A multianalytical study of oil binding media and pigments on Bohemian Panel Paintings from the first half of the 14th century

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Original article

A multianalytical study of oil binding media and pigments on Bohemian Panel Paintings from the first half of the 14th century ˇ u˚ a,∗ , Václav Pitthard b,1 , Stˇ ˇ epánka Chlumská a,2 , Ivana Turková c,3 Radka Sefc a

The National Gallery in Prague, Staromˇestské nám. 12, 110 00 Prague, Czech Republic Kunsthistorisches Museum Wien, Burgring 5, 1010 Vienna, Austria c Prague Institute of Criminalistics, Bartolomˇejská 12, 110 00 Prague, Czech Republic b

a r t i c l e

i n f o

Article history: Received 17 February 2016 Accepted 3 October 2016 Available online xxx Keywords: Oil binding media Bohemian panel paintings Gas chromatography/mass spectrometry Micro-Raman spectroscopy Pigment identification Medieval period

a b s t r a c t This paper deals with the results of a broad-based survey of both the binding media and the pigments used during the first half of the 14th century on Bohemian panel paintings from the collections of the National Gallery in Prague. The work is focused on the specific use of oil binding media and pigments in the workshop of the Master of the Vyˇssˇ í Brod Cycle, the most important painter in the period around the 1340s in Bohemia. Extensive laboratory examinations of the micro-samples were executed by means of optical microscopy (OM), scanning electron microscopy with an energy-dispersing detector (SEM/EDS), microRaman spectroscopy (MRS), histochemical staining (HS) and gas chromatography/mass spectrometry (GC/MS). The data obtained by the multianalytical approach pointed out that the oil binding medium was used as the principal medium within colour paint layers in the Bohemian panel paintings as early as around 1340–1350. This unique identification of oil binding media opens new possibilities for the interpretation of the painting technique in Central Europe in the 14th century. © 2016 Elsevier Masson SAS. All rights reserved.

1. Introduction This paper presents the results of scientific research into the painting technique of the Vyˇssˇ í Brod Cycle (Master of Vyˇssˇ í Brod Cycle, Prague, around 1345–1350), one of the most important Gothic monuments of Bohemian provenance (Fig. 1). The nine panel paintings (Table 1), ordered by a leading nobleman of the Luxembourg Court, Peter I of Roˇzmberk (Rosenberg), is named according to its provenance in the Monastery Church of the Assumption of Our Lady in Vyˇssˇ í Brod (the owner is the Cistercian Abbacy in Vyˇssˇ í Brod, on a long-term loan to the National Gallery in Prague, inv. nos. VO 13504-13512, canvas-covered maple wood, size: 99 or 99.5 × 91–93.5 cm) [1]. The cycle was ascribed to an anonymous painter, helpfully described as the Master of the Vyˇssˇ í Brod Cycle (or Altarpiece) [2]. This anonymous Master was active with his workshop in Prague before the middle of the 14th century. The workshop

∗ Corresponding author at: The National Gallery in Prague, Convent of St. Agnes of ´ 17, 110 15 Prague, Czech Republic. Tel.: +420221879255. Bohemia, U Milosrdnych ˇ u), ˚ [email protected] E-mail addresses: [email protected] (R. Sefc ˇ Chlumská), [email protected] (V. Pitthard), [email protected] (S. (I. Turková). 1 Tel.: +431525245702. 2 Tel.: +420221879247. 3 Tel.: +420974824315.

was active in the court circle of the Bohemian King and later Roman Emperor Charles IV (1316–1378) at a time when Prague, thanks to its ruler, was gradually becoming an important European cosmopolitan metropolis. In specialist literature there is no general agreement on the settling of questions concerning the original provenance and reconstruction of the Vyˇssˇ í Brod Altarpiece as a whole [3]. Authors do agree, however, that more than one painter participated in its creation under the guidance of the main Master (identified with the Master of the Vyˇssˇ í Brod Cycle). In spite of the unifying workshop characteristics the co-workers differ to a varying extent from the style of the main Master. Specialised investigation, both from the viewpoint of the study of art and from that of the restorer, usually consider the Master’s work to have been the paintings of The Annunciation, The Nativity, The Adoration of the Magi and The Resurrection; then there is the group consisting of the paintings of Christ on the Mount of Olives, The Crucifixion and The Lamentation. Considered the least close to the style of the main Master, who was acquainted with contemporary North Italian and French painting, are the pictures of The Descent of the Holy Spirit and The Ascension of Christ. There are evident differences in the composition of the area of the painting, the physiognomy of the figures and the execution technique. Older literature claimed links between the Master of the Vyˇssˇ í Brod Cycle and his workshop circle and North Italian painting (Venice, Florence, Siena, Bologna). Characteristics are the layered construction

http://dx.doi.org/10.1016/j.culher.2016.10.003 1296-2074/© 2016 Elsevier Masson SAS. All rights reserved.

ˇ u, ˚ et al., A multianalytical study of oil binding media and pigments on Bohemian Panel Paintings Please cite this article in press as: R. Sefc from the first half of the 14th century, Journal of Cultural Heritage (2016), http://dx.doi.org/10.1016/j.culher.2016.10.003

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Fig. 1. Nativity (owner the Cistercian Abbacy in Vyˇssˇ í Brod, on a long-term loan to the National Gallery in Prague, In. No. VO 13504), Photo © 2016 The National Gallery in Prague.

of the flesh areas with the aid of brownish-green under-painting [4] and the techniques used for the decoration of the gilded surfaces [5,6]. Italianisms are also evident in some of the composition [7] and iconographic motifs (Giotto, Duccio) [2,3]. The restoration of the panel paintings greatly advanced knowledge of the painting technique. In particular, the first comprehensive modern restoration of all the panels took place in the years 1951–1954, which was followed by the second restoration campaign between years 1993–2007. During this latter restoration micro-samples of the paints were taken for the material investigation of individual panels. The first results of the scientific investigations carried out in the laboratory of the National Gallery in Prague in 1998 were based on findings using optical microscopy, micro-chemical tests and scanning electron microscope with an energy dispersive X-ray spectrometer. The results of these measurements revealed a significant presence of the oil-containing binder in the paint layers of the panels [8], although in the period of the mid-14th century egg tempera was the most widespread painting technique, which continued right into the 15th century. The painting style of the Bohemian panels strongly corresponds the Italian influence, namely in the choice and use of pigments, and therefore, the analytical results gained about the binding media raised the question whether the oil medium was indeed applied in the individual paint layers. To deepen the knowledge of the painting technique it was necessary to address these concerns, and for these reasons, a set of samples was selected within the framework of the recent investigations. The newly available instrumental techniques, namely gas chromatography for the analyses of binding media and Raman spectroscopy for the identification of inorganic

materials, were applied to verify and add further information with a view to the possibilities of comparison among the individual layers of the painting as well as among the individual panels. Based on such complete scientific research it was then possible to contribute to the discussion concerning the precise identification of individual materials and to technological questions regarding the consideration of differences in the painting technique of the main Master and the workshop assistants. 2. Experimental 2.1. Sampling of medieval panel paintings Paint samples were acquired during restoration treatments of individual panels from 1998 [8] till the latest restoration done in 2013. Micro-samples were simultaneously analysed during these restoration interventions and recently, in 2014–2015, they were selectively revised and classified for further analytical investigations. The analyses concentrated on samples of the blue colours (the reverse of Christ’s cloak, the cloak of the Virgin Mary) and samples taken from the flesh areas, as well as selectively on other colour layers (yellow, green and red paint). The sampling details are listed and described in Table 1. The analyses were approached with several analytical methods using optical microscopy [9], micro-Raman spectroscopy [10–12], histochemical staining [13] and gas chromatography with mass spectroscopy [14,15]. Furthermore, the detailed elemental analysis of pigments was performed using a scanning electron microscope

ˇ u, ˚ et al., A multianalytical study of oil binding media and pigments on Bohemian Panel Paintings Please cite this article in press as: R. Sefc from the first half of the 14th century, Journal of Cultural Heritage (2016), http://dx.doi.org/10.1016/j.culher.2016.10.003

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Table 1 List of the investigated samples of the flesh tones, blue and green areas of painting and analyses performed. Inv. No.

Painting

Sample

Sampling position

VO 13504

Annunciation

VO 13505

Nativity

VO 13506

Adoration of the Magi

VO 13507

Christ on the Mount of Olives

99-39-5 99-39-6 99-40-3 99-40-5 99-40-9 99-41-1 99-41-2 99-41-9 98-88-1 98-88-2 98-88-3 98-88-5 98-88-11 05-33-1 05-33-2 05-33-3 05-33-4 05-33-7 06-39-1 06-39-2 06-39-3 06-39-6 06-39-8 03-54-1 03-54-2 03-54-5 13-94-6 07-48-4 07-48-6 07-48-7 07-48-11 07-48-12

Blue cloud Green rocky ground Blue cloak Blue cup of St Joseph Flesh of old women Blue cloud Blue robe of Virgin Mary Flesh of Virgin Mary Flesh of Christ (light) Flesh of Christ (shadow) Flesh on the hand Green cloak of St. John Blue reverse side of the cloak Flesh of Virgin Mary Blue robe of Virgin Mary Blue cloak of Virgin Mary Green cloak St. John’s forehead Flesh of St John Flesh of St Magdalene Flesh of St Joseph Green cloak of St. John Blue reverse side of the cloak Flesh of assistance figure Blue cloak Wing of angel Blue reverse side of sleeve Blue reverse side of the cloak Flesh of the face St. John’s forehead Blue cloud Blue cloak

NG

VO 13508

VO 13509

Crucifixion

Lamentation

VO 13510

Resurrection

VO 13511 VO 13512

Ascension Descent of the Holy Ghost

Analyses performed OM

EDS

MRS

+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +

+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +

+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +

HS

GC/MS

+

+

+ + + +

+ +

+

+

+ + +

+ + +

+ +

+ +

+ +

+

NG: The National Gallery in Prague; OM: optical microscopy; EDS: scanning electron microscope with an energy dispersive X-ray spectrometer; MRS: micro-Raman spectroscopy; HS: histochemical staining; GC/MS: gas chromatography/mass spectrometry.

(SEM) coupled with an energy dispersive X-ray spectrometer (EDS) [16]. The combination of GC/MS techniques and histochemical staining was crucial for accurate characterisation of binding media in the specific paint layer.

of 300 hours was repeated 4 times [18]. After more than 10 years stored at room temperature, the standards were then re-measured by GC/MS. 2.3. Optical microscopy (OM)

2.2. Aged reference standards (mock-ups) In parallel to the GC/MS analyses of paint samples from medieval panels, investigations on aged reference standards were also carried out. Especially to verify the questions concerning the possibility of the detection of egg-containing binding medium as well as admixtures with drying oils, a set of UV-aged drying oils and tempera reference mock-ups was additionally investigated using the GC/MS technique. Two pigmented drying oils (linseed oil and walnut oil) and two types of tempera were previously prepared in the Kunsthistorisches Museum Vienna in 2002 [17]. Temperas were prepared as follows: egg yolk was mixed with linseed oil (in ratio 1:1, v/v) and powdered pigments were slowly added to it. For the second type, egg yolk was firstly diluted with water to make an emulsion (1:3, v/v) and afterwards twenty drops of the linseed oil were mixed in and again powdered pigments were then added. Both drying oils and pigments (azurite and verdigris) were obtained from Kremer, while eggs were purchased from a local market. The paint pastes were spread on glass slides with a spatula to form a thin homogenous film, left to dry and then aged in a SOL 2 sunlight simulation chamber (Dr K. Hönle GmbH UV Technologies, Munich, Germany) equipped with a Xenon lamp, offering light equivalent to the optical spectrum of sunlight with illuminiscence of 120 000 lux and irradiation of 910 W m−2 . The reference mock-ups were kept under these conditions for a period of 300 h. The ageing sequence

The micro-sample was fixed in methyl methacrylate resin (Spofacryl, SpofaDental a.s. or Clarocit, Struers GmbH). Consideration of the stratigraphy was carried out on an Eclipse 600 Nikon polarising microscope in reflected and intersecting light, on a dark field and after excitation by UV light, Hg discharge lamp, UV filter 330–380 nm and 450–490 nm. Morphological traits of individual pigments on prepared sections were examined in intersecting polarised light in parallel (PPL) and crossed (XPL) nicols. Usual magnification was 200–1000×. Micrographs of the preparations and also of the cross-sections of real samples were made using a DS-Fi2 Nikon digital camera. 2.4. Micro-Raman spectroscopy (MRS) Molecular analysis by means of micro-Raman spectroscopy was performed on the same cross-sections using the mapping mode for better observation of individual components presented in colour layers. Raman spectra were collected by the Raman microscope Nicolet DXR (Thermo Scientific, USA) in combination with an Olympus confocal microscope with lenses 10×, 20×, 50× and 100×, equipped with a CCD camera for signal detection. Measurement took place in the range of 3300–50 cm−1 . The spectral resolution was 4 cm−1 . Two lasers were used as the excitation source with wavelengths of 532 nm (diode laser) and 780 nm (diode laser).

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Table 2 Chromatographic characteristics of the pigmented oil and tempera mock-ups. Oil and Tempera mock-up

Pigment

P/Sa

Linseed oil (Kremer)

Azurite Verdigris Azurite Verdigris Azurite Verdigris Azurite Verdigris

1.4 1.4 2.6 2.5 2.3 2.0 3.2 3.3

Walnut oil (Kremer) Egg yolk: linseed oil (1:1, v/v) Egg yolk: water (1:3, v/v) + drops of linseed oil

A/Pa ± ± ± ± ± ± ± ±

0.3 0.3 0.3 0.3 0.3 0.2 0.3 0.2

1.3 1.2 1.1 1.0 0.4 0.3 0.1 0.1

± ± ± ± ± ± ± ±

O/Sa 0.2 0.2 0.2 0.2 0.1 0.1 0.1 0.1

0.1 0.5 0.1 0.5 0.2 0.5 0.2 0.4

± ± ± ± ± ± ± ±

A/Sua 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1

6.1 5.8 7.9 7.5 3.4 3.8 3.5 3.6

± ± ± ± ± ± ± ±

Cha 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.4

– – – – Yes Yes Yes Yes

P: palmitic acid (C16:0 ); S: stearic acid (C18:0 ); O: oleic acid (C18:1 ); A: azelaic acid (2C9 ); Su: suberic acid (2C8 ); Ch: cholesterol oxidation products. a Mean values and standard deviations of peak areas of fatty acids methyl esters, three GC/MS parallel measurements of UV-aged pigmented oil and tempera mock-ups, 2015.

The performances of the lasers depended on the composition of the mixtures of pigments and on the sensitivity of the individual components of the coloured layers. The time of measurement was 1–5 minutes with the output of the lasers from 0.7 to 10 mW. The

measurement used was spot measurement directly on the particles of pigments or in the regime of surface mapping in a defined area or layer in stratigraphy. Spectra were evaluated in the Omnic 9 programme and compared with the spectra library.

Fig. 2. Cross-section of sample taken from the blue reverse coat of Christ (Christ on the Mount of Olives, 98-88-11): a, b: in reflected and ultraviolet light. On the chalk ground (1) lies two blue layers. On the under-painting is azurite (2) and on the top blue layer is applied a lapis lazuli (3). 2D mapping (c) and spectrum (d) by means of Raman spectroscopy; c: colour areas indicate presence of azurite, referential absorption band at 400 cm−1 and spectrum of the standard pigment and of the blue pigment in the blue under layer; d: colour areas indicate presence of lapis lazuli, referential absorption band at 546 cm−1 and spectrum of the standard pigment and of the blue pigment in the top blue layer. Photo © 2016 The National Gallery in Prague.

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Fig. 3. BSE image of the sample taken from the blue cloud of Annunciation (99-39-5). 2D scan mapping of relevant elements (Na, Al, Si) of the grains of lapis lazuli in the layer of azurite is also given.

2.5. Histochemical staining Histochemical colouring was carried out on cross-sections of micro-samples with the agent Fuchsin S for the identification of protein containing binders. In the presence of proteins, the layer was stained pink (fuchsia) [13]. 2.6. Gas chromatography/mass spectrometry (GC/MS) The analytical procedure for the analysis of lipids was based on the transesterification of fatty acids (0.2 M methanolic solution of Meth-Prep II reagent at 60 ◦ C for 1 hour) and the determination of their relative ratios to identify particular lipids. The analytical procedure for the analysis of proteinaceous materials is based on an acidic hydrolysis of proteins to liberate amino acids (6 M hydrochloric acid at 105 ◦ C for 24 hours), followed by the derivatisation and quantitative determination of amino acids as their silyl derivatives (MTBSTFA silylation reagent in a pyridine–pyridine hydrochloride mixture at 60 ◦ C for 1 hour). Lipid separations were performed on a DB-5 MS [poly (5% phenyl-95% methylsiloxane), J&W, USA] capillary column with 0.25 mm internal diameter, 0.25 ␮m film thickness, and 30 m length. The temperature of the oven was programmed from 50 ◦ C (1 min) to 320 ◦ C (12 min) at 10 ◦ C.min−1 for the analysis of lipids. For the proteinaceous binding media analysis the same capillary column was applied, but under a different temperature program [80 ◦ C (1 min) to 280 ◦ C (1 min) at 6 ◦ C.min−1 ]. All GC/MS analyses were performed on a 6890 N gas chromatograph connected to a quadruple mass spectrometer, model 5973 N (both Agilent Technologies, USA) [14,15,19]. 2.7. Scanning electron microscope with an energy dispersive X-ray spectrometer (SEM/EDS) The elemental analyses were carried out on a scanning electron microscope with energy-dispersing detector on the JEOL JXA 50A/EDAX instrument in the Geological Institute of the Czech Academy of Sciences. Later the JEOL 6460 equipment was used in the chemical-technological laboratory of the National Gallery in Prague and the TESCAN instrument in the laboratory of the Prague Institute of Criminalistics. Mapping analysis of the element composition on the sections was carried out on the LYRA3 TESCAN analysis unit equipped with a Si (Li) X-ray detector. The analysis took place in a high vacuum, acceleration voltage 20 kV, BSE detector. The quantitative element mapping was performed with an EDS

Bruker Quantax, ESPRIT software. The polished cross-section was prepared by applying a graphite coating. 3. Results and discussion 3.1. UV-aged oil and tempera reference mock-ups The GC/MS measurements were repeated three times for each artificially aged standard. The peak areas of selected fatty acids as their methyl esters were used for the evaluation of the procedure to identify drying oils and temperas, in particular saturated monocarboxylic acids [palmitic acid (C16:0 ) and stearic acid (C18:0 )], unsaturated monocarboxylic acid [oleic acid (C18:1 )] and dicarboxylic acids [suberic acid (2C8 ) and azelaic acid (2C9 )]. The value of the P/S ratio (palmitic acid/stearic acid) characterises the individual binding medium, while the values of A/P ratio (azelaic acid/palmitic acid) and A/Su ratio (azelaic acid/suberic acid) give an indication of whether the drying oil is present and pre-treated, respectively [18,20–22]. Values of O/S ratio (oleic acid/stearic ratio) evaluate the extent of the aging process [23]. As summarised in Table 2, the chromatographic results of reference mock-ups were reasonably consistent. The significance of egg in temperas was characterised by the values of P/S ratio around three (P/S ∼ 3) and the formation of various oxidation products of cholesterol could also be demonstrated at the same time. Additionally, low A/P values (A/P < 0.1) were a characteristic egg identification parameter. On the other hand, the presence of linseed oil in the tempera increased the values of A/P ratios, understandable because azelaic acid is the oxidation product of the oil drying process, while the P/S ratio was lower, due to the fact that the P/S ratio of pure linseed oil is in the range of values 1.0–1.8. Interestingly, the high values of O/S ratio of both drying oils pigmented with verdigris (O/S ∼ 0.5) gave indication of a plausible oleate soap formation, when oleic acid is trapped in the complex with the copper cation of the pigment. 3.2. Paint samples from medieval panels The results of the analyses of the blue paints showed two different methods of use of pigments and techniques on the set of panels investigated. In the first group azurite and lapis lazuli were identified. The results of the micro-Raman spectroscopy in the mapping regime showed the division of the blue layers into azurite and ultramarine. Azurite was usually applied in the under-painting on the

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Fig. 4. TIC chromatogram of blue paint layers from sample 98-88-11, blue reverse side of the cloak, Christ on the Mount of Olives. Note: glycerol (G) and fatty acids from drying oil (Pi: pimelic acid; Su: suberic acid; Az: azelaic acid; My: myristic acid; Pa: palmitic acid; Ol: oleic acid; St: stearic acid); B: diterpenes of soft wood resin (B1: methyl pimarate; B2: methyl isopimarate; B3: methyl dehydroabietate (DHA); B4: methyl-6,7-methoxy-DHA; B5: 7-oxo-DHA; B6: methyl-6,7,15-dimethoxy-DHA; B7: unidentified oxidation product of 7-oxo-DHA); Co: copal components (Co1: methyl copalate; Co2: dimethyl dehydroagathate; Co3: ozic acid, methyl ester).

layer of chalk ground (Fig. 2). Lapis lazuli was used in the top layer of painting. The sporadic grains of lapis lazuli were in the layer of azurite (Fig. 3). In the shadows only lapis lazuli was present, in the light parts of the drapery it was mixed with lead white. This construction of the blue tones was found especially on the paintings ascribed to the main Master – Annunciation, Nativity, Adoration of the Magi and Christ on the Mount of Olives – but also on a work previously considered to have been done by workshop members, Crucifixion. Histochemical staining did not demonstrate the presence of proteins in the blue painting layers. Protein binders showed positive after histochemical staining only on the ground layer (natural chalk). GC/MS analysis possibly identified polymerised walnut oil in the blue layers on the panel Christ on the Mount of Olives and on the Crucifixion panel a plausible mixture of polymerised walnut oil with linseed oil (Fig. 4). As mentioned above, drying oils were generally detected according to the presence of fatty acids and specified by fatty acids ratios. Range of values of P/S ∼ 1.0–1.8 indicated the presence of linseed oil, while P/S ∼ 2.5 revealed walnut oil. The ratio P/S ∼ 2.0 showed the plausible presence of linseed oil, however, an admixture with walnut oil could be also considered. The lower level of azelaic acid suggested the pre-treatment of drying oil. The values of ratios A/P < 05 and A/Su > 5 demonstrated that the oil was pre-polymerised by heat [20]. Resins were identified according to their characteristic markers; soft wood resin was detected according to a series of diterpenes, namely due to the presence of dehydroabietic acid and its oxidation products as 7-oxo-DHA or methyl-6, 7-methoxy DHA. Methyl copalate and ozic acid, methyl

Fig. 5. Cross-section of sample taken from the blue cloud (Descent of the Holy Ghost, 07-48-11): a, b: in reflected light and after histochemical colouring (agent Fuchsin S). The protein containing binders are positive on the chalk ground (1) and organic isolation layer (2). On the two blue layers (lapis lazuli and lead white) are negative (3, 4); c: TIC chromatogram of the ground layer. Note: amino acids from animal glue (Ala: alanine; Gly: glycine; Val: valine; Leu: leucine; Ile: isoleucine; Pro: proline; Ser: serine; Thr: threonine; Phe: phenylalanine; Asp: aspartic acid; Hyp: hydroxyproline). Photo © 2016 The National Gallery in Prague.

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ester possibly showed the presence of African copal, but further investigations would be required to prove this hypothesis [24–27]. The sample from the blue drapery on the Crucifixion panel was taken in the light parts and in the top layer lead white was also present, apart from the lapis lazuli. In the second group, which from the art-historical viewpoint was considered rather to be in the circle of workshop production, exclusively very fine lapis lazuli was identified in the blue paintwork, which was usually backed by a white imprimatura executed in lead. In the shadows only lapis lazuli was present, in the light parts of the drapery it was mixed with lead white. This construction of the layers and the pigments were confirmed on the panels of the paintings Lamentation, Resurrection, Ascension and Descent of the Holy Ghost. The painting of the Resurrection was included from the art-historical viewpoint in the group of the main Master. Identification of the binding materials showed the same distribution of binders as in the first group (Fig. 5). The chromatographic profile of amino acids was depicted on Fig. 5c. High abundance of glycine and the presence of hydroxyproline confirmed animal glue as the major binding medium in the ground layer. In the coloured layers of both groups, however, the presence of protein binding agents was not demonstrated by the GC/MS method; in the paint layers only drying oils, namely polymerised linseed oil and walnut oil,

7

were observed. The use of walnut oil was linked with its greater stability in light (less yellowing) and it was therefore preferred for use in light, green and blue pigments. It also dried more slowly and allowed longer working with the painting. In the painting of the flesh areas the results were similar in nature. The use of pigments in both groups was alike. Differences could be seen, however, in the colour of the under-painting [28–30]. In the first group we defined there was a very dark green-brown under-painting, in which the SEM/EDS and Raman spectroscopy identified earth pigments, in particular green earth and lead white (Fig. 6). The layers of paint were pink, the basis of which consisted of lead white with vermilion, in isolated instances with an admixture of red lead and ochres. In the light tones there was more lead white present in the two pink layers on the under-painting. In the shadows the lower pink layer on the under-painting had a very warm strong reddish shade, as could be seen, for instance, on the stratigraphy of the flesh tone of Christ on the panel Christ on the Mount of Olives. In the second group the under-painting was very light and more of a yellow-green shade, where a mixture of lead white, earth pigments (yellow ochre) and green copper pigment was identified (Fig. 7). On this background, the painting of the flesh tone was again executed in lead white with vermilion. In both cases this was

Fig. 6. Cross-section of sample taken from the flesh of Christ’s hand (Christ on the Mount of Olives, 98-88-3): a, b: in reflected (a) and ultraviolet light (b). On the chalk ground (1) lies green under-painting (2) and two layer of flesh is applied a lead white, vermilion and ochres (3, 4); c: after histochemical colouring (agent Fuchsin S), the protein containing binders are positive on the chalk ground (1) and organic isolation layer (2); d: BSE image of the cross-section. 2D scan mapping of relevant elements – Al, Fe, Hg, Pb. Photo © 2016 The National Gallery in Prague.

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a sophisticated layered technique, where the resulting colour was a combination of several colour layers applied consecutively. Histochemical staining showed the presence of protein binders again only in the chalk ground. GC/MS in both groups showed the main

binding agent to be heat-bodied linseed oil with additions of soft wood resins, or elemi and dammar. The diterpenous resin might be of secondary origin, coming from the later restoration treatments with elemi and dammar resins, or it might have also been added

Table 3 Composition of the samples. Sample

Pigment

98-88-11

Blues Painting: lapis lazuli Under-painting: azurite

Lipid binding medium P/S

05-33-2

Painting: lapis lazuli Under-painting: azurite

06-39-8

Painting: lapis lazuli Under-painting: lapis lazuli, lead white

07-48-11

Painting: lapis lazuli Under-painting: lapis lazuli, lead white

98-88-1

Flesh tones Painting: vermilion, red lead, lead white Under-painting: green earth, yellow and red ochres, lead white, black

05-33-7

Painting: vermilion, lead white Under-painting: green earth, yellow and red ochres, lead white, black

06-39-1

Painting: vermilion, lead white Under-painting: green earth, yellow and red ochres, lead white, chalk, probably azurite

99-39-6

Greens Painting: copper pigment (probably verdigris and malachite), green earth, lead white, yellow ochre

98-88-5

Painting: copper pigment (probably verdigris and malachite), lead-tin yellow type II, lead white Under-painting: copper pigment (probably verdigris and malachite), lead-tin yellow type II, lead white

05-33-4

Painting: copper pigment (probably verdigris and malachite), lead-tin yellow type II, lead white Under-painting: copper pigment (probably verdigris and malachite), lead-tin yellow type II, lead white

06-39-6

Painting: copper pigment (probably verdigris and malachite), lead-tin yellow type II, lead white Under-painting: copper pigment (probably verdigris and malachite), lead-tin yellow type II, lead white

Resins A/P

A/Su

Ch

Pre-polymerised linseed oil/walnut oil

Soft wood resin Traces of African copal

2.0 Heat-bodied linseed oil

0.6

1.4 Heat-bodied linseed oil

0.8

1.8 Pre-polymerised linseed oil/walnut oil

1.0

2.0

0.5

3.7

– Traces of soft wood resin Traces of African copal Traces of dammar

3.2

– Traces of soft wood resin Traces of African copal Traces of dammar

3.0

– Trace of soft wood resin

4.0

–

Heat-bodied linseed oil

Traces of soft wood resin

1.7 Heat-bodied linseed oil

1.5

1.2 Heat-bodied linseed oil

1.4

1.5

1.0

3.9

– Traces of soft wood resin Traces of elemi Traces of dammar

4.0

– Traces of soft wood resin Traces of shellac Traces of dammar

3.4

–

Heat-bodied linseed oil + egg secondary contamination

2.0 Heat-bodied linseed oil

0.8

1.7 Heat-bodied linseed oil

0.9

3.5

Yes Traces of soft wood resin

4.0

– Traces of soft wood resin Traces of African copal Traces of dammar

1.0 1.3 Heat-bodied linseed oil/ + beeswax contamination

1.9

Traces of soft wood resin Traces of African copal Traces of dammar

0.8

3.9

– Traces of soft wood resin Traces of African copal Traces of dammar

3.3

Yes

P: palmitic acid; S: stearic acid; A: azelaic acid; Su: suberic acid; Ch: cholesterol oxidation products.

ˇ u, ˚ et al., A multianalytical study of oil binding media and pigments on Bohemian Panel Paintings Please cite this article in press as: R. Sefc from the first half of the 14th century, Journal of Cultural Heritage (2016), http://dx.doi.org/10.1016/j.culher.2016.10.003

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9

Fig. 7. Cross-section of sample taken from the flesh of St John (Lamentation, 06-39-1): a, b: in reflected and ultraviolet light. On the chalk ground (1) and organic isolation layer (2) lies yellow-green under-painting (3) and pink layer of flesh is applied a lead white, vermilion (4); c: BSE image of the cross-section. 2D scan mapping of relevant elements – Fe, Cu, Hg, Pb. In the under-painting is a mixture of lead white, earth pigments (yellow ochre) and pigment on the base of copper. Photo © 2016 The National Gallery in Prague.

to the oil before its application to accelerate the drying of the oil paint. In the green areas, it was impossible to divide the panels unequivocally into groups on the basis of the layering of the colour layers and the pigments used. A mixture of copper pigment (probably verdigris and malachite), lead-tin yellow type II, ochres and lead white was identified in both groups. What was fundamental, however, was the GC/MS analysis, which showed, only in the green painting, the presence of traces of egg protein binder alongside the linseed oil, proved by the traces of cholesterol oxidation products (cholesta-3,5-dien-7-one and 5-cholestane-3-ol) [31,32], apparently the residues of a later overpainting contamination as histochemical staining had already previously demonstrated the existence of secondary retouching. This would also explain the higher values of P/S ratio observed than would be expected for pure linseed oil. The proteins were indeed identified by GC/MS in the ground layer as animal glue. The list of all chromatographic results was summarised in Table 3. 4. Conclusions The selection of high quality pigments, influenced by the Italian painting techniques of that period, is confirmation of the fact

that the panels were commissioned for the royal court. Our investigation also confirmed the differences in use of pigments in the workshop by individual artists. Regarding binding media, in the framework of the research it appears fundamental to demonstrate purely oil binding medium in the whole set of panels, which are dated to the period before the middle of the 14th century. In this period we are generally speaking of the tempera painting technique, where egg components were used in painting as the main binding medium. In the panel painting of Bohemian provenance the use of an oil binder has so far been demonstrated, alongside the egg tempera technique, on some of the panel paintings attributed to the court painter of Emperor Charles IV, Magister Theodoricus, and his workshop, active in Prague in the sixties of the 14th century [3,33]. The first mention of the use of oil binder was in the manuscript of Theophilus Presbyter De diversis artibus, from the early part of the 12th century, and the use of oil has also been demonstrated in the Norwegian medieval painting [34,35]. The present-day research generally expects the use of oil from the last quarter of the 14th century in the Transalpine region and traditionally the first use of oil in the Transalpine painting is ascribed, with reference to Vasari, to Jan van Eyck [36–38]. The classical tempera technique was still used in Italy in the 15th century. The period practice of the use of binding agents in panel painting, however, took many forms and

ˇ u, ˚ et al., A multianalytical study of oil binding media and pigments on Bohemian Panel Paintings Please cite this article in press as: R. Sefc from the first half of the 14th century, Journal of Cultural Heritage (2016), http://dx.doi.org/10.1016/j.culher.2016.10.003

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the variability of the recipes and the results of research point to many combined techniques, where the binding agent was a mixture based on egg and oil [39]. The blending of tempera and oil painting on a single picture is not exceptional [40]. It is clear that in medieval Bohemia the artists already knew both oil and egg in the first half of the 14th century, due to the influence of North European techniques, and the use of oil in Central Europe is significantly earlier than in Italy. The artists were aware of the different effects of the media that could be achieved. There is a broad agreement, when comparing the criteria of art historians and conservators with our research results, on the material technology, but nevertheless individual differences are evident and, for instance, the Crucifixion panel corresponds more to the panels attributed to the main master. The Lamentation panel, on the other hand, corresponds rather to the stratigraphy and material technology of the panel paintings Ascension and Descent of the Holy Ghost. This unique identification of oil binding media opened up new possibilities for the interpretation of painting techniques in Central Europe in the 14th century. Acknowledgements This work has been financially supported by the project of the Ministry of Culture of the Czech Republic: Historical technologies and modern methods of research. The interpretative possibilities of the specialized methods of research of medieval artworks using innovative technologies (DF 13P010V010). The authors wish to thank Dr Martina Griesser, head of the Conservation Science Department, Kunsthistorisches Museum, for the possibility of using the reference mock-ups prepared in the frame of the research project Chemical Characterisation and Identification of Complex Natural Media Systems in Historic Works of Art by the use of GC/MS and Py-GC/MS, financed by the Austria’s central funding organisation - FWF - Austrian Science Fund (P15640-N03). References ˇ Chlumská, Bohemia and Central Europe 1200–1550. The Permanent [1] J. Fajt, S. Exhibition of the Collection of Old Masters of the National Gallery in Prague at the Convent of St Agnes of Bohemia, The National Gallery in Prague, Prague, 2014, pp. 31–32 (Cat. No. 16, pp. 146–147). [2] J. Peˇsina, The Master of the Hohenfurth Altarpiece and Bohemian Gothic panel painting, Odeon, Prague, 1989, pp. 72–98. [3] J. Fajt, Charles IV. Emperor by the Grace of God. Culture and Art under the last of the Luxembourgs 1347–1437 (Exhibition catalogue), Správa Praˇzského hradu, Prague, 2006, pp. 87–88 (Cat. No. 9). [4] E. Wipfler (Ed.), Kunstechnik und Kunstgeschichte. Das Inkarnat in der Malerei des Mittelalters, Zentralinstitut für Kunstgeschichte, München, 2012. [5] M. Frinta, An investigation of the punched decoration of Medieval Italian and non-Italian panel painting, Art Bull. 47 (1965) 261–265. [6] M. Frinta, Punched Decoration on Late Medieval Painting, Maxdorf, Prague, 1998. ˇ u, ˇ Chlumská, A. Hostaˇsová, An investigation of the lead-tin yellows ˚ S. [7] R. Sefc type I and II and their use in bohemian panel paintings from the gothic period, Herit. Sci. 3 (2015) 16. [8] I. Vernerová, M. Denderová, Unpublished laboratory report, Nos. 98-42, 9888, Archive of Chemical-technological Laboratory, National Gallery in Prague, Prague, 1998. [9] N. Eastaugh, V. Walsh, T. Chaplin, R. Siddall, Pigment Compendium: A Dictionary and Optical Microscopy of Historical Pigments, Butterworth-Heinemann, London, 2008. [10] J.R. Ferraro, K. Nakamoto, C.W. Brown, Introductory Raman Spectroscopy, Academic Press, New York, 2003. [11] C. Coupry, Application of Raman microspectrometry to art objects, Analysis 28 (2000) 39–45. [12] R.J.H. Clark, Pigment identification by spectroscopic means: an arts/science interface, C.R. Chimie 5 (2002) 7–20.

[13] M. Johnson, E. Packard, Methods used for the identification of binding media in Italian paintings of the fifteenth and sixteenth centuries, Stud. Conserv. 16 (1971) 145–164. [14] V. Pitthard, S. Stanek, M. Griesser, T. Muxeneder, Gas chromatography–mass spectrometry of binding media from Early Schönberg’s Palette, Chromatographia 62 (2005) 175–182. [15] V. Pitthard, M. Griesser, S. Stanek, T. Bayerova, Study of complex organic binding media systems on artworks applying GC-MS analysis: selected examples from the Kunsthistorisches Museum, Vienna, Macromol. Symp. 238 (2006) 37–45. [16] R. F. Egerton, Physical Principles of Electron Microscopy, Springer, New York, 2007. [17] M.R. Schilling, Workshop on Binding Media Identification in Art Objects, The Netherlands Institute for Cultural Heritage, Amsterdam, 2003. [18] L. Degrand, Development of a Gas Chromatography Method for the Analysis of Binding Media in the Kunsthistorisches Museum Vienna, 2001, pp. 26–28 (unpublished internal report). [19] M. Doerner, Malmaterial und seine Verwendung im Bilde, Ferdinand Enke Verlag, Stuttgart, 1949. [20] E. Manzano, L.R. Rogriguez-Simón, N. Navas, R. Checa-Moreno, M. RomeroGamez, L.F. Capitan-Vallvey, Study of the GC-MS determination of the palmitic-stearic acid ratio for the characterisation of drying oil in painting: La Encarnación by Alonso Cano as a case study, Talanta 84 (2011) 1148–1154. [21] A. Andreotti, I. Bonaduce, M.P. Colombini, G. Gautier, F. Modugno, E. Ribechini, Combined GC/MS Analytical procedure for the Characterisation of Glycerolipid, Waxy, Resinous, and proteinaceous materials in a unique paint micro-sample, Anal. Chem. 78 (2006) 4490–4500. [22] J.D.J. van den Berg, Analytical Chemical Studies on Traditional Linseed Oil Paints, MOLART Report 6, FOM Institute AMOLF, Amsterdam, 2002. [23] M.P. Colombini, F. Modugno, E. Menicagli, R. Fuoco, A. Giacomelli, GC-MS characterisation of proteinaceous and lipid binders in UV-aged polychrome artefacts, Microchem. J. 67 (2000) 291–300. [24] J.S. Mills, R. White, The Organic Chemistry of Museum Objects, ButterworthsHeinemann, Oxford, 1994. [25] M.P. Colombini, F. Modugno, Organic Mass Spectroscopy in Art and Archaeology, John Wiley & Sons, Ltd, Publication, Chichester, 2009. [26] K.J. van den Berg, Analysis of Diterpenoids Resins and Polymers in Paint Media and Varnishes, MOLART Report 10, FOM Institute AMOLF, Amsterdam, 2003. [27] K.J. van den Berg, J. Ossebaar, H. van Keulen, Analysis of copal resins in 19th century oil paints and resins/oil varnishes, in: R. van Griecken, K. Janssens, L. Van’t dack, G. Meersman (Eds.), in: Art 2002: 7th International Conference on Non-Destructive Testing, Microanalysis for the Diagnostics, Conservation of the Cultural, Environmental Heritage, Antwerp, June 2–6, University of Antwerp, Antwerp, 2002, pp. 1–10. [28] M. Hamsík, On the technique of Czech panel painting of the 14th century. Painted Carnation as development criterion, Technol. Artis 1 (1989) 39–43. [29] E. Wipfler, “Color humanus”. Das Inkarnat in den Quellenschriften des Mittelalters, in: E Wipfler (Ed.), Kunstechnik und Kunstgeschichte, Das Inkarnat in der Malerei des Mittelalters, Zentralinstitut für Kunstgeschichte, München, 2012, pp. 48–65. [30] W.D. Löhr, S. Weppelmann, Fantasie und Handwerk. Cennino Cennini und die Tradition der toskanischen Malerei von Giotto bis Lorenzo Monaco, Ausstellungskatalog Gemäldegalerie Berlin, München, 2008 (10.1.–13.4. 2008). [31] M.P. Colombini, F. Modugno, R. Fuoco, A. Tognazzi, A GC-MS study on the deterioration of lipidic paint binders, Microchem. J. 73 (2002) 175–185. [32] O.F. van den Brink, E.S.B. Ferreira, J. van der Horst, J.J. Boon, A direct temperature-resolved tandem mass spectrometry study of cholesterol oxidation products in light-aged egg tempera paints with examples from works of art, Int. J. Mass Spectrom. 284 (2009) 12–21. [33] M. Hamsík, J. Tomek, Malíˇrská technika Mistra Theodorika, Umˇení XXXII (1984) 377–387. [34] L.E. Plahter, U. Plahter, The technique of a group of Norwegian gothic oil paintings, in: IIC Lisbon Congress, 1972, pp. 131–138. [35] R. White, Analyses of Norwegian medieval paint media. A preliminary report, Norwegian medieval altar frontals and related material: Papers from the Conference in Oslo, 16–19 December 1989, published as Institutum Romanum Norwegiae Acta ad Archaeologiam et Artiam Historiam Pertinentia, XI, 1995, pp. 127–135. [36] P. Coremans, L’agneau mystique au laboratoire, Centre national de recherches ‘Primitifs flamands’, Bruxelles, 1953. [37] G. Vasari, Le Vite de’ piú eccellenti pittori scultori e architettori nelle redazioni del 1550 e 1568. Odeon, 1976. [38] R.E. Straub, Tafel- und Tüchleinmalerei des Mittelalters, in: Reclams Handbuch der künstlerischen Techniken, Bd. 1, Stuttgart, 1984. [39] R. Billinge, L. Campbell, J. Dunkerton, S. Foister, J. Kirby, J. Pilc, A. Roy, M. Spring, R. White, Methods and materials of Northern European painting in the National Gallery, 1400–1550, Natl. Gallery Tech. Bull. 18 (1997) 6–55. [40] M. Hamsík, The importance of paint media in a comparative study of historical technology, Technol. Artis 1 (1989) 20–22.

ˇ u, ˚ et al., A multianalytical study of oil binding media and pigments on Bohemian Panel Paintings Please cite this article in press as: R. Sefc from the first half of the 14th century, Journal of Cultural Heritage (2016), http://dx.doi.org/10.1016/j.culher.2016.10.003