ultramarine blue pigment (Na7Ca(Al6Si6O24)), were found [51], in agreement with Raman results.
The features ascribed to proteinaceous materials (probably a mixture of egg and animal glue) are clearly visible in all samples: the symmetric and antisymmetric stretching vibrations of CH2 and CH3 in the 2952–2848 cm−1 range; the carbonyl stretching vibration at 1731 cm−1, identificative of egg; amide I at 1643 cm−1 (egg) and 1619 cm−1 (animal glue); and amide II at 1540 cm−1, due to the proteic fraction. In addition to proteinaceous material, polysaccharides were also found: at 3320 cm−1, the stretching vibration of OH groups and at 1020 cm−1, the stretching vibration of the C-O-C glycosidic bond. The use of polysaccharides as binder, in particular, arabic gum, is frequently reported in “illuminated” manuscripts but rarely reported in wall paintings [52,53]. In the BB3 sample, beeswax was identified by the typical doublets at 2916 and 2848 cm−1, at 1472 and 1462 cm−1, and at 730 and 718 cm−1, due to methylene groups stretching and in plane and out of plane bending vibrations, respectively [32,54].
As a representative FTIR spectrum, the measurement recorded on sample BB6 is reported in Figure 4.
However, though the presence of proteinaceous substances is quite clear, FTIR spectroscopy cannot be considered definitive for an accurate identification of organic binders, expecially in the case of mixtures, and does not give reliable quantitative information. Therefore, to verify the presence of amino acids and fatty acids in the binder, GC–MS analyses were performed.

3.3.2. GC/MS Analyses

The investigations by means of GC/MS identified lipid and proteinaceous materials in the samples investigated (BB3, BB4, BB5 and BB6). The lipid fraction detected is not attributable to a drying oil, suggesting that the oil technique was not used in this painting. We found azelaic (nonanedioic acid, saturated dicarboxylic acid), miristic (C14:0), palmitic (C16:0), oleic (C18:1), and stearic (C18:0) acids, but the azelaic acid/palmitic acid ratio being lower than one excludes the presence of siccative oils [55,56].
Figure 5 shows the chromatographic profile of the BB3 sample.
To identify the binding media, the amino acid percentage content in each sample was determined by comparison with the Opificio delle Pietre Dure reference collection in Florence, Italy [57]: a dataset of 43 reference samples of egg (whole, egg white, egg yolk), casein, animal glue, and their mixtures (painted models simulating ancient polychromies). Principal component analysis (PCA) was carried out on the correlation matrix of the relative percentage content of eight amino acids (aspartic acid, glutamic acid, proline, hydroxyproline, phenylalanine, alanine, glycine, and leucine) [17,58,59].
The PCA score plot of the relative percentage content of the eight amino acids in the 43 reference samples and in the artistic samples, BB3, BB4, BB5, and BB6, is reported in Figure 6.
It should be noted that the first main component segregates the reference samples into two large groups: the first (points on the right side of the Cartesian graph) includes those associated with egg (E), milk (M), and egg–milk (EM) and is characterized by the amino acid composition of leucine, aspartic acid, glutamic acid, and phenylalanine; the second group (points on the left of the graph), associated with glue (G), glue–egg (GE), and glue–milk (GM), is distinguished by the composition of the reference samples of alanine, glycine, hydroxyproline, and proline. Moreover, in the first group, the second main component differs from the references (egg, upper box), characterized by the content in Asp and Leu, and the milk (lower box), typified by glutamic acid. In the second group, glue–egg (typed by glycine) is diversified—but to a lesser extent—all falling in the upper box, from glue–milk (with a less typical amino acid content); most of them fall into the lower box.
The samples collected were placed on the Cartesian diagram of the PCA not far from the glue–egg references, differing in their peculiar content of Alanine, suggesting a combination of egg and animal glue binders in all the samples.
The same mixture of binders found in samples BB3, BB4, BB5, and BB6 (Table 3) suggests the use of the “a secco” technique also incorporating pigments that usually are employed in “a fresco” technique. The lipid fraction, mainly palmitic, oleic, and stearic acids, found in the samples, is probably due to egg yolk lipid content.

3.4. The Conservation Project

The “a secco” drafting of the wall paintings confirmed by microanalytical investigations, the intrinsic fragility of the pictorial film found during the fixing operation, the presence of original repaints by Biagetti only one year after the inauguration of the chapel to correct indelibly ‘stained’ surfaces (still visible), has led to an approach of extreme prudence in dealing with the cleaning of wall paintings. An approach of ‘minimum intervention’ underpinned our work, aimed at surface-level cleaning, followed by the removal of copious surface deposits resulting from a lack of maintenance, first, for the degraded state and then of the pictorial film itself. This process was undertaken with acceptance of the “historical instance” of the work, far from any claim of restoring the pictorial decoration to its “original splendor”—an unfortunate expression that often accompanies the promotion of a restoration intervention. An initial delicate and timely removal of the copious deposits of atmospheric particulate matter with very-soft-bristle retouching brushes, in tandem with the treatability of the pictorial surfaces—color decohesion, ripples, lifts, exfoliation/curls of pictorial film—was undertaken as part of the progressive reparative intervention. Once an optimal level of cohesion/adhesion of the pictorial film was restored and the unsafe plaster detachments were consolidated, the surface cleaning was carried out gradually, balancing the areas characterized by a greater graying more interpenetrated within the pictorial surfaces: a ‘dry’ methodology was used, i.e., sponges in special compact and vulcanized latex, at a neutral pH, able to absorb “dirt”. This conservative intervention has made it possible to recover and enhance the defining techniques of the divisionism style adopted by Biagetti for the decoration of the chapel (Figure 7).

4. Conclusions

The present study aimed to analyze the wall paintings of the III chapel dedicated to the Fallen of the Great War in the Cathedral Basilica of Parma, Italy. The chapel was painted in the two-year period of 1921–1922, by the painter, Biagio Biagetti (Porto Recanati, 1877–Macerata, 1948).
The aim was to understand the techniques of the painter and the state of conservation of the wall paintings, in order to contribute to the conservation project in its various phases.
Raman spectroscopy results showed that, along with classical pigments, modern pigments (or dyes) were present in almost all samples. Some were inorganic, copper (II) stannate and copper (II) arsenate. Many, however, were organic, belonging to the azo dye class. It is very likely that during the first post-war period, many synthetic pigments were abandoned or changed in formulation, and this makes it difficult to recognize them compared to current dyes.
The presence of lipid materials and protein materials was established by GC/MS investigations. The lipid fraction is not attributable to the presence of drying oils. In all four samples examined, the proteinaceous fraction has to be attributed to the presence of a combination of egg and animal glue. This result indicates that these 20th century wall paintings were made using the “a secco” technique, using a proteinaceous binder, confirming the visual impressions of the restorer.
With regard to the chemical composition of the mortar, it is compatible with an air lime obtained from a calcium carbonate mixed with clay.
During the conservative intervention, the removal of spurious deposits from the pictorial surfaces has made it possible to recover and enhance the particular executive technique of the divisionism style adopted by Biagetti for the decoration of the chapel—the more-or-less tight drafting of the countless brushstrokes with tones and colors not fused into each other, with a multidirectional trend based on the background and figure/architecture, contributing to the implementation of the different vibration of light through which the image is built, to which the refined texture of the preparatory plaster also contributes.

Author Contributions

Conceptualization, A.C. and L.B.; methodology, L.B. and A.C.; validation A.C. and S.S.; formal analysis L.B., A.C., and C.G.; investigation, L.B., A.C., and C.G.; resources, A.C.; data curation, L.B.; A.C., S.S., and C.G.; writing—original draft preparation, A.C. and L.B.; writing—review and editing A.C. and C.G.; visualization, A.C.; supervision, A.C. and L.B. All authors have read and agreed to the published version of the manuscript.

Funding

This research was supported by NextGenerationEU—Italian Ministry of University and Research, National Recovery and Resilience Plan (NRRP); Project “Ecosystem for Sustainable Transition in Emilia-Romagna (Ecosister)”; Project code ECS00000033.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The authors confirm that all data of this study are available within the article.

Acknowledgments

This research was supported by NextGenerationEU—Italian Ministry of University and Research, National Recovery and Resilience Plan (NRRP); Project “Ecosystem for Sustainable Transition in Emilia-Romagna (Ecosister)”; Project code ECS00000033. Project title: Innovative cleaning proposals for the conservation of polychrome works of art. This work has benefited from the equipment and framework of the COMP-R Initiative, funded by the ‘Departments of Excellence’ program of the Italian Ministry for University and Research (MUR, 2023–2027). The authors thank Pier Paolo Lottici and Danilo Bersani (Department of Mathematical, Physical and Computer Sciences, University of Parma) for their useful suggestions. The authors thank Andrea Comelli (Department of Chemical Science, Life and Environmental Sustainability, University of Parma) for having created the stratigraphic sections of two samples containing mortar, used for this study, and Luca Barchi (Department of Chemical Science, Life and Environmental Sustainability, University of Parma, Italy) for having had an active part in the sampling phase of the pictorial material and in the SEM/EDS analyses. The authors thank Sergio De Iasio (Department of Chemical Science, Life and Environmental Sustainability, University of Parma) for his help in processing the chromatographic results.

Conflicts of Interest

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

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Applsci 13 07235 g001 550
Figure 1. (a) Image of the east wall before restoration; (b) detail of the pervasive paint film exfoliation of the area highlighted in (a).
Figure 1. (a) Image of the east wall before restoration; (b) detail of the pervasive paint film exfoliation of the area highlighted in (a).
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Figure 2. Raman spectra of some compounds found on the painting samples. BB1—ultramarine blue; BB2—baryte; BB11—cerulean blue, gypsum, calcite, carbon (indicated by asterisk); BB12—Permanent Yellow 65, baryte.
Figure 2. Raman spectra of some compounds found on the painting samples. BB1—ultramarine blue; BB2—baryte; BB11—cerulean blue, gypsum, calcite, carbon (indicated by asterisk); BB12—Permanent Yellow 65, baryte.
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Figure 3. SEM- images in BSE of the cross-section of BB7 (a) and BB8 (c) samples; EDS analysis collected on the areas 1 and 4 of the BB7 (b) and BB8 (d) samples.
Figure 3. SEM- images in BSE of the cross-section of BB7 (a) and BB8 (c) samples; EDS analysis collected on the areas 1 and 4 of the BB7 (b) and BB8 (d) samples.
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Figure 4. FTIR spectrum of BB6 sample: c—calcite; g—gypsum; q—quartz; b—ultramarine blue; p—proteinaceous material.
Figure 4. FTIR spectrum of BB6 sample: c—calcite; g—gypsum; q—quartz; b—ultramarine blue; p—proteinaceous material.
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Figure 5. GC/MS chromatogram of the proteinaceous fraction of BB3 sample (dark-green sample taken from cypresses, exfoliated brushstroke, west wall). Ala—alanine; Gly—glicine;Thr—threonine; Ser—serine; Val—valine; Nval—norvaline (internal standard); Leu—leucine; Nleu—norleucine (internal standard); Pro—proline; Hyp—hydroxyproline; Asp—aspartic acid; Glu—glutamic acid; Phe—phenylalanine.
Figure 5. GC/MS chromatogram of the proteinaceous fraction of BB3 sample (dark-green sample taken from cypresses, exfoliated brushstroke, west wall). Ala—alanine; Gly—glicine;Thr—threonine; Ser—serine; Val—valine; Nval—norvaline (internal standard); Leu—leucine; Nleu—norleucine (internal standard); Pro—proline; Hyp—hydroxyproline; Asp—aspartic acid; Glu—glutamic acid; Phe—phenylalanine.
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Figure 6. PCA score plot of the relative percentage content of eight amino acids in 43 reference samples and samples, BB3, BB4, BB5, and BB6. The first two principal components, PC1 and PC2, account for 56.66% and 21.38% of the total variance, respectively. (G—animal glue; M—milk; E—egg; GE—animal glue and egg; GM—animal glue and milk; EM—egg and milk).
Figure 6. PCA score plot of the relative percentage content of eight amino acids in 43 reference samples and samples, BB3, BB4, BB5, and BB6. The first two principal components, PC1 and PC2, account for 56.66% and 21.38% of the total variance, respectively. (G—animal glue; M—milk; E—egg; GE—animal glue and egg; GM—animal glue and milk; EM—egg and milk).
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Figure 7. Detail of the East wall, before (a) and after (b) restoration.
Figure 7. Detail of the East wall, before (a) and after (b) restoration.
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Table
Table 1. The collected samples (BB1 to BB12), their color and description.
Table 1. The collected samples (BB1 to BB12), their color and description.
BB1 BlueBB2 OrangeBB3 Dark green
Applsci 13 07235 i001Applsci 13 07235 i002Applsci 13 07235 i003
Sky; south sail vault “Prudentia”.Weaving decoration, right rib, south sail vault.Cypresses, exfoliated brushstroke, west wall.
BB4 Dark GreyBB5 RedBB6 Grey-violet
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Exfoliated/decohesive material, central scene column, east wall.Decorated area under left window, south wall.Exfoliated material on the shoulder of first left soldier. Left scene, east wall.
BB7 MortarBB8 MortarBB9 Red
Applsci 13 07235 i007Applsci 13 07235 i008Applsci 13 07235 i009
Mortar, with pictorial film, right edge of the window on the left, south wallMortar, with pictorial film, crown of thorns above right scene, east wallLeft angel, south wall.
BB10 PinkBB11 BlueBB12 Yellow
Applsci 13 07235 i010Applsci 13 07235 i011Applsci 13 07235 i012
Above left angel, south wall.Sky right side of the bezel, east wall.Day attachment contour on the right, south wall.
Table
Table 2. Main features observed in Raman spectra of wall painting fragments.
Table 2. Main features observed in Raman spectra of wall painting fragments.
Wavenumbers (cm−1)Assigned SpeciesSamplesReference
224, 245, 291, 411, 611, 660Haematite [Fe2O3]BB1, BB2, BB5, BB10[37,38,39,40]
207, 465Quartz [SiO2]BB5[37,38,39,40]
463, 988Baryte [BaSO4]BB2, BB4, BB9, BB12[37,38,39,40]
415, 1008Gypsum [CaSO4·2(H2O)]BB2, BB4, BB5, B11[37,38,39,40]
155, 281, 711, 1085Calcite [CaCO3]BB5, BB6, BB9, BB10, BB11[37,38,39,40]
1584GraphiteBB10[41]
1320, 1590CarbonBB2, BB3, BB4, BB5, BB6, BB10[41]
258, 548, 1096Ultramarine blue [Na7Ca(Al6Si6O24)]BB1, BB6[42,43]
868Copper (II) arsenate [Cu2(AsO4)(OH)n]BB1, BB3[44]
992, 1089, 1188, 1217, 1341, 1452, 1483Naphtol pigment (PR8?) [C24H17ClN4O4]BB9[35,38,45,46,47]
987, 1098, 1218, 1467, 1598, 1622Monoazo-pigmentBB6[35,38,45,46,47]
537, 673Cerulean blue [CoO.nSnO2]B11[42,46]
1285, 1433, 1083, 1570Naphtol pigment (PR112?)
[C24H16Cl3N3O2]		BB12[35,38,45,46,47]
1139, 1218, 1340, 1489, 1623Pigment Yellow 1 (PY1) C17H16N4O4BB12[35,38,45,46,47]
790, 950, 1136, 1326, 1392, 1487, 1535, 1623, 1670Permanent Yellow 65 (PY65) C18H18N4O6BB12[35,38,45,46,47]
Table
Table 3. Pigments and binders detected by Raman spectroscopy, FTIR and GC/MS in the collected samples, BB1 to BB12.
Table 3. Pigments and binders detected by Raman spectroscopy, FTIR and GC/MS in the collected samples, BB1 to BB12.
BB1 Blue
Pigments: ultramarine blue, haematite, copper (II) arsenate		BB2 Orange
Pigments: gypsum, haematite, baryte, carbon		BB3 Dark green
Pigments: copper (II) arsenate, carbon
Organic binders: egg and animal glue.
BB4 Dark Grey
Pigments: carbon, gypsum, baryte
Organic binders: egg, animal glue, arabic gum.		BB5 Red
Pigments: carbon, gypsum, haematite, quartz, calcite.
Organic binders: egg, animal glue.		BB6 Grey-violet
Pigments: carbon, calcite, gypsum, monoazo pigment, ultramarine blue
Organic binders: egg, animal glue.
BB7 Mortar
Binder: lime, calcium carbonate, clays		BB8 Mortar
Binder: lime, calcium carbonate, clays Pigments: baryte		BB9 Red
Pigment: naphtol pigment (PR8?), baryte, calcite
BB10 Pink
Pigments: carbon, calcite, haematite, grafite		BB11 Blue
Pigments: calcite, anhydrite, cerulean blue		BB12 Yellow
Pigments: baryte, pigment yellow 1, naphtol pigment (PR112?), Permanent Yellow 65.
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Bergamonti, L.; Graiff, C.; Simeti, S.; Casoli, A. The 20th Century Wall Paintings in the Chapel of the Fallen in Parma Cathedral (Italy): Scientific Investigations for a Correct Conservation Project. Appl. Sci. 2023, 13, 7235. https://doi.org/10.3390/app13127235

AMA Style

Bergamonti L, Graiff C, Simeti S, Casoli A. The 20th Century Wall Paintings in the Chapel of the Fallen in Parma Cathedral (Italy): Scientific Investigations for a Correct Conservation Project. Applied Sciences. 2023; 13(12):7235. https://doi.org/10.3390/app13127235

Chicago/Turabian Style

Bergamonti, Laura, Claudia Graiff, Silvia Simeti, and Antonella Casoli. 2023. "The 20th Century Wall Paintings in the Chapel of the Fallen in Parma Cathedral (Italy): Scientific Investigations for a Correct Conservation Project" Applied Sciences 13, no. 12: 7235. https://doi.org/10.3390/app13127235

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