This work aims to investigate the correlation between the painting materials used by Picasso to create four artworks in Barcelona in 1917 and their actual conditions. Specifically, a range of crack types and patterns was observed in the painted layers. The paintings, kept together in Picasso’s family house until they were donated to the Museu Picasso in 1970, had significant differences in their condition, even though they present several similarities in the choice of materials, technique and in their conservation history. A multi-analytical approach was adopted to characterise the painted layers by X-ray fluorescence spectroscopy, fibre optic reflectance spectroscopy in the 350–2200 nm range, gas chromatography-mass spectrometry, and Fourier transform infrared spectroscopy. The obtained results have been combined with those from a previous analytical campaign focused on the study of grounds and canvases of these four paintings and with visual examination of the cracks to establish hypotheses about the differences in degradation. This combined overview of non-invasive documentation techniques, chemical analysis and observations of the mechanical damage has provided an insight into the possible contribution each layer could have played in the damage observed in the four canvas paintings.
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This research presents results obtained by a multi-analytical study on the composition of paint layers in four paintings created by Pablo Picasso in Barcelona in 1917, now belonging to the Museu Picasso, compared to a descriptive analysis on the cracks observed.
The paintings, namely Seated Man (MPB110005; 104 × 54 cm), Man with Fruit Bowl (MPB110006; 100 × 70 cm), Woman on an Armchair (MPB110007; 92 × 64 cm), and Blanquita Suárez (MPB110013; 73 × 47 cm), have a range of crack types and patterns in the painted layers. This paper brings together the results of a previous analytical campaign performed on the grounds and canvases used by Picasso and the latest study on the paint films of the selected paintings in an attempt to shed some light on the relationship between the choice of the materials, environment conditions, failure mechanisms, and degradation patterns. The main aim was to determine whether differences in the composition of the paints could have contributed to the variation in degradation shown by each painting.
The selected paintings were created during Picasso’s stay in Barcelona (June–November 1917) in a cubist style. In this period, Picasso often worked in Rafael Martinez Padilla’s studio. This aspect is of utmost relevance. The existing documentation indicates that Picasso did not have his own studio; therefore, he did not re-use any canvas (as he commonly did) and had to purchase all the painting materials including canvases, brushes, turpentine and oil paints. This could explain the narrow palette used, limited to seven colours (white, black, brown, red, yellow, green and blue) plus two more colours resulting from their combination (grey and beige). Given the geometric and colour similarities, these four paintings represent a series within the group of 11 paintings created in Barcelona in 1917, leading to this comparative study. When Picasso returned to Paris, the paintings were stored in his family house until they were donated to the Museu Picasso in Barcelona in 1970, the institution that still owns the works <1,2,3> (Fig. 1). One final aspect relevant to the selection of these case studies is that the paintings are mounted on the original stretchers and no evidence of conservation treatments prior to this donation has been found. In 2016 the museum noticed the need to consolidate only one of the paintings, namely Seated Man, due to extensive cracking and fear of paint loss.
Woman on an Armchair at Picasso’s family house. Casa Vilató (Passeig de Gracia, 48, s/d, Barcelona). Fotografia de J. Francès Estorch. Fons Joan Vidal Ventosa, Museu Picasso, Barcelona.
Considering that paintings are complex, heterogeneous, multi-layered, and dynamic systems, identifying the composition and material properties of the different layers of a painting is critical in the understanding of degradation processes and products as well as their interactions <6, 8>. A previous study by the authors focused on the relationship between the composition and the physical–mechanical properties of painting support materials (canvases and the ground layers) used by Picasso in the four paintings <4>. The results had showed that, in all cases, the artist painted on cotton canvases and applied two ground layers. The organic composition of the grounds mainly consisted of animal glue, mixed with small amounts of drying oils and polysaccharide compounds. In the four paintings, the bottom ground layer was richer in binding media than the upper one. In particular, the upper ground layer of Man with a Fruit Bowl was mainly composed of a zinc (Zn)-containing compound, whereas the upper ground layer in the three other paintings was mainly composed of lead white and other materials including calcite. This had probably caused the slight differences in the tone of the four ground layers, ranging from grey to orange tinges. The previous work already addressed some hypotheses about the difference in crack patterns observed in the paintings (Table 1) charline-picon.comed to the presence of either Zn or lead (Pb) in the grounds <7>, the amount of animal glue in ground layers, and the degree of tightness in the canvas weave <4,5,6>.
In this study, a multi-analytical study was carried out to study the colour palette of the four paintings, prioritizing the use of non-invasive techniques such as in-situ X-ray fluorescence spectroscopy (XRF) and fibre optic reflectance spectroscopy (FORS). Moreover, a small number of micro-samples from each painting was analysed by optical microscopy (OM) and gas chromatography-mass spectrometry (GC–MS). Micro-Fourier transform infrared spectroscopy (µ-FTIR) analysis was also performed, when there was a sufficient amount of remaining sample. In this way, the results obtained through elemental analyses were combined with the spectroscopic and chromatographic results, allowing the identification of the palette and the binding media used by the artist.
In situ elemental analysis was performed non-invasively with portable Elio X-ray fluorescence equipment by XGlab X and Gamma Ray Electronics, which has been successfully applied on modern and contemporary paintings <8>. The paint examination was performed directly on the surface of the areas marked in Fig. 2. The analysis was carried out in air, with a sample area of 1 mm diameter, 100 s acquisition live-time at 40 kV and 100 μA, using an Rh-target without filtration.
A small number of micro-samples from the painted layers of the four artworks were collected to identify the inorganic and organic binding media. The samples were analyzed by micro-Fourier transform infrared spectroscopy (µ-FTIR) in attenuated total reflectance (ATR) and transmittance mode with a Thermo Fisher Scientific Nicolet iN10 MX Ultra Fast Motorized stage with MCT Detector. The spectra were acquired between 4000 and 600 cm−1, 128 scans, with a resolution of 4 cm−1.
The organic binding media was also analysed by GC–MS using an Agilent 6890NGC instrument with a capillary HP-5 (5%-phenyl)-methylpolysiloxane column (30 m, 0.25 mm, 0.25 µm), interfaced with an Agilent 5973NetworkMS. The temperature programme was set from 80 °C to 315 °C, 10 °C/min. The MS was run in FullScan mode (m/z 50–600), 1.9 scans/s. The transfer line was at 280 °C and the source temperature was 150 °C. Electron ionisation energy was 70 eV. Quantitative GC–MS analysis was performed using nonadecanoic acid as the internal standard. The paint samples were transestherified using (trifluoromethylphenyl)trimethylammonium hydroxide (2.5% in methanol), overnight reaction as described in <9,10,11>. The following molar ratios between the most significant fatty acids were calculated: palmitic to stearic acid (P/S), azelaic to palmitic acid (A/P), oleic to stearic acid (O/S) and azelaic to suberic acid (A/Sub) ratios, as reported also in . The obtained data were compared to previous results obtained by the authors on twentieth century artists oil paints as described in <11,12,13>.
For image processing, the areas homogeneous in colour were defined and for each of them the contour lines were first processed, trying to enhance the differences between light and dark areas. Then, the images were desaturated (in grayscale), modifying the references "black" (0) and "white" (255) to highlight the cracks.
Table 1 gives an overall description of the crack patterns observed in the four paintings. As mentioned, different degradation phenomena were observed in the paintings.
Even though all the paintings had been stored in the unstable environment of the same house, only the painting Seated Man showed such extensive damage. The fact that the cracks were over the entire surface but less pronounced in areas protected by the stretcher bar along the edge, suggests that the damage was environmentally induced. If this is the case, the interesting question is why the other three paintings do not show the same degree of damage. One explanation may be that the composition of materials is different and therefore caused this painting to be more affected by the ambient environment.
In this section, the results for the pigments and binders of different paints from the four paintings are presented. Considering the previous study of the canvas supports and ground layers <4>, this multi-analytical study is intended to identify the composition and condition of the paint film, as well as to investigate if the paint layer could have had any impact in the cracks observed in the four paintings.
XRF and FORS are non-invasive, effective, and rapid methods to determine the tentative pigment composition <18,19,20>. This section describes all possible pigments detected in the painted areas and Table 2 gives the results for each specific painting.
XRF analysis on the four paintings showed that Pb was the main element in the white painted layers, suggesting the presence of the basic lead (II) carbonate, lead white (2PbCO3·Pb(OH)2). This was also confirmed by FORS and FTIR results (due to the characteristic IR bands at 1450 nm as well as at around 3530,1390 and 680 cm−1). In some white areas, barium (Ba) was also detected, more probably as barite (barium sulphate, BaSO4) used as a filler mixed with lead white. In other white areas, XRF results revealed Zn and Ba, which could be associated with the presence of lithopone or the presence of barite and a zinc-based compound. FORS and XRF found lead white also in the grey and beige hues. Moreover, in two of the three beige painted areas, an iron (III) hydroxide-oxide-based pigment was identified <21, 22>. Similarly, in the grey areas of two paintings, FORS found iron oxides. XRF identified relatively low amounts of silicon (Si) and possibly titanium (Ti) in some grey areas, where FORS identified the presence of alumino-silicates, due to the presence of very weak absorption bands in the 1380–1420 nm range that could be related to the first overtones of the hydroxyl stretching vibration mode. The presence of titanium could be related to impurities of earth pigments <23>.
In one case, Woman on an Armchair, the bluish-grey paint was tentatively identified by FORS as a mixture of a carbon-based pigment and ultramarine blue (3Na2O.3Al2O3.6SiO2.2Na2S). This blue pigment was detected by FTIR as well, due to the peculiar absorptions at around 970, 690, 650, and 580 cm−1. Its presence could explain the grey tone of the paint.
Regarding the black pigments used in three of the four paintings, the presence of calcium (Ca) and phosphorous (P) is likely associated with the use of an ivory or bone black pigment (Ca3(PO4)2 + CaCO3 + carbon (C)) as the main black pigment. Moreover, iron-based pigments were also detected in some of the black areas. It was not possible to perform FTIR analysis to corroborate this finding.
In the red and brown areas analysed, iron (Fe) and mercury (Hg) were the main elements detected by XRF. This indicated a mixture of an iron (III) oxide-based pigment, such as Mars red, and vermillion (both confirmed by FORS).
Yellow and green pigments were present only in Man with a Fruit Bowl and Blanquita Suarez and mainly contain chromium (Cr). The presence of Cr in green areas was related to the viridian pigment (Cr2O3.2H2O) as found by FORS. Viridian, more transparent and vivid than the chrome oxide green pigment, was also used in the time period and was stable (18). Strontium (Sr) and Fe were also detected in Man with a Fruit Bowl in some of the yellow and green areas analysed, indicating the presence of strontium yellow (SrCrO4) and iron-based compounds. Commercially, strontium yellow (strontium chromate) was often mixed with other pigments, such as Prussian blue (Fe4
Blue areas were observed only in Blanquita Suárez. These resulted to contain a mixture of compounds containing Zn, Zn oxide and/or Zn sulphide, and a blue pigment. The blue pigment was identified as ultramarine blue by FORS and also in previous research by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM–EDX) on a cross-section from the same area of the painting <25>. This finding was also corroborated by FTIR analysis. Ultramarine blue was also tentatively identified by FORS in some of the grey areas of Woman on an Armchair.
As reported in Table 2, FTIR and GCMS analysis of micro-samples showed that the examined paints were bound in lipid media. The IR spectra showed the typical absorptions due to the presence of lipid-based binding media, in particular those at 2921, 2850 (stretching–CH2CH3), 1729, 1708 (stretching C = O) and 1166 cm−1 (stretching C-O) <26>.
GCMS results provided further details about their composition according to the fatty acids profile. Table 2 lists the GCMS results and reports the ratios between azelaic-to-palmitic acid (A/P), oleic-to-stearic acid (O/S) and palmitic-to-stearic acid (P/S) and azelaic-to-suberic acid (A/Sub) which are generally used for the characterisation of drying oils <11, 27,28,29>.
All the analysed paint samples from Seated Man, Man with a Fruit Bowl, and Woman on an Armchair were characterised by the typical composition of a polymerised drying oil paint, with saturated mono-saturated fatty acids (mirystic acid, lauric acid, palmitic acid, stearic acid), di-fatty acids (azelaic acid, suberic acid, sebacic acid), and traces of unsaturated oleic acid <30,31,32>. The calculated A/P ratios were generally higher than 3 which indicated a high degree of oxidation: azelaic acid, in fact, is the most abundant product formed upon oxidation and polymerisation of unsaturated fatty acids present in fresh drying oils. In the same way, the O/P ratios were in all cases lower than 0.1, suggesting that the lipid networks were well polymerised and only very low amount of unsaturated oleic acid was still present. In this sense, the presence of lead-based compounds, detected both in ground layers <4> and in the pigments from the painted layers (see XRF, FORS and FTIR results in Table 2), may have catalysed the polymerisation and the oxidation processes.
Although the identification based only on the P/S ratios is not always completely reliable for modern and contemporary oil paints <11, 13,14,15,16,17>, some indications about the type of oils can be provided. The brown paints, having P/S ratios values ranges between 1.8 and 1.9, were likely bound in linseed oil. For the whites, due to the calculation of P/S ratios and the identification of specific fatty acids (arachidic and behenic acids), safflower and/or sunflower oils and poppy seed oils were likely detected in Man with a Fruit Bowl and Woman on an Armchair, respectively. These findings concur with specific literature reporting that, in general, white and blue pigments were bound in poppyseed, safflower and sunflower oils, to avoid yellowing occurring in linseed oil during curing <33,34,35>. According to the obtained A/Sub ratio <29>, the presence of a pre-heated linseed oil was identified in Seated Man: only in this case, in fact, the A/Sub value was 1.4, referring to a pre-treatment by cooking or boiling the vegetable oil.
The red paint in Blanquita Suárez was bound in linseed oil. The white paint appeared to be a mixture of drying-semi-drying oils (safflower and sunflower oils, as seen for other white paints) containing phthalic acid and glycerol in a high amount. An explanation for the presence of this compound has not yet been determined: phthalic acid is indeed a very common environmental contaminant and not necessarily a paint constituent, but its significant presence could be related to the use of an alkyd-based compound. However, this needs further research as alkyd paints were introduced into the art market only later in the 1930s <36,37,38,39,40>.
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Another important consideration related to the organic fraction is the detection of carboxylates, also known as metal soaps. In particular, lead soaps were observed due to the typical FTIR absorption peak at around 1530 cm−1: these carboxylates had likely formed as products after the reaction of metal ions (from lead white pigment) and the carboxylic acids after hydrolysis of the fatty acid moieties in the triglycerides of drying oils <41>. That the formation of metal carboxylates has strong implications for the conservation of twentieth century paintings is well known and, thus, further research is needed to monitor eventual conservation problems which could occur in Picasso paintings.