1 Introduction

The National Gallery, Sofia, houses among its collection of art, three paintings on canvas (Figs. 1, 2, 3) inventoried as artworks of unknown artists under the names: “Royalty with a mirror”, 142/77 cm, “Royalty” 142/69 cm and “Royalty with flowers”, 150/68.5 cm that have never been exhibited. Identified as Persian paintings from the Qajar era (1789-1925) by Dr. Iván Szántó [1] in 2016, they actually show a Musician playing Daf (tambourine), Musician playing Santour (hammered dulcimer) and Royalty (Prince) with a basket with flowers.

The first two paintings depict female musicians kneeling onto identical carpets within decorated interiors. The paintings are designed with arched tops. The iconography emphasizes on ornamental details rather than naturalistic portrait features, which is typical for early Qajar art [2]. A flat, two dimension stylization, without focus on true perspective, is featured without halftones. Pearls are meticulously aligned, executed with a stick or flat round tool which builds volume. The third painting represents a full length young man with a crown on his head, thus determining his royal origins, holding a basket with flowers. His richly ornate appearance is recreated, like the Musicians, with great attention to the details and within similar environment.

The interest in large-scale human representations in Persia, going beyond the miniature genre and intended for interior decoration, develops in time. Diplomatic, trading and cultural relationships between Europe and Persia existed during the Ilkhanid, Safavid and Qajar historical periods, leading to influences in the traditional Persian visual arts. Both two- and three-dimensional space interpretations can be seen [3]. At the height of the Isfahan school (Safavid era), there is intention to depict volume, depth, light and shadow. This is the so-called phenomenon “Farangisazi”—a term referring to the introduction of European models and techniques [2]. Early Qajar art is tight to traditions in the beginning with tendency to acquire a more European shape towards the end of the dynasty reign. Principal topics of the early Qajar paintings are the court life, showing enthroned Royalties, together with entourage, hunting or battle scenes [3]. Personal images of lovers, the harem’s life, dancers, musicians and women in European dresses are depicted as well [3]. The royal protocol of the Qajar court, along with the Persian miniature tradition, and the European well-established model of a sitter in front of an open “window” with a background landscape, all together have combined resulting in a compositional plan similar for all the paintings. In the majority of the cases, a subject is placed in between well-balanced vertical and horizontal elements of the interior. The latter can be observed in the paintings from the National Gallery as well. Moreover, the arched tops of the paintings of the Musicians follow a specific shape for each one, designed to fit in particular niches. Like other large-scale Qajar paintings, they were initially created as marouflaged canvas murals for monumental interiors. Some of the Qajar artistic legacy vanished or was reshaped during the Pahlavi period and some surviving examples are displaced and now preserved in different museums and collections [3]. Historically at some point, the Qajar paintings of the National Gallery were converted this way to easel paintings again. Lately, the artworks have been framed in Bulgarian ornamental wooden carved frames from the first quarter of XX century.

In general, the marouflage technique consists in gluing a lighter, flexible material to a stronger, rigid one–in the case of monumental decoration, affixing a previously painted work on canvas to a wall or ceiling substrate [4]. Both the wall and the canvas are coated with an adhesive paste. In this case, the glue should act as an intermediary substance between two materials which differ in properties, possessing high initial tack, bond strength and to provide manipulation time frame. Nailing the edges would hold the mural in place while drying. The marouflage technique was in usage in Europe in the XVII century, with animal glue/starch mixtures being the materials applied [5]. Some disadvantages of aqueous adhesives are the rapid drying time, the occurrence of shrinkage of the fabric and vapour blisters [4, 5]. Variations existed with some additives like Venice turpentine, sugar syrup, honey, linseed oil, alum, etc. [6]. Other traditional recipes included Burgundian pitch, wax, resin and red ochre [5]. In the XIX century in Europe, combinations with lead white (céruse) were used. The reason is improved tack and handling properties, a tendency to dry more slowly and the elimination of the ever-present danger of canvas shrinkage [7]. Paintings marouflaged with lead white paste are extremely durable and often show no signs of cracking [8]. Towards the end of the XIX century, the usage of lead white gradually decreases because of its toxic nature and it is replaced in the XX century with casein and later with vinyl and acrylic adhesives.

On the other hand, the technique of canvas murals is practiced in architectural decoration in Persia during the Ilkhanid, Safavid and Qajar period as well [2]. In some cases, marouflage was applied; in others, only nailing was used. The oldest remaining example of such architectural interior decoration is the mausoleum of Oljayatu in Soltanieyeh, Zanjan province dating back to the XIV century from the Ilkhanid period [2, 9]. The artworks on canvas executed with water soluble paints (animal glue, paste or tragacanth gum binders) were nailed to the walls. Canvas murals and marouflaged murals practice reached its culmination in the Safavid period. The factors that contributed to it were the trading relations with Europe and receiving gifts, art commissions of Armenian traders and the training of Persian painters in Europe who practiced in their homeland [2, 9]. Unfortunately, few examples are preserved (Sheikh Safi-ad-din Ardabili tomb, St. Mary church in Isfahan where some murals were painted in Venice and positioned in place), others have disappeared, living only traces on the walls (Hasht Behesht palace, Ali Qapu in Isfahan). The materials in Safavid times were hemp canvas, oil or aqueous (animal or plant glue) binder medium for the paint layers, and both marouflaged and nailing methods were used for affixing to the substrate. The beginning of oil painting in Persia dates back to the XVII century (Safavid Persia). This practice reached its apogee in the XVIII-XIX century during the reign of Fath-Ali Shah Qajar, consisting in canvas murals installations, with the greatest numbers of such artworks preserved [2, 9]. The early Qajar technique used is oil medium, rarely aqueous (protein or plant) for painting onto hemp and later cotton canvas, almost all marouflaged on the walls with limited colour usage of prevalent warm colours. In the beginning of the Qajar era, some canvas murals were transferred from the old Zand capital–Shiraz from the Vakil palace to the Golestan palace in Teheran [2, 9]. The style of painting in the beginning was similar to the Zand oil painting, as many Zand court painters also worked in the court of Fath Ali Shah. The latter being the first one to patronize the arts, gathered an atelier of painters. Most Qajar royal portraits are signed and dated by court artists such as Mirza Baba, Mehr-Ali, Abdallah Khan, Muhammad Hasan Afshar, Muhammad Isfahani, Mirza Hasan Khan, Khanazad Yusuf and others. Some of the characteristics that differentiate Qajar and Zand paintings are the preferences of certain colours. Green and green harmonizing tonalities are featured in Zand palette. In Qajar era, the dominant colours were different tones of red [10, 11].

The purpose of the present study of the exquisite Qajar art pieces from the National Gallery aims to answer to the following questions:

What are the techniques used? What is the composition of the different layers-canvases, ground layers (fillers and binders), painting layers (pigments, dyes, binders), and protective coatings of the paintings? Do the recognized materials coincide with others from paintings from the Qajar times? Are the recognized materials mentioned in the treatises? To which historical periods do the discovered materials belong and can they be a reference point for dating the works? Can conclusions be drawn about the technological implementation, techniques and possible cultural influences?

And finally, an attempt to make connections with other Qajar works through stylistic and technological characteristics that could provide a guide to authorship/circle.

The selection of study methods is determined by their non-invasive and minimal invasive nature. Non-invasive ones include: X-ray, IR and UV-fluorescence imaging [12]. X-ray imaging is handful for determining structural particularities, the nature of some composition elements like metals and wooden parts, for supplementary information on overpaintings and some heavy metals containing pigments. IR imaging generally gives information for the preparatory drawings and outlines. The UV-fluorescence imaging is useful in recognizing overpaintings and the varnish nature and condition. Micro-samples were taken for analysis and investigation of the protective coatings, varnishes, paint layers, primers, ground layers, adhesives (lining components) and canvases. The wooden frames were studied only stylistically. The micro-samples and cross sections were studied in complementation with optical microscopy (OM), energy dispersive X-ray spectroscopy in a scanning electron microscope (SEM-EDS), attenuated total reflectance Fourier transform infrared (ATR-FTIR), Raman spectroscopy and with non-invasive methods as X-ray, IR and UV-fluorescence imaging. SEM-EDS is chosen for determination of the elemental composition of the ground and paint layers [13], micro-Raman spectroscopy for efficient identification of the mineral pigments and other inorganic components in the complex matrix of the paint [12, 14,15,16] and ATR-FTIR spectroscopy for identification of varnishes, protective layers, organic binders and complementary information on the inorganic components [12, 17,18,19,20].

2 Materials and method

The cross sections were prepared with EPOSIR 7120/46–SIR Industriale SpA. Minimal micro-sample were taken from damaged areas, observed under OM and mounted in the resin. After hardening, the samples were polished with abrasives under control with OM up to high information level.

Micro-extraction was carried out with 0.5–1 mg of each sample, transferred in a glass vial. 50–100 mL of appropriate solvent was added and the vials were sonicated at ambient temperature for 15 min. The liquid part was carefully separated, dropped onto the ATR crystal in order to deposit a film and measure the IR spectrum.

IR and UV-fluorescence imaging was obtained with Fujifilm ls Pro Camera, for IR with R-72 filter, UV-A 395 nm fluorescent black light, AF Micro–NIKKOR 60 mm, f/2,8D lens, Filter B+W Infrared cut filter and B+W Clear UV Haze (010M) MRC.

Polarizing microscope Carl Zeiss Jena, PK 12.5x16m with objectives Planachromat 25x/0.50 and 50x/0.80 is used for the identification on fibres.

Optical microscopy examination was carried out with an Olympus SZX12 microscope, zoom ratio (x9), objective: Olympus DF PLFL 1.6 X PF, Japan. A Canon EOS 550D digital camera was used, with auto extension tubes-DÖRR DANUBIA for CANON EOS, 65 mm (21 mm+31 mm+13 mm), for image acquisition with visible light.

Scanning electron microscopy of the samples was carried out by a JEOL JSM 35 CF instrument upgraded with DIPS, the digital imaging processing system of DISS5, and equipped with energy dispersive X-ray spectroscopy system with SAMx SDD detector (B-U). The accelerating voltage was 20 keV. The elements identified in the samples (in weight %) are provided in the Online Appendix A.

The ATR-FTIR spectra were measured in the interval 4000–600 cm\(^{-1}\), by accumulating 64 scans at resolution of 2 cm\(^{-1}\), on a FTIR Bruker Tensor 27 spectrometer by direct deposition of the micro-samples or extracts on the surface of a diamond crystal ATR accessory.

The Raman spectra were recorded using a LabRAM HR Visible (Horiba Jobin-Yvon) Raman spectrometer in the range 100-4000 cm\(^{-1}\). An objective X50 was used both to focus the incident laser beam onto the sample surface into a spot with a diameter of about 2 \(\mu \)m and to collect the scattered light. The used excitation was He-Ne 633 nm laser line. The laser power on the surface was varied from 0.06 to 6.05 mW.

3 Results and discussion

3.1 Stratigraphy

The thorough observation of the paintings, the samples study under OM and X-ray imaging showed a complex system of layers for both Musicians depictions (Figs. 1 and 2). According to common stylistic and technological characteristics described below, the two paintings appear to originate from the same workshop. The data collected showed the presence of lining canvases for both paintings with numerous additional patches in-between the original textile supports and the lining canvases in multiple areas of tears. The patches outlines are visible under racking light of the rear of the paintings and are detected on the X-rays imaging. The high number of horizontal tears most probably has occurred when both paintings of Musicians were dismounted from the walls. A “strappo” technique might have been used with mechanical stress occurring. The damages most probably have raised a necessity for restoration procedures with relining. The choice of intermediary patching is not a typical restoration practice, which points to local restoration in the country of origin with traditional materials (some of the patches are even pieces of marouflaged paper onto canvas). This local technological restoration approaches can be found during the restoration of other early Qajar paintings examples, where an identical case of patching was observed [21, 22]. The X-ray imaging of the three paintings also gives information about cutting of the canvases edges after stretching onto auxiliary supports–an abrasion mark with sharp metal tool had left imprints onto the wooden frames (Fig. 4 k,l).

Fig. 1
figure 1

Investigated Qajar painting of Musician playing Daf (Unknown artist) with cross sections from different locations: 5d—bluish background; 11d and 11d2—dark hair; 1d and 1b2d—white pearls; 7d, 7d2—blue vest; 9d—ruby stones; 2d, 8d, 8d2, 8d3—golden trousers with floral motives; 4d—red belt scarf (shawl); 3d—orange carpet decoration; 12d—green emerald stones; 3d2—orange from the carpet flowers. Cross sections and microphotography: Yoana Tavitian, painting photography: Ivaylo Levitcharov, National Gallery. Cross sections magnification (100\(\times \))

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The IR imaging of the paintings shows delicate proportions and well-preserved condition of the paint layers under darkened surface due to grime accumulation, materials aging and the presence of overpaintings. The latter are visible in UV fluorescence imaging, appear in areas of damages and horizontal tears, masking cracks (Fig. 4 c,f).

The original layers are as follows: The canvases are covered with light brown ground layers with non-homogeneous, bigger in size particles scattered within them (Figs. 1 and 2) —1d2, 2d, 11d2, 3d, 3c, 6c, 8c, 13c, 15c, etc. The presence of a white layers on the top of the light brown preparations in almost all samples in (Figs. 1 and 2)–5d, 11d2, 1d2, 4d, 1d, 7d, 2d, 3d, and all the cross sections from the Santour player, with exceptions those without stratigraphy, determines the existence of a thin white primer layer for both Musicians paintings underneath the paint layers. OM observation clarifies that the hair of the Musician playing Daf is painted onto the previously applied blue background (Fig. 1)–11d, 11d2. Finally, some varnishes/protections are visible (Figs. 1 and 2)–4d, 5d, 1c, 3c.

Fig. 2
figure 2

Investigated Qajar painting of Musician playing Santour (Unknown artist) with cross sections from different locations: 11c and 12c—green stones (emeralds); 13c—dark hair; 1c—white pearls; 8c—bluish background; 3c, 15c, 15c2, 18c—red upper vest; 19c—red curtain glaze; 10c, 16c—ruby stones; Santour (14c—brown, 2c–floral decoration, 5c—green); 6c—lower blue vest; carpet (4c—brown decoration, 7c—blue flowers, 9c—orange flower); 17c, 17c2—lining adhesive; 21c—protection layer. Cross sections and microphotography: Yoana Tavitian, painting photography: Ivaylo Levitcharov, National Gallery. Cross sections magnification (100\(\times \))

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The painting with the Prince (Fig. 3) is not lined but it consists of three horizontal textile parts joined together which is visible from the X-ray imaging (Fig. 4j). The upper part might be a reinstalled part that suffered tearing. The structure is similar: original canvas, red ground layer with remarkable flexibility (Fig. 3)–14R, 15R; original paint layer (Fig. 3)–9R, 17R; varnish and some local overpaintings (Fig. 3)–1R, 2R visible under OM, in UV fluorescence and X-Ray imaging, most probably dating from the time of previous restoration procedures (Fig. 4 i,j). The painting had suffered multiple damages—having a significant number of horizontal and vertical tears, some patched. The upper and lower constituting canvas parts show signs of separation and previous restoration with overpainted areas (Fig. 4j).

Fig. 3
figure 3

Investigated Qajar painting of Royalty/Prince (Unknown artist) with cross sections from different locations: 6R–red drapery; 15R–dark hair; 9R white pearls; 17R – green stones (emeralds); 18R–ruby stones; 10R–red lower vest; background and architectural representations (1R, 2R, 3R, 7R, 12R, 13R, 14R, 16R); 19R–varnish layer. Cross sections and microphotography: Yoana Tavitian, painting photography: Ivaylo Levitcharov, National Gallery. Cross sections magnification (100\(\times \))

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In the case of the three paintings, areas with metal particles are detected in UV fluorescence. Generally, in metals a UV fluorescence is not induced because they are almost entirely unaffected by UV radiance and appear very dark. In the case of the Prince, Daf and Santour players paintings, this observation appears in all the areas where rubies and emeralds are painted, as well as the golden-greenish coloured trousers of the Daf musician. Both musical instruments also show well-distinguishable parts with metal particles.

When a canvas was mounted as a marouflaged mural additionally to the stratigraphy listed, which does not differ from a traditional easel painting, the whole structure with the mural layers consisted in: support-wall (stone, brick, clay (earth)); lining layer (clay and straw, gypsum, fillers); preparation layer (gypsum, lime, clay, with filler). The gluing paste was applied at this point, for affixing the prepared painting in advance. In some case nails were used to hold the canvas in position [2, 9].

If a mural painting had to be executed on the wall directly without canvas a supporting layer, after the lining layer, was applied with binders and additives as rabbit or fish glue, gum Arabic, grape juice (“shira”), date sap, sugar syrup, gum tragacanth (very common). Earth pigments (common filler for red ground layers used in the Safavid period), calcium carbonate, calcium sulphate, zinc oxide powder (white zinc) and white lead were added [2, 9]. Isolation of linseed oil and sandarac resin or for water soluble colours instead of oil, a mixture of tragacanth gum, plant gum and starch together was used to cover the preparation [10]. The latter technological information demonstrates the materials used for isolation and binding and could be of importance to the study. In the case of calligraphy on paper intended for wall mounting, the paper is glued on the canvas previously, or then gypsum might be used to shape relief decoration for application of gilding [9].

Fig. 4
figure 4

Non-destructive analytical methods. Musician playing Santour: a IR imaging, b visible light, c UV-fluorescence imaging, k X-ray imaging; Musician playing Daf: d IR imaging, e visible light, f UV-fluorescence imaging, l X-ray imaging; g detail, visible light–Protection layer of the pearls 1d (Musician playing Daf); Royalty/Prince: h IR imaging, i UV-fluorescence imaging, j X-ray imaging. Visible light, IR and UV Photography: Ivaylo Levitcharov, National Gallery

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3.2 Materials identification

In order to identify the materials, the samples were subjected to a further investigation by complementary analytical techniques. All samples were characterized first with SEM-EDS in order to determine the elemental composition. The ground layers and the main colours were characterized by ATR-FTIR techniques as simpler and faster way to obtain information on the paint composition directly as a mixture and without sample preparation. Precise identification of the pigments in the highly heterogeneous painting layers was achieved by Raman spectroscopy. As a final step, micro-extraction procedure was carried out on some representative samples in order to separate the organic matter recognized by the IR study and subsequently analysed it again as films deposited on the ATR-FTIR crystal. The studied cross sections and micro-samples along with the identified materials are summarized in Tables 1 and 2. More detailed elemental composition is provided in Table 3 in Online Appendix A.

The painting technique of the three artworks of achieving stylization through flat field elaboration and repetitive colour use allowed the organization of sampling and analysis in groups of primary colour. In the chromatic construction of the paintings of the two Musicians, the yellow colour does not exist as a dominant colour choice, but is rather a composition element in obtaining green colour. For this raison, it is not present as an individual colour layer in Table 1. All the cross sections and samples shown in Figs. 1, 2 and 3 were analysed according to the main building parts of the paintings (grounds, paint layers, protection layers), with consideration of compositional materials, and when identical results were obtained and summarized in Tables 1 and 2 they were commented with illustrative examples.

Table 1 List of analysed samples, from the Musician playing Daf and the Musician playing Santour, identified components, predominant elemental composition and characteristic vibrational frequencies (in cm\(^{-1}\))
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Table 2 List of analysed samples, from the Royalty/Prince, identified components, predominant elemental composition and characteristic vibrational frequencies (in cm\(^{-1}\))
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3.2.1 Musicians playing Daf and Santour

The ground (brown) layer in the portraits of the Musicians was studied on several cross sections from the two paintings (Table 1). In all cases, the SEM-EDS analysis detected Fe, K, Na, Al, Si and O. This elemental composition corresponds to alumino-silicate minerals mixed with Fe-based colouring compounds, such as the natural ochres [23, 24]. The distribution of the Fe in the ground layer is clearly seen in Fig. 5, presenting the elemental mapping on cross section 3d.

Siamak provides some ground recipes used in early Qajar paintings. The fillers and binders listed are: gypsum or white clay with animal glue (fish, rabbit), linseed oil; only gypsum; red earth and lead white with oil; minium and clay (kaolin), quartz, CaCO\(_{3}\) with a gum; gypsum with umbra with oil (with addition of slow drying walnut oil); lead white and CaCO\(_{3}\) with oil. A formula used later in the Qajar art is Barium sulphate with ZnO and ochre [2]. Firouznia, Samanian state fillers gypsum, white lead, minium [25]. Siamak points that some recipes for preparation layers of paintings with quartz powder, kaolin and white lead, together with oils and their compounds are probably imported from Europe [2]. Among a variety of XVI century North and Central European painting preparation layers some include chalk and earthy pigments. There are also XVI century Venetian examples of ground layers made of earthy pigment and blacks, chalk, gypsum, minium and lead white [26].

In the same sample mapping 3d (Fig. 5), it was also observed that Si is concentrated in particular areas, corresponding to the round smoothly shaped particles, visible in the OM pictures of 3c, 6c, 13c, 11c as semi-transparent inclusions (Fig. 5). Summarizing these data, it was concluded that quartz is present, most probably added to the ground layer as filler, accordingly to the listed recipe and because particles do not present sharp edges from grinding. However, a presumption that the quartz normally occurring within the earthy material, was naturally present as very fine fraction but not added, is also possible [27].

Fig. 5
figure 5

Microphotographs of cross sections 3c, 6c, 13c, 11c from the painting of the Musician with Santour with visible quartz particles in the ground layer; optical microscopy, SEM-EDS analysis and elemental mapping of cross section 3d from the orange paint layer. (A—ground layer; B—primer layer; C—paint layer; D—quartz)

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Fig. 6
figure 6

a Micro-Raman spectra of the pigments found in the paint layers of the Musicians–from top to bottom: lead white (Lw) and Prussian blue (P) in the contact zone of white primer and blue paint (7d2-B); red lead (R) in the orange paint layer (3d2); cinnabar (C) and red lead (R) in the red paint layer (15c2); Prussian blue (P) in the blue paint layer (7d2-C); amorphous carbon (B), red lead (R) and cinnabar (C) in the brown-black paint layer (13c); Micro-Raman spectra of the pigments found in the paint layers of the Royalty/Prince: verdigris (V) in the emerald stones (17R-C); forsterite (F) and gypsum (G) in the yellow layer underneath the emeralds stones (17R-B) b ATR-FTIR spectra of paint micro-samples from the Musicians: ground layer (14c), red glazing (18c), blue vest (7d2), green emerald stones (12d), ruby stones (9d); ATR-FTIR spectra of paint micro-samples from the Royalty/Prince: green emerald stones (17R); composite green colour (12R); c ATR-FTIR spectra of varnish and adhesive micro-samples: varnish from the Royalty/Prince (19R), varnish/protection layer from the Musicians (1d), patches glue from the Royalty/Prince (RR2), lining glue from the Musicians (17c2), acetone extract of the lining glue from the Musicians (17c2-ac), hexane extract of the lining glue from the Musicians (17c2-he), cold water extract of the lining glue from the Musicians (17c2-w)

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The white primer layer contains exclusively lead white, as the amount of Pb in the layer is as high as 88.43%, according to the SEM-EDS analysis (Table 1). The white primer layer was characterized by micro-Raman spectroscopy on a micro-sample from the blue vest of the Musician playing Daf (denoted by 7d2 in Fig. 1). The spectrum collected at the contact zone of the white primer layer and the blue paint layer verified the presence of lead white (2PbCO\(_{3}\).Pb(OH)\(_{2}\)) by its characteristic peak at 1053 cm\(^{-1}\) [28]. The Raman spectrum yielded a band at 2154 cm\(^{-1}\) as well. This band was ascribed to the pigment Prussian blue (Fe\(_{4}\)[Fe(CN)\(_{6}\)]\(_{3}\)) [28] whose presence was affirmed in the further analysis as originating from the blue paint layer of the studied micro-sample. The production of Prussian blue is spreading in Europe after 1724 [29] and is available in Persia in the middle of the XVIII century [25].

The white primer layer was characterized also by the ATR-FTIR measurements on several micro-samples where strong IR absorptions at 1390 and 682 cm\(^{-1}\) were observed in accordance with the published spectra of the pigment [30]. Lead white is reported a common ingredient for preparation layers and for colour modulation in the Qajarid oil painting [25].

Sadeq Beyg Afshar (1533–1608) in his treatise “Qanun al-sovar” describes that a painting should have a two-layer ground. The first layer would be gypsum and grape molasses, followed by a second with white lead and oil-varnish. This illustrates the idea of providing isolation characteristics to the layer before the painting is executed and preventing soaking of the binder in the preparation [31]. The XVI century North and Central European preparation layers for canvas paintings often include lead white with or without other pigments additions with an oil binder [26].

The importance of white lead is evident. Siamak cites interviews of prof. Hossein Aghajani, describing the preparation of aqueous colours with physical carrier—a gouache technique where pigments, binders, and white lead are mixed [2]. Other carriers might be Talc, CaCO\(_{3}\) and kaolin.

The SEM-EDS analysis on the orange paint layers in the portraits of the Musicians showed predominant Pb content (Table 1). The Pb distribution illustrated by the elemental mapping on cross section 3d from the floral motives of the carpet of the Musician playing Daf (Fig. 5), form a pattern exactly matching the primer and the paint layer. The micro-Raman measurements on 3d and a second orange micro-sample 3d2 (Fig. 6a) provided peaks at 550, 391, 153 and 122 cm\(^{-1}\) consistent with the characteristic spectrum of red lead (minium) (Pb\(_{3}\)O\(_{4}\)) [28]. Minium Pb\(_{3}\)O\(_{4}\) is an early Qajar period pigment [2].

The SEM-EDS analysis of the red paint layers in the portraits of the Musicians revealed predominant amounts of Hg, Pb, S and Fe (Table 1). An elemental mapping was carried out on cross section 4d from the red belt scarf of the Musician playing Daf (Fig. 7) and clarified that Fe is encountered only in the ground layer, Hg—only within the red paint layer, while Pb is distributed in both the white primer layer and the red paint layer. This elements distribution supported the established composition of the ground and primer layer and made evident that the red paint layer contains Hg and Pb-based pigments. The presence of Hg along with S was further ascribed by the micro-Raman measurements on some darker red grains in micro-sample 15c2 from the red upper vest of the Musician playing Santour to cinnabar (HgS)—based on the peaks at 254 and 344 cm\(^{-1}\) [28], while the lighter red grains in the red paint showed peaks at 122 and 548 cm\(^{-1}\)and were recognized as red lead (Fig. 6a). A mixture of red lead (minium) (Pb\(_{3}\)O\(_{4}\)) and cinnabar (vermillion) (HgS) pigments is reported to be commercially offered and used for economic or artistic reasons [32, 33]. Both early Qajar period pigments are: minium (Pb\(_{3}\)O\(_{4}\)), and cinnabar (HgS) [2].

For identification of the colour applied as dark red glazing over the red upper vest of the Musician playing Santour, a micro-sample (denoted by 18c in Fig. 2) was analysed by ATR-FTIR spectroscopy. The broad absorption around 3200 cm\(^{-1}\), and the bands at 1634 and 1414 cm\(^{-1}\), accompanied by a strong multiplet band centred at 1028 cm\(^{-1}\) (Fig. 6b) were attributed to madder lake dye [34]. Several other bands are visible in the IR spectrum – the most prominent at 2919, 2949 and 1708 cm\(^{-1}\), originating presumably from the varnish layer.

The optical examination of the cross sections prepared from the blue paint revealed light blue layer with darker blue grains scatted within it (Fig. 8). The detected high amount of Fe, as well as Pb, within the blue layer in 7d2, 6c, 7c and 8c (Table 1) suggested that most probably the light blue colour was achieved by mixing Fe-based blue pigment such as Prussian blue (Fe\(_{4}\)[Fe(CN)\(_{6}\)]\(_{3}\)) with lead white (2PbCO\(_{3}\).Pb(OH)\(_{2}\)). On the other hand, in the darker blue grains several elements corresponding to the chemical composition of ultramarine pigment (2Na\(_{2}\)O.Al\(_{2}\)O\(_{3}\).6SiO\(_{2}\).2Na\(_{2}\)S) were detected—Na, S, Al and Si, together with Mg, P, K and Ca. The elemental mapping over the blue paint layer in 7d2 from the blue vest of the Musician playing Daf (Fig. 8) further demonstrated that Fe, Pb, Na, Al and S have relatively uniform distribution over the whole area, while Ca and Si form a similar pattern.

Fig. 7
figure 7

Optical microscopy, SEM-EDS analysis and elemental mapping of cross section 4d from the red paint layer

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The ATR-FTIR spectra of the examined bulk samples from the blue paint showed a band at 2087 cm\(^{-1}\)—for cyano stretching vibration corresponding to Prussian blue pigment (Fe\(_{4}\)[Fe(CN)\(_{6}\)]\(_{3}\)) [30], and bands at 1390 and 682 cm\(^{-1}\)—for lead white pigment (2PbCO\(_{3}\).Pb(OH)\(_{2}\)) (Fig. 6b). Examination of the light blue grains in micro-sample 7d2 by Raman spectroscopy also evidenced the presence of Prussian blue (Fe\(_{4}\)[Fe(CN)\(_{6}\)]\(_{3}\))—identified by its band at 2154 cm\(^{-1}\) [28] (Fig. 6a). The Raman measurements could not yield a spectrum for another blue pigment, but however, taking into account the elements found by the SEM-EDS analysis at the darker blue grains, it was assumed that most probably the second blue pigment is ultramarine (2Na\(_{2}\)O.Al\(_{2}\)O\(_{3}\).6SiO\(_{2}\).2Na\(_{2}\)S). The used ultramarine pigment was most probably of natural origin (lazurite) as the elemental composition indicated admixture of calcite and other minerals, normally absent in the synthetic one [35]. The nearly identical distribution of Ca and Si could be an indication for the presence of the mineral wollastonite (CaSiO\(_{3}\)), reported as a common associated mineral in lazurite deposits [36]. The strong bands between 1200 and 900 cm\(^{-1}\), observed in the IR spectra of the blue paint micro-samples, correspond to Si-O vibrations and corroborate this conclusion (Fig. 4b).

Early Qajar period pigments are: Prussian blue (Fe\(_{4}\)[Fe(CN)\(_{6}\)]\(_{3}\)), lazurite (2Na\(_{2}\)O.Al\(_{2}\)O\(_{3}\).6SiO\(_{2}\).2Na\(_{2}\)S) [2].

Observed in OM the emerald stones of the portraits of the Musicians appear as a transparent green colour layer applied over metal particles or metal leaf (Fig. 2–11c, 12c and Fig. 9b). On the other hand for achieving the golden-greenish aspect of the trousers of the Daf player, the artist has applied metal particles or metal leaf over a glaze like green substance. Because of damages and craquelures, surface dirt and the deteriorated condition of the varnish/protection layer it is difficult to distinguish if small metal particles or metal leaf is applied. From the areas significantly well preserved, a conclusion can be drawn that most probably metal leaf has been used (Fig. 9a). Afterwards, flowers in red and orange colours have been scattered over. When studied with SEM-EDS samples from the Daf Musician trousers (Fig. 1–2d, 8d, 8d2, 8d3), the elements Cu, As, Ag, Au and Zn were detected (Table 1). The incorporation of thin hammered metals (Cu, Au, Ag, alloys of Cu and Sn or Zn), powdered or as leaf, is a common practice in the Qajar art with the purpose of emphasizing on decoration and value [21, 37]. Studies have also confirmed that the use of gold and silver in powdered form or in thin sheets was very common in manuscripts long before the Qajar era [39, 40]. Substitutes of gold like Cu and Sn alloy or Cu and Zn alloy or combination of metals have been used as well [21, 37].

Accordingly, the IR bands at 2829, 2651, 1711, 1585 and 1416 cm\(^{-1}\) found in the ATR-FTIR spectrum of a micro-sample 12d from the green emerald stones (Fig. 6b) matched very well the characteristic bands of copper resinate (Cu(C\(_{19}\)H\(_{29}\)COO)\(_{2}\)) [38]. In the case of the Daf player’s trouser, bright yellow pigment particles are incorporated in the copper resinate (Cu(C\(_{19}\)H\(_{29}\)COO)\(_{2}\)) as well. This is visible in sample 8d—a large yellow particle is present and the SEM-EDS analysis shows As (48.93%), S (34.75%), Si (6.49%), Sb (3.26%), Cu (3.17%), K (1.31%), Fe (1.10%), which indicates the use of orpiment (As\(_{2}\)S\(_{3}\)). The same applies to sample 8d3. Among the early Qajar period pigments, orpiment, silver sheet, golden sheet, powdered gold are described as essential materials [2, 40].

Fig. 8
figure 8

Microphotographs of cross sections 7d, 7c and 5d from the paintings of the Musicians with visible natural ultramarine particles in the paint layer; optical microscopy, SEM-EDS analysis and elemental mapping of micro-sample 7d2 from the blue paint layer

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Fig. 9
figure 9

Details from the Musician with Daf: a Golden-greenish trousers–metal foil particles, red flowers with minium and cinnabar; b Green emeralds with visible metal leaf , laying underneath the copper resinate

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The composition of the brown-black paint layer from the hairs of the Musicians comprises a broad spectrum of elements: Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, Cr, Fe, Co, Cu, Zn, Pb (Table 3 in Online Appendix A). The most prevalent are Ca, Pb, S, Si, P and Fe. Such rich elemental composition suggested the use of black earth pigment. The term “black earth” refers to a wide group of natural earths with varying composition, most generally characterized by the presence of carbonaceous material mixed with clay minerals, in association with calcite, gypsum, quartz, Fe-containing minerals such as pyrite (FeS\(_{2}\)) and jarosite (KFe\(_{3}\)(SO\(_{4}\))\(_{2}\)(OH)\(_{6}\)), or MnO, TiO\(_{2}\), etc. [41]. Considering that P and Ca are present in the layer, it was expected that bone black i.e. amorphous C mixed with hydroxyapatite (basic calcium phosphate (Ca\(_{5}\)(OH)(PO\(_{4}\))\(_{3}\)) and CaSO\(_{4}\), might also be present. The distribution of the elements was clarified by SEM-EDS elemental mapping on micro-sample 13c from the dark hair of the Musician playing Santour (Fig. 10). Fe, Pb and S were found all over the examined area; Si appeared in some distinct areas alone and in some others—associated with Al. The distribution of P correlated mostly to those of Ca. The Raman spectra collected at several dark grains in the brown-black paint layer of micro-sample 13c (Fig. 6a) confirmed the presence of carbonaceous matter (with peaks at 1592 and 1366 cm\(^{-1}\)) [28, 42]. A band at 960 cm\(^{-1}\)for phosphate stretching was not observed in the Raman spectrum, but however, having in mind the earlier reports that the Raman detection of the phosphate band is not always successful [42] and the similar distribution of Ca and P in the paint layer, it was concluded that both black earths and bone black pigment were used in mixture. The Raman spectroscopy detected also the presence of cinnabar (HgS) by the peaks at 255, 283 and 341 cm\(^{-1}\) [28], and red lead (Pb\(_{3}\)O\(_{4}\)) by the peak at 547 cm\(^{-1}\) [28], therefore indicating that the brown colour was achieved by mixing black and red pigments. Some black pigments, without naming, are reported to have been imported from Europe according to Siamak [2].

Fig. 10
figure 10

Optical microscopy, SEM-EDS analysis and elemental mapping of micro-sample 13c from the brown-black paint layer

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The colour of the red ruby stones on the garments of the two Musicians was studied also by ATR-FTIR spectroscopy (Fig. 6b). The ATR-FTIR spectra of micro-samples 9d and 16c exhibited IR bands (Table 1) at 2929, 2858 (C–H stretching vibrations), 1710 (carbonyl stretching vibration), 1640sh (C=C stretching vibration), 1456, 1375 (C–H deformation vibrations), 1242, 1164 and 1037 (C–C and C–O stretching vibrations) most of which might be attributed to shellac vibrations [43, 44] and on the other hand—some of them are close to the IR frequencies reported for lac dye (2929, 2858, 1715, 1623, 1575, 1506, 1453, 1409, 1378, 1309, 1243) [45]. These data suggested that the red material used might be ruby (unbleached) shellac i.e. the raw material obtained from the lac insect containing a mixture of shellac resin and laccaic acid. It is documented that when the entire raw material is used to produce the lac lake pigment this results in the appearance of both the dye and the resin in the pigment [46]. The elemental composition associated with lac lake pigment produced by extraction of the raw material is P, K, Mg, S, with trace of Si, Cl, Al and Cu [46]. According to SEM-EDS analysis of cross section 10c from the ruby stones in the Musician playing Santour, most of these elements are present in the paint. The paint showed also Fe content, which was attributed to earth pigment additives. Nevertheless, for definite identification of the red colourant a more sophisticated analysis by chromatographic methods should be carried out.

Sadeq Beyg Afshar (1533–1608) in his treatise “Qanun al-sovar” describes the preparation and use of Lac Dye. [40].

3.2.2 Royalty/Prince

The composition of the ground layer of the painting of the Prince was observed under OM and studied with SEM-EDS analysis of the cross sections 3R, 12R and 14R (Fig. 3) and (Table 2). In the SEM-EDS analysis, elements Fe, Ca, S, Si, Pb, Al were detected. The fine structure and flexible nature of the ground observed, along with the high content of Fe, Al, and Si points to the use of Armenian bole (Fe\(_{2}\)O\(_{3}\).Al\(_{2}\)O\(_{3}\).SiO\(_{2}\)). Gypsum (CaSO\(_{4}\).2H\(_{2}\)O) was identified as well due to the presence of Ca and S. The visual characteristics in OM and the SEM-EDS results for Pb confirmed define the use of red lead (Pb\(_{3}\)O\(_{4}\)), however addition of some lead white (2PbCO\(_{3}\).Pb(OH)\(_{2}\)) is possible as well. In the XVI century, grounds with content of clay were gaining popularity and started gradually to predominate over chalk and gesso-based grounds. Lately, in the XVII and XVIII century grounds based on clay compounds were highly popular in all European countries [47].

A recipe widely employed by the Venetians is quite similar to the composition established for the Qajar painting of the Prince from the National Gallery, Sofia. The Italian formula consisted of pigments and fillers such as lead white, gypsum, earths and blacks, with the addition of siccatives such as minium or litharge [26].

SEM-EDS analysis of the cross sections collected from the painting of the Prince has shown that the main pigments used to create the colours and tones are similar to those found in the portraits of the Musicians, but in the same time some specific characteristics were also found. The white from the pearls colour is identified in the SEM-EDS analysis of cross section 9R with the presence of Pb being lead white (2PbCO\(_{3}\).Pb(OH)\(_{2}\)). The red colour, represented in the study by cross section 10R collected from red lower vest of the Royalty/Prince, consisted again in cinnabar (HgS) and red lead (Pb\(_{3}\)O\(_{4}\)) mixture as evidenced by the high amount of Hg and Pb detected in the SEM-EDS analysis (Fig. 3) and (Table 2). The blue colour is conferred with Prussian blue (Fe\(_{4}\)[Fe(CN)\(_{6}\)]\(_{3}\)) (Table 2, Fig. 6b)–also a compound along with orpiment (As\(_{2}\)S\(_{3}\)) in the composite green colour of the architectural background (Table 2, Fig. 3 (12R)). The ATR-FTIR spectrum of micro-sample 12R from the composite green colour is depicted in Fig. 6b, where the band of Prussian blue (Fe\(_{4}\)[Fe(CN)\(_{6}\)]\(_{3}\)) pigment is seen at 2087 cm\(^{-1}\).

The emerald stones of the garments displayed two green paint layers (Fig. 11c)—the top one is presumably a later overpainting, because it overlaps existing white pearls in some areas of the cloths like the left arm and the location above the bouquet of roses above the right hand (Fig. 11a and b). Sample and cross section 17R from the emeralds of the Prince painting were studied in detail (Fig. 12, Table 2). The original layer of the emeralds was subjected to SEM-EDS analysis of 17R (Fig. 12b), and it showed Cu and Pb distribution over the whole paint layer (layer C in Fig. 12). The elemental composition found by SEM-EDS analysis on the top green layer, described as the overpainting layer (layer D in Fig. 12) showed a different composition—with predominant content of Cu and As (Table 3 in Online Appendix A). Metal particles (layer E in Fig. 12) are visible under the original green colour with OM and the SEM-EDS analysis points 96.49% metal Cu (Fig. 12, Table 3 in Online Appendix A (17R)). Powdered Au and Ag have been used for centuries in Persian manuscript paintings [39]. In the XVIII and XIX century, imitations of Cu leaf or hammered sheets of Cu alloys with Zn or Sn or both in powder were present in the palette of artists. They could be found widely in Qajar painting art as a mean to emphasize the glittering nature of the emeralds, as previously said [48].

According to the ATR-FTIR spectrum of 17R (Fig. 6b), the upper (overpainting) layer (layer D in Fig. 12) contains emerald green (Cu[C\(_{2}\)H\(_{3}\)O\(_{2}\)]\(_{2}\).3Cu[AsO\(_{2}\)]\(_{2}\)), with IR bands at 1545 and around 1455 cm\(^{-1}\) as a shoulder of the stronger band at 1407 cm\(^{-1}\), which is in use in Europe after 1814 in Europe [9]. It covers thick original layer (layer C in Fig. 12) of verdigris (Cu(OH)\(_{2}\).(CH\(_{3}\)COO)\(_{2}\).5H\(_{2}\)O), with IR bands at 1600, 1430 and 1356 cm\(^{-1}\) [49, 50]. The ATR-FTIR spectrum showed characteristic bands also for lead white-at 1395 cm\(^{-1}\) (as a shoulder) and calcite—at 1405 cm\(^{-1}\), respectively. Verdigris identification was supported by Raman spectroscopy based on the peaks at 2902, 2858, 1594, 1445, 1303 and 525 cm\(^{-1}\)(Fig. 6a) [28]. Additional SEM-EDS elemental mapping analysis of the sample 17R (b) from the green emerald stones in the portrait of Royalty is provided in Online Appendix A.

Fig. 11
figure 11

a–c Macro photography images of the pearls and emeralds of the painting of the Prince with overpaintings; d Cross section 2R of the Prince with overpainting layer; e Cross section 1R of the Prince with overpainting layer; f Detail of the varnish layer of the painting of the Prince

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The yellow colour encountered only underneath the original verdigris layer (Fig. 12) exhibited high amount of Pb, accompanied by minor amounts of Ca, S, Mg and Si. The high amount of Pb indicated the use of massicot pigment (PbO). The micro-Raman measurement at several points of the yellow paint layer of cross section 17R gave strong fluorescence, while gypsum (CaSO\(_{4}\).2H\(_{2}\)O) was identified in some grains—based on the peak at 1010 cm\(^{-1}\) [28]. Along with the gypsum band, another one at 847 cm\(^{-1}\) was observed—it was attributed to the presence of a silicate mineral, most probably forsterite (Mg\(_{2}\)SiO\(_{4}\)) or other mineral of olivine structure [51].

Coarsely ground mica (Mg\(_{3}\)(Si\(_{4}\)O\(_{10}\))) is listed in Persian treatises of being used to provide painting with a glittering appearance. This pigment is mentioned by Seyafi (XVI century), Hossein Aqili Rostamdari (XVI century) and Simi (XVIII century) [40].

The stratigraphy of the sample 2R (Fig. 11d) from the architectural background of the painting of the Prince shows a superposition of a layer of overpainting onto a well-distinguishable layer of varnish. According to SEM-EDS analysis, the composition of the overpainting includes Ba, S, Zn among other elements which witness the use of Lithopone (BaSO\(_{4}\).ZnS). Lithopone is discovered in Europe around 1850 [9]; thus, it can be a guiding point for the overpainting execution. Another sample 1R (Fig. 11e), from the background of the painting near the “window” behind the figure, shows similar stratigraphy under OM, where the same well-distinguishable layer of varnish, assuming original varnish, covers light blue colour layer. According to SEM-EDS analysis Pb, Fe, Al, Si which corresponds to a composition of Prussian blue (Fe\(_{4}\)[Fe(CN)\(_{6}\)]\(_{3}\)) with lead white (2PbCO\(_{3}\).Pb(OH)\(_{2}\)), white clay (Al\(_{2}\)O\(_{3}\).SiO\(_{2}\).2H\(_{2}\)O). This original layer might be recognized as depiction of blue sky. On the top of it there is an overpainting, analysed with SEM-EDS where Pb, As, Si, Ca, Cl, Cu determine Emerald green (Cu[C\(_{2}\)H\(_{3}\)O\(_{2}\)]\(_{2}\).3Cu[AsO\(_{2}\)]\(_{2}\)) with lead white (2PbCO\(_{3}\).Pb(OH)\(_{2}\)) (Fig. 11e). On the microphotograph, some green round-shaped particles with a dark centre are recognized which is typical for Emerald green (Cu[C\(_{2}\)H\(_{3}\)O\(_{2}\)]\(_{2}\).3Cu[AsO\(_{2}\)]\(_{2}\)).

Fig. 12
figure 12

Optical microscopy (a, b), SEM-EDS analysis and elemental mapping of the sample 17R from the green emerald stones in the portrait of Royalty (A—ground layer; B—yellow paint layer; C—green paint layer (original); D—green paint layer (overpainting); E—metal particles)

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3.3 Organic materials identification

The binding medium in the ground layer of the Musicians paintings was identified as animal glue by the presence of characteristic IR bands for proteins at 1638 (amide carbonyl stretching vibration) and 1543 cm\(^{-1}\) (amide N-H deformation vibration) in micro-sample 14c [17] (Fig. 6b). On the other hand, the strong IR bands between 1200 and 900 cm\(^{-1}\) taken into account together with the broader and round-shaped absorption around 3280 cm\(^{-1}\) suggested the presence of a carbohydrate material—those in the region 1200-900 cm\(^{-1}\) might be attributed to C-O and C-C stretching vibrations of the carbohydrates, while the one at 3280 cm\(^{-1}\) corresponds to O-H stretching vibration [17]. A comparison to the IR spectrum of reference glucose showed a very good matching (Fig. 14 in Online Appendix A). Therefore, it can be supposed that the binding medium of the ground layer is a mixture of proteinaceous and carbohydrate material [2, 53].

Siamak provides information about the use of a ground layer in early Qajar art, which recipe’s provenance might come from Europe. It consists in mixing minium and clay (kaolin), quartz, CaCO\(_{3}\) with a gum (plant) binder. Another stated is: gypsum or white clay as filler with binder animal glue (fish, rabbit), linseed oil [2, 25]

Cennino Cennini describes the use of small amounts of starch or sugar in ground layer composition for giving some flexibility [26].

The examined micro-samples from the paint layers of the three paintings showed strong bands at 2920 and 2850 cm\(^{-1}\) (for C-H stretching vibrations) as well as a band in the interval 1710-1740 cm\(^{-1}\) (for carbonyl stretching vibrations) (Table 1, 2). In the micro-samples from the Musicians paintings (Fig. 6b), the latter band was asymmetrically shaped with shoulders at 1730 and 1711 cm\(^{-1}\). These spectral features were attributed to the presence of an oil binder (with carbonyl band at1730 cm\(^{-1}\)), partially hydrolysed (i.e. fatty acids with carbonyl band at 1711 cm\(^{-1}\)) due to the interaction of the triglycerides with metal ions from the pigments [54]. Early Qajar period binders for colours are: linseed oil, polymerized linseed oil, linseed oil with a combination of a mixture of pine resin with walnut oil, wax. The common binders for murals and manuscripts, preceding the use of oils, were animal glue, gums, resins, egg yolk [2].

The varnish layers of the three Qajar paintings were studied by UV light and ATR-FTIR spectroscopy (Table 1, 2). The UV-fluorescence imaging shows an orange reaction to the applied UV radiance, more distinctive in the painting of the Prince, due to a irregular varnish with thickness up to 0,5-1,0 mm, which confirms the presence of shellac (Figs. 4i, 11f) [37, 55]. The ATR-FTIR spectroscopy on micro-sample 10R and 19R also revealed the characteristic bands of shellac—3275, 2923, 2851, 1707, 1166, 1095, 1051, 983 and 719 cm\(^{-1}\) [43, 44] for the varnish collected from the painting of the Prince (Fig. 6c). Two more bands were observed at 1517 and 1460 cm\(^{-1}\) indicating carboxylate transformation products.

Additionally, in the portraits of the two Musicians, a protective coating layer can be observed on the top of the varnish most probably in relation with the historical restoration (Fig. 4g). Both layers are very thin and could not be separated from each other, a micro-sample collected from the upper layer by gentle wetting of the surface was subjected to the IR analysis. During this procedure, it was observed that the protection layer is soluble only in cold water, pointing out to a gum medium rather than animal glue, as the latter reacts to hot water. The IR spectra of micro-samples 1d, 11c and 21c (Fig. 6c) displayed bands at 2929, 2858 (C–H stretching vibrations) and 1707 cm\(^{-1}\) (carbonyl stretching vibration) corresponding to a plant resin and in the same time—bands characteristic for carbohydrates such as the strong and round-shaped absorption in the region 3650-3000 cm\(^{-1}\), and the bands between 1200 and 850 cm\(^{-1}\). The spectrum showed also a strong band at 1640 cm\(^{-1}\). According to the historical documents and earlier studies on Qajar paintings, the most frequently used media for protection layers are animal (fish) glue, fruit (grape or fig) juice or sugar syrup, gum tragacanth or linseed oil mixed with sandarac varnish [2]. For isolation in the mural technique, when painting with water soluble colours is intended, instead of oil compound, a mixture of tragacanth gum, plant gum and starch together was used to cover the plaster [10].

Further, micro-extraction of 19R and 21c with isopropanol was carried out and provided a good coincidence with the spectrum of a reference shellac resin (Fig. 15 in Online Appendix A). Considering the observed spectral bands, the examination with UV irradiation and solubility during the micro-sampling, it was concluded that the varnish layer is composed of shellac in the case of the three paintings, while an additional protection layer in the case of the two Musicians is applied later on. On the other hand, the presence of carbohydrate bands in the spectra of micro-samples 1d, 11c and 21c point out that the protection layer consists of carbohydrate material, very probably gum tragacanth mixed with sugar.

The patches adhesive in the painting of the Prince showed an ATR-FTIR spectrum for proteins i.e. animal glue, illustrated by micro-sample RR2 in Fig. 6c. The lining glue in the portraits of the two Musicians showed more complex composition—in the ATR-FTIR spectrum of micro-sample 17c2 the characteristic bands for proteins were observed along with a shoulder band for triglycerides at app. 1730 cm\(^{-1}\) and more intense absorption in the region 1200-900 cm\(^{-1}\) (Fig. 6c). Micro-extraction with acetone, hexane and cold water supported the identification of triglycerides (oil) in the acetone extract (17c2-ac), free fatty acids in the hexane extract (17c2-he) and carbohydrate in the cold water (17c2-w) [56].

Fibres from the original canvases of the three paintings and the lining canvases of the Musicians were studied with cross-polarized light microscopy (Fig. 13). The samples from the original canvases of the Musicians were identified both as hemp due to the presence of dislocations (nodes), irregularities and tapered ends (Fig. 13 a, c) [58]. Both lining canvases of the Musicians and the original canvas of the Prince showed distinctive features for cotton being naturally “ribbon” twisted, which is due to the natural drying of the fibre [57]. Hemp canvas supports are reported to have been used in painting for marouflaged and canvas murals in Ilkhanid, Safavid and Qajar historical periods. [9]

Gradually, fine cotton (calico) canvases are gaining popularity, slowly replacing the use of thicker, rough canvases like hemp. Many Qajar canvas paintings are created onto cotton support [25].

Fig. 13
figure 13

Cross-polarized light microscopy of fibres from the canvases: a Musician with Daf–original; b Musician with Daf–lining; c Musician with Santour–original; d Musician with Santour–lining; e Prince/Royalty–original; Magnification 10\(\times \)

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In summary, the non-destructive investigation methods, the samples and cross sections studies with the analytical methods applied contributed to identify the complex system of stratigraphy, identical for the two paintings with Musicians playing Santour and Daf. The original canvases identified by OM for both paintings are made of hemp and the lining ones from cotton. The combined data from SEM-EDS, ATR-FTIR and micro-Raman spectroscopy showed that the materials in the composition of the paintings ground layers are alumino-silicate minerals mixed with Fe-based colouring compounds—natural ochres, gypsum, white lead and red lead. The paint layers are created using white lead, red lead, cinnabar, madder lake, lac dye, bone black, black earths, Prussian blue, natural ultramarine, copper resinate, orpiment, silver and gold imitations (copper alloys with Zn and Au) in leafs or powdered. The ATR-FTIR spectroscopy analysis suggested that oil (triglycerides) is the medium (binder) for paint layers and a component of the lining glue formula. Collagen glues (proteins) play the role of binders in the ground layers and the lining adhesives. According to the IR analysis, the varnish coatings are shellac resin and additional protective coatings of carbohydrates were applied, most probably after fixing tears and lining.

The third painting—Royalty/Prince under study is painted on a cotton canvas and it is composed of Armenian bole, gypsum, red lead and possibly white lead for the ground layer. Pigments used for the paint layer are lead white, white clay, bone black, black earths, red lead, cinnabar, Prussian blue, verdigris, green earth, copper resinate, orpiment, metal copper, Emerald green (overpainting) and Lithopone (overpainting). Shellac is the resin applied for the varnish layer. Oil (triglycerides) is the binder agent for colours, and animal glue (proteins) is found in the ground layer. The latter is used as adhesive for patching in areas with tears and small damages.

The paintings demonstrate the usage of few new materials brought to Persia in the XVIII and XIX century like umber, possibly black earth, Prussian blue, Emerald green and Lithopone that may have been imported from Europe [2].

The materials found in the composition of the three paintings from the National Gallery, Sofia, except those imported to Persia, coincide with the traditional listed in the treatises [40, 52, 53]. Additionally, the stylistic features and iconography of the Musicians paintings, as well as the identical depicted carpets with repetitive floral motives in the style “Mina-Khani” [59] relate the two paintings from the National Gallery, Sofia to other early Qajar paintings from the beginning of the XIX century, made by court painters [3].

4 Conclusions

The detailed study and analysis of the three Qajar paintings, representing Musician playing Daf, Musician playing Santour and Royalty/Prince from the collection of the National Gallery, Sofia, presents in-depth information on the techniques and composition materials of the paintings by keeping at the same time, close communication with related Art history and technology.

The identified materials and processes of the three Qajar Paintings from the National Gallery, Sofia witness the close relation with traditions in Art from earlier Safavid and Zand periods. At the same time, the use of a few new European materials and techniques is an evidence for multicultural relation and exchange. The colour systems applied, along with the iconography, even the choice and restoration procedures undertaken, all of that proves continuity. According to the stylistic and composition features, the paintings can be classified as belonging to the Period of Fath-Ali Shah (1797-1834). Moreover, the use of hemp canvas as support for the Musicians paintings can narrow this timeframe and situate the production of the art pieces even in the very beginning of the Qajar era. A possible provenance of the two Musician players paintings could be the Royal court workshop. The painting of the Prince is a valuable meticulously created portrait of a renowned person. Thus, sharing information about their existence, materials and technology is a contribution to the history of art of the Qajar period in general.

Materials knowledge and condition evaluation is a very important necessary step prior conservation and restoration planning. The study of the composition of the paintings will determine the direction of the conservation and restoration approaches to be applied.

The micro-Raman spectroscopy due to its high special resolution and broader spectral range gave advantage in the pigments analysis, while the ATR-FTIR spectroscopy could provide fast information on the composition of the bulk micro-samples including organic matter and fluorescent materials such as silicates whose identification was hampered by Raman measurements. For definite identification of the organic material composition however, a more sophisticated analysis by chromatography methods should be carried out.