MS) to characterize the lacquer objects from Xiongnu burial complex (Noin-Ula, Mongolia)

Microchemical Journal 130 (2017) 336–344

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Microchemical Journal journal homepage: www.elsevier.com/locate/microc

Multi-analytical approach (SEM-EDS, FTIR, Py-GC/MS) to characterize the lacquer objects from Xiongnu burial complex (Noin-Ula, Mongolia) Elena Karpova a,b,⁎, Andrey Nefedov a,b, Victor Mamatyuk a,b, Natalia Polosmak c, Lyudmila Kundo c a b c

N.N. Vorozhtsov Novosibirsk Institute Of Organic Chemistry SB RAS, Lavrentiev ave. 9, 630090 Novosibirsk, Russia Novosibirsk State University, Pirogov street 2, 630090 Novosibirsk, Russia Institute of archaeology and ethnography SB RAS, Lavrentiev ave. 17, 630090 Novosibirsk, Russia

a r t i c l e

i n f o

Article history: Received 5 September 2016 Received in revised form 12 October 2016 Accepted 12 October 2016 Available online 13 October 2016 Keywords: Noin-Ula Oriental lacquer Urushiol Drying oil Colophony

a b s t r a c t A multi-analytical investigation was carried out to study lacquer objects from Noin-Ula burial complex (Mongolia, the first century AD). This complex is a unique source of information about Xiongnu - one of the most ancient nomadic empires, due to the variety of findings of different origin. This study was undertaken to characterize the materials used for manufacturing and decoration of lacquer everyday life objects and works of art from the 22nd and 31st Noin-Ula barrows. Scanning electron microscopy coupled with X-ray microanalysis (SEM-EDS), FT-IR spectroscopy and pyrolysis coupled with gas chromatography/mass spectrometry (Py-GS/MS) and derivatisation in situ with tetramethylammonium hydroxide were used to study both organic and inorganic components of ancient lacquer wares. The components of the drying oil and urushiol were identified in the lacquer coating compositions. Diterpenoid resin and polycyclic aromatic hydrocarbons (charcoal components) were found in some samples. Inorganic pigments of the lacquer wares were umber, iron oxides, cinnabar, orpiment and charcoal. © 2016 Elsevier B.V. All rights reserved.

1. Introduction Lacquer is one of the most important inventions of ancient China together with the invention of gunpowder, paper and porcelain. Lacquer production originated in the Neolithic era and became an independent handicraft industry in the Warring States period (481–221 BCE). The period of Western and Eastern Han is considered the apogee of Chinese lacquer art [1]. Lacquer was used for coating shields and armor, scabbards for swords and quivers for arrows, pikestaffs and parts of chariots, musical instruments, clay figurines, coffins, furniture, boxes and caskets [2]. Quite a lot of the lacquer wares of the Warring States period were preserved. In that time the manufacture of the household utensils increased over the producing of ceremonial objects. The cups of a characteristic ellipsoid form were the most widespread during the Western Han [3,4,5]. These cups were among the gifts of the Han court to Xiongnu Chanyus and often present in Xiongnu graves on the territory of Mongolia and Transbaikalia. Hieroglyphic inscriptions on the lacquer cups and other vessels from Noin-Ula burials gave the opportunity to find out the date of the creation of the barrows, and the place and time of lacquer wares production [4,6,7]. No less interesting other lacquer items which were found in the graves of the Xiongnu. ⁎ Corresponding author at: N.N. Vorozhtsov Novosibirsk Institute of Organic Chemistry SB RAS, Lavrentiev ave. 9, 630090 Novosibirsk, Russia. E-mail address: [email protected] (E. Karpova).

http://dx.doi.org/10.1016/j.microc.2016.10.013 0026-265X/© 2016 Elsevier B.V. All rights reserved.

In ancient China the sap of the lacquer trees [8,9,10,11,12] and tung oil [13,14] were used to obtain the lacquer coatings. A large number of East Asian lacquer wares were colored in red with cinnabar. Cinnabar poorly mixed with lacquer trees sap (urushiol et al.); therefore it was pre-rubbed with tung oil [5]. The optimum oil content in the lacquer allowed obtaining the best strength and protective properties of the lacquer coatings. The excess of oil in the composition lowered its price, but led to deterioration in the properties of the coating. The optical properties and mechanical characteristics of the lacquer coatings were also depended on the nature of the modifiers (resins) added to the lacquers [15]. All resins which were used in the preparation of lacquers, usually divided into hard (the softening temperature 100–120 °C) and soft (the softening temperature 55–95 °C). The hard resins (copal) give with oil solid, durable, flexible enough and shining but dark coatings. The soft resins (diterpene colophony and sandarac and triterpene mastic and dammar) allow obtaining light, but less resistant and less stable lacquer coatings [16]. This study presents the results of combined analyses of the lacquer objects from the dated archaeological Xiongnu burials located outside of China. The aim of the work was to determine the nature of lacquer and pigments which have been used for the manufacture of the unique ancient lacquer wares. The characterization was carried out by scanning electron microscopy with X-ray microanalysis (SEM-EDX), Fourier transform infrared spectroscopy (FTIR) and pyrolysis coupled with gas chromatography/mass spectrometry (Py–GC/MS).

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FTIR gives primary information on the composition of the studied sample. Together with SEM FTIR-ATR allows assessing the degradation degree of the objects surfaces. SEM coupled with EDX provides data on the mineral composition and hence on the filler and the decoration of the archaeological objects. Analytical pyrolysis coupled with gas chromatography/mass spectrometry is a powerful tool for analysis of the organic matrix, typically polymer, such as proteins, polysaccharides, plant gums, polymerized natural resins and drying oils [17–19]. 2. Materials and methods 2.1. Archaeological samples Nine samples of lacquer wares from the 22nd and two samples from the 31st Noin-Ula barrows were analyzed. Five samples are the fragments of a chariot, other lacquer wares are from the burial chamber. The samples from the 31st barrow are two lacquer cups. The list of the samples is shown in Table 1. All objects of the study were in the different degrees of preservation. The chariot was found in the 22nd barrow to a depth from nine meter (umbrella) to ten meters (wheels) and was preserved worse then the objects in the burial chamber to a depth of 16 m. The umbrella of the chariot is almost destroyed (Fig. 1a). The umbrella covering, probably of silk, has completely disappeared. Only a trace of the bordure on the edge has remained because of its covering with the layer of pigment. The spokes, which were made of wood, have preserved only close to the metal tips. Only lacquer coating of the rest length of the spokes has remained. The walls of the chariot body are better preserved (Fig. 1b). The outer surfaces of the walls were coated with lacquer colored with red pigment, the inner surfaces were primed, but were not colored and remained black. The burial chamber of the 22nd barrow was at a depth of 16 m. The lacquer objects in it were destroyed during the robbery of the barrow in the ancient times and have been preserved in a form of fragments. The burial chamber of the 31st barrow was at a depth of 13 m. The lacquer cups found in this barrow were squashed but remained in one piece. Fig. 2 shows the lacquer wares or their fragments from the burial chambers of the both barrows. 2.2. Methods Analysis of the samples was performed by Scanning electron microscopy (SEM-EDS), FTIR spectroscopy and pyrolysis gas chromatography/ mass spectrometry (Py-GC/MS) with derivatisation in situ with tetramethylammonium hydroxide (TMAH).

Table 1 Description of the analyzed samples. Sample number

Object

Description

4-22

Coating of the umbrella spokes of the chariot Bordure on the edge of the umbrella of the chariot Coating of the side wall of the chariot body Coating of the front wall of the chariot body Coating of the chariot wheel spoke Net of a headdress Fragment of a lacquer ornamental object Umbrella spoke Worktop of a lacquer table Lacquer eared cup Small lacquer cup

Brown lacquer

5-22 7-22 8-22 12-22 29-22 77-22 78-22 22-22 27-31 44-31

Red substance on the clay Red lacquer on a black primer Brown lacquer Red lacquer Dark brown lacquer Brown lacquer Brown lacquer Brown lacquer Brown lacquer Brown lacquer

Fig. 1. Fragments of the chariot during the excavation: umbrella (a), walls (b).

SEM-EDS was used to study the condition of the lacquer coatings and elemental analysis of the pigments (fillers). FTIR method gives an indication of the nature of the lacquer, degradation degree and contaminations. Pyrolysis gas chromatography/mass spectrometry is the most informative method to characterize the organic substances of the lacquer wares. 2.2.1. FTIR FTIR data was obtained using a spectrometer Tensor 27 (Bruker, Germany). The transmittance spectra (4000–400 cm−1) were collected as KBr pellets at a resolution of 4 cm−1 with 32 scans. A PIKE MIRacle™ ATR accessory equipped with a single reflection Zinc Selenide crystal was used for surface analysis at a resolution of 4 cm−1 with 64 scans in the range of 4000–630 cm−1. 2.2.2. SEM-EDS SEM-EDS measurements were carried out with a TM-1000 scanning electron microscope (Hitachi, Tokyo, Japan) equipped with an energy dispersive X-ray spectrometer (EDS, SwiftED, Oxford, UK). The SEM was operated at an accelerating voltage of 15 keV in a charge-up reduction mode. 2.2.3. Py-GC/MS Analytical pyrolysis with tetramethylammonium hydroxide (TMAH, 25 wt.% solution in methanol, Sigma–Aldrich Inc., USA) as methylation agent for the in situ derivatization of pyrolysis products was applied. The instrumentation consisted of a Pyroprobe 1500 Series pyrolyzer connected to a gas chromatograph 7890 A (Agilent Technologies, USA) equipped with an HP-5MS fused silica capillary column (stationary

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E. Karpova et al. / Microchemical Journal 130 (2017) 336–344

Fig. 2. Lacquer wares from the burial chamber of the 22nd barrow: fragments of a worktop of a lacquer table (a), a net of a headdress (b), a fragment of a lacquer ornamental object (c) and a fragment of an umbrella spoke (d); the 31st barrow: a lacquer cup (e), a small lacquer cup (f).

phase 5% diphenyl – 95% dimethyl-polysiloxane, 30 m × 0.25 mm i.d., Agilent Technologies, USA). The GC was coupled with a 7200 Q-TOF mass selective detector (Agilent Technologies, USA) high-resolution time of flight mass spectrometer operating in electron ionization mode (EI) at 70 eV. The pyrolysis temperature was 600 °C, which was maintained for 20 s using a platinum coil probe and quartz sample tubes. Samples (100 μg) and TMAH (5 μL) were inserted into the centre of the pyrolysis quartz tube with quartz wool, and then placed in the pyrolysis coil filament. The interface temperature was 180 °C. The GC–MS injector was used in split mode, at 300 °C and 1:100 split ratio. Chromatographic oven conditions were as follows: initial temperature 50 °C, 12 min isothermal, 10 °C min− 1–280 °C, 2 min isothermal, 15 °C min−1–300 °C, 10 min isothermal, carrier gas: He (purity 99.995%), constant flow 1.0 mL·min−1. Peak assignments were performed using mass spectral libraries (NIST 11.0) and with published mass spectra. Formulas of substances were determined according accurate masses of molecular ions. 3. Results and discussion 3.1. Infrared spectroscopy FTIR spectra of the lacquer coatings of the chariot in absorption mode are shown in Fig. 3a. As can be seen from the spectra the samples mainly consist of silicates. Their absorption bands are 1034, 801, 783, 531, 470 cm−1. The bands at 1597, 1414 cm−1 correspond to the vibrations of carboxylates of calcium soaps. The band 1597 cm−1 is superimposed on the vibrations of the adsorbed water and therefore in some samples it appears as a shoulder peak on the background of

1630 cm−1. The spectra of all samples, except for 5-22, have the band at 1708 cm−1, which characterizes the absorption of carbonyl groups. The absorption bands at 2928, 2856 cm−1 correspond to the vibrations of methylene groups. The ratio of the intensities of absorption of methylene groups and silicates characterizes organic matter content in the lacquer. As can be seen from the spectra the least amount of organic substances is in the bordure of the chariot umbrella. This may be due to manufacturing technology of the umbrella or the destruction of organic material in the burial. ATR spectra of the samples 4-22, 7-22, 8-22 and 12-22 show the absorption bands at 1540 and 1456 cm−1 which coincide with the absorption of calcium stearate (Fig. 3b). That is the saturated acids such as stearic and palmitic remain in the lacquer coatings after oil drying and interact with metal cations (mainly calcium) from groundwater, transforming into the corresponding salts. FTIR spectra of the lacquer wares from the burial chambers are shown in Fig. 4. The spectra of the samples 22-22, 29-22, 78-22, 27-31 and 44-31 are similar to the spectra of the lacquer coatings of the chariot and they are the absorbance of silicates and organic binder. Lacquer of the sample 22-22 is best preserved of all analyzed lacquer wares. The absorption bands due to vibrations of methylene groups at 2926 and 2854 cm−1 (stretching vibrations), 1470 cm−1 (scissoring vibrations) and 725 cm−1 (long chain alkanes) have a greater intensity in the spectrum. The band at 1713 cm−1 which characterizes carbonyl group and the broad band at 2766–2390 cm−1 indicate the presence of the free carboxyl groups in lacquer. These absorption bands also present in the spectra of the samples 29-22, 78-22 and 27-31, but their intensities are lower. The spectra of all five samples have the absorption bands of carboxylates and silicates. Moreover, the silicate absorption bands

Fig. 3. FTIR spectra of the lacquer coatings of the chariot: (a) absorbance mode, (b) ATR spectra in the region of 1850–1250 cm−1.

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Fig. 4. FTIR spectra of the lacquer wares from the burial chambers.

dominate in the spectrum of the sample 44-31. Analysis of the IR-spectrum of the sample 77-22 showed that lacquer in it coated the bone. The absorption bands 1653, 1453, 1034, 604, 564 cm−1 belong to hydroxyapatite which characterizes bone wares [20]. These bands dominate in the spectrum. 3.2. Scanning electron microscopy The surfaces of the lacquer wares and the compositions of the inorganic substances in them were analyzed by scanning electron microscopy with X-ray microanalysis. All lacquered surfaces of the chariot were in the different degrees of preservation. Among fragments of the chariot the lacquer coating of the umbrella spokes was best preserved. Flakes of its lacquer were smooth and glossy. The spokes were made of wood; a thin layer of wood remained on the back side of the lacquer flakes. The trace of the bordure on the edge of the chariot umbrella today is a pigment that once coated the fabric of the umbrella. The weave structure still can be seen (Fig. 5). The lacquer coating of the chariot side wall has a matt red surface with a black base which is viewed under the red pigment. Lacquer partially destroyed; its surface has a porous structure. The lacquer coating of the front wall was preserved much worse, it is practically disappeared, and the sample is a soil layer with remaining particles of a pigment on it. Lacquer of the spokes of the wheels looks like the coating of the chariot side wall - a black lacquer base covered with a red pigment, but its preservation is worse. Table 2 shows the composition of the surface of the lacquer wares and clay from the burial, which permeated all items in it. According

the analysis the clay is the composition of aluminum, magnesium and potassium silicates, with iron, titanium, and calcium compounds (oxides). The main element in lacquer of the sample 4-22 is calcium. In small amounts it is a part of the clay polluting lacquer surface. But the main content of calcium falls on calcium soaps that are formed during the interaction of lacquer and calcium salts of groundwater entering the burial. This process is similar to the formation of zinc and lead soaps in the process of aging of oil paints on old paintings [21]. Brown color is probably the color of lacquer, as the iron content in this sample is low. Its surface is contaminated with copper compounds, probably because of the bronze tips. The orange-red pigment of the trace of the bordure on the edge of the chariot umbrella is red ocher. The dark brown color of the sample 8-22 is due to the earth pigments, probably umber, i.e. iron and manganese oxides. The red coatings of the samples 7-22 and 12-22 are mercury (II) sulfide - cinnabar. The black pigment of the base is probably charcoal. The sample 29-22 (lacquer net) is a net of silk (yarn thickness of 8 μm) which is coated with lacquer (Fig. 6). The lacquer is well preserved and has a smooth glossy surface. A mineral base of this lacquer is silicates with iron oxide. The lacquer surface was coated with lead compounds, however, due to the interaction with sulfur compounds from the burial they became of black color. Lacquer of the object with an ornament (77-22) is well preserved. The brown surface of the fragment without an ornament is colored with cinnabar and has quite a lot of iron oxides in it. The patterned

Fig. 5. Micrograph of the bordure on the edge of the chariot umbrella under different magnifications (a ×150 and b ×1000).

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Table 2 The composition and characteristics of the pigments of the lacquer wares. Sample

Elemental composition (%) Mg

4-22 5-22 red 7-22 red 7-22 black 8-22 12-22 red 12-22 black 22-22 29-22 77-22 base 77-22 ornament1 77-22 ornament 2 78-88 27-31 red 27-31 brown 44-31 brown Clay from the burial

+ + +

+ +

+

Al

Si

4 + 36 13 8 2 11 5 6 9 3 3 12 9 11 23 16

14 4 7 30 32 5 23 12 11 22 9 6 20 3 6 13 37

P

+ 3

2

Pigment S

6

13 4 10 13 12 31 16 16 16 16 5

K + 38 6 10 6

4 + 3

1 7

Ca

Ti

Mn

71 +

Fe

Cu

4 89

7 3

Hg

Pb

Sn

4

+

As

3 10 4

+ 2

3 16 8 4 4 15 2 11 18 8

6 3

fragment is colored with cinnabar and arsenic sulfide (orpiment); the content of cinnabar is very high in the lines of the pattern. This suggests that the upper part of this ware was covered with a layer of cinnabar and then with a layer of orpiment. The pattern lines were scratched in the orpiment layer till cinnabar. The bottom of the ware was reddishbrown, the top - yellow with red stripes pattern. Unlike other lacquer wares coated with cinnabar this object does not have a bright red color. Its darkening was happened probably by a similar mechanism with the darkening of colors in historical paintings [22,23]. Iron oxides were used as a pigment of the spokes of the umbrella (78-22) and the basic background of lacquer cups. Red patterns on the cup 27-31 were made of cinnabar. 3.3. Pyrolysis gas chromatography–mass spectrometry All samples showed approximately the same composition of the main organic substances. Table 3 shows the list of identified compounds of the pyrograms of the lacquer wares after TMAH methylation. The compositions of almost of all analyzed lacquer wares consist of four components - urushiol, drying oil, polycyclic aromatic hydrocarbon (charcoal components) and resin. 3.3.1. Fragments of urushiol The fragments of urushiol – alkylcatechols – were clearly identified in all samples except 5-22 and 29-22. Fig. 7a shows extracted ion chromatogram of the ion with m/z 136 of the sample 77-22 which has the richest composition of alkylcatechols (Table 4). Ion with m/z 136 corresponds to dimethoxyphenyl moiety which is formed after losing of the alkyl chain.

7 4

29 38 12 27 57 14 19 11 8 30 4 33 33 26

67 24 48 2

27 28 59

18 3

2 3 1

65 20

– Ocher Cinnabar Umber Umber Cinnabar Iron oxides Iron oxides Lead compounds Cinnabar, iron oxides Orpiment Cinnabar Iron oxides Cinnabar Iron oxides, an impurity of cinnabar Iron oxides

Alkylcatechols and alkylphenols are released from lacquer by splitting C–C and C–O bonds between the aromatic ring and the phenolic oxygen of catechol or by cleavage of the hydroxyl group in the pyrolysis process [24]. Compounds with unsaturated chain such as 3-pentenyl-, 3-hexenyl, 3-heptenyl-, 3-octenyl-, 3-nonenyl-, 3-decenylcatechols and 3-octadienylcatechol which contains two double bonds were also found among pyrolysis products. Furthermore, tris-methylated 6-(2,3-dihydroxy)-hexanoic, 7-(2,3dihydroxy)-heptanoic, 8-(2,3-dihydroxy)-octanoic, 9-(2,3-dihydroxy)nonanoic acids were detected. It was found that these substances are formed during the oxidation of lacquers [22]. Along with these acids bis-methylated 8-(3-hydroxyphenyl)-octanoic and 9-(3hydroxyphenyl)-nonanoic acids were identified which are probably the products of the cleavage of C–O bonds between aromatic ring and phenolic oxygen of oxidized lacquer. Fig. 7b shows the extracted ion chromatogram of the ion with m/z 57, which characterized the content of aliphatic hydrocarbons in the products of pyrolysis. Hydrocarbons produced by cleaving C–C bonds between the aliphatic chain and the aromatic ring. The most intense peak in all extract ion chromatograms belongs to pentadecane, which corresponds to the chain of urushiol monomer. The appearance of tetradecene may be explained by splitting the C–C bonds between the side chain and the benzyl moiety [25]. 3.3.2. Fragments of drying oil The main substances which were identified in the pyrograms of lacquers are fragments of drying oils. They are represented by methylated fatty acids from hexanoic to eicosanoic. A small amount of unsaturated and dicarboxylic acids also presents in the pyrograms. The long chain

Fig. 6. The micrographs of the sample 29-22 under different magnifications (a ×100 and b ×1800).

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Table 3 List of compounds identified in the chromatogram of the lacquer samples, their retention times and molecular weights. Retention time, min

Compound

МW

4.58 8.22 11.34 11.92 14.11/14.86 14.32 15.38 15.83/16.35 15.96/16.24/16.29 16.46 17.27 17.46/18.61/18.82 17.56 18.04 18.21 18.27 18.38 18.93 19.11 19.38/19.71 19.78 19.92/21.02/21.28 20.05/20.12 20.1 20.28/20.35 20.76 21.22/22.39 21.33/21.58 21.94 21.98/22.25 22.04 22.21 22.32 22.89 23.03 23.03 23.27 23.61/23.8 24.02 24.18 24.26 24.28 24.63/25.61 24.67 24.98 25.28 25.51/25.60 25.87 26.19 27.19 27.32 27.36 28.09 28.21 28.31 28.39 28.42 28.82 29.05 29.19 29.42 29.72 29.89/30.13 30.18 30.19 30.64 30.71 31.05 31.06–31.17 31.30 31.33 31.51 31.66 31.75

Toluene Dimethylbenzene Methoxybenzene (anisol) Hexanoic acid (Me) Ethylmethylbenzene (isomers) Benzylmethylether Trimethylbenzene Isopropyl methylbenzene (isomers) Methylanisol (isomers) Heptanoic acid (Me) Butylbenzene Dimethylanisol (isomers) 1-Phenyl-1-propanone 2-Ethylmethoxybenzene Undecene Benzoic acid (Me) Undecane Octanoic acid (Me) Ethylanisol Dimethoxybenzene (isomers) 1-Methoxy-3-propylbenzene Dimethoxytoluen (isomers) Tetramethylmethoxybenzene (isomers) Naphthalene Isopropylanisol (isomers) Nonanoic acid (Me) Buthylcatechol (isomers) Methyldihydronaphthalene (isomers) Tridecane Methylnaphthalene (isomers) 3-(Methoxyphenyl)-propanol-1 Trimethoxybenzene Decanoic acid (Me) Pentylanisol Trimethoxybenzene Octylbenzene Tetradecene Dimethylnaphthalene (isomers) Octandioic acid (2Me) Methoxynaphthalene 7-Ethyltridecane-4,6-dion 2,6-Dimethyl-3,5-heptandion Methylmethoxy-naphthalene (isomers) Pentadecane Dodecanoic acid (Me) Nonandioic acid (2Me) Dimethylnaphthalenol (isomers) Dimethoxybenzoic acid (Me) 3-Hexylcatechol (2Me) Octylanisol Tetradecanoic acid (Me) Trimethoxybenzoic acid (Me) Methyltetradenoic acid (Me) Phenanthrene Anthracene Pentadecanoic acid (Me) 3-Octylcatechol (2Me) Hexadecenoic acid (Me) Methylpentadecanoic acid (Me) Hexadecenoic acid (Me) Hexadecanoic acid (Me) Methyl 6-(2,3-dimethoxyphenyl)-hexanoate methylhexadecanoic acid (Me) (isomers) Heptadecenoic acid (Me) Heptadecanoic acid (Me) 8-(3-Hydroxyphenyl)-octanoic acid (2Me) 6-(2,3-Dihydroxyphenyl) hexanoic acid (3Me) Fluoranthene Octadecenoic acid (Me) Pyrene Octadecanoic acid (Me) Octadecadienoic acid (Me) 8-(2,3-Dihydroxyphenyl) octanoic acid (3Me) Octadecadienoic acid (Me)

92 106 108 130 120 122 120 134 122 144 134 136 134 136 154 136 158 156 136 138 150 152 150 128 150 172 166 144 184 142 166 168 186 178 162 176 196 156 202 158 240 156 172 212 214 216 172 196 222 220 242 226 256 178 178 256 250 268 270 268 270 266 284 282 284 264 280 202 296 202 298 294 294 294

4-22

5-22

8-22

+ + + +

+

+

+

+ +

12-22

22-22

+ + + +

+ + + + + + + + + +

+ +

+

29-22

+

+ +

+

+

+

+

+

+

+

+

+

+

+

+ + + + + + + + + +

77-22

78-22

27-31

44-31

+ +

+

+ + +

+ + + + + + + + +

+ +

+ + +

+ + + + + +

+ + + + +

+ + + + +

+

+ + + + +

+

+ + + +

+

+ +

+ +

+

+

+ +

+

+

+

+ + +

+

+ + +

+

+

+

+

+

+

+ + +

+ + +

+ + +

+ +

+ + +

+ + +

+ + +

+

+ +

+ + + + + + +

+

+

+

+ + +

+

+

+ +

+ + + +

+ + + + + + + + + + +

+ + + +

+ + +

+ + + +

+

+

+ + + + +

+

+

+

+

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

+ + +

+

+

+

+

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

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

+ + +

+

+

+

+

+

+

+ +

+ + +

+ + +

+ + + +

+ +

+

+ + + + +

+ +

+

+ + +

+ + + + + + + +

+ +

+

+

+ + + +

+ + + +

+ + +

+

+ +

+ +

+

+ +

+ + + + + + + + +

+ + + + +

+ + +

+

+ + +

+

+ +

+ + + + +

+ + +

+

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

+ + +

+ + + +

+ + + + +

+

+

+ +

+

+

(continued on next page)

342

E. Karpova et al. / Microchemical Journal 130 (2017) 336–344

Table 3 (continued) Retention time, min

Compound

МW

4-22

31.89 32.16 32.22 32.42 32.65 32.68 32.71 32.85 32.85 33.07 33.08 33.30 33.36 33.37 33.43 33.49 33.50

Octadecadienoic acid (Me) Pimaric acid derivative Nonadecylic acid (Me) Rethen α-D-glucopyranoside, phenyl 2,3,4,6-tetra-O-methylDihydroabietic acid (Me) Octadecatrienoic acid (Me) Tetrahydroabietic acid (Me) Eicosenoic acid (Me) Pimaric acid (Me) Eicosanoic acid (Me) Isopimaric acid (Me) 4-Epi-dehydroabietinol acetate Dihydroabietinol acetate Dehydroabietic acid (Me) Dehydroabietinol acetate 7-Oxo-abietic acid (Me)

294 − 312 234 312 318 292 320 324 320 326 320 328 328 314 328 328

+ + +

saturated and unsaturated hydrocarbons are likely the degradation products of urushiol, though they may be the fragments of waxes. Peaks of methylated hexadecanoic, octadecanoic and octadecenoic acids are the most intense in pyrograms. The ratio of peak areas of the methylated hexadecanoic (palmitic) and octadecanoic (stearic) acids (P/S) in the pyrograms of the samples varies from 1.1 to 1.4. According to Wei et al. [26], the P/S ratios in linseed and tung oils are comparable and are 1.2. However, the presence of the peaks of unsaturated compounds in the pyrograms allows suggesting using of tung oil, because they are preserved in the unoxidized oil only, i.e. in oil, which was not pre-polymerized prior to use in order to accelerate the drying of the lacquer coating. Generally, drying oils such as linseed, flaxseed and hemp oils are heated before use; during this process the double bonds in the oil begin to polymerize. Unlike them tung oil does not require preheating to pre-polymerization and dries much faster because of conjugated double bonds of eleostearic acid. Thus, most likely tung oil was used in the manufacture of the analyzed lacquer wares. It should also be noted that the content of saturated acids which present in the lipid fraction of urushiol may affect on P/S ratio of the samples. No alkylcatechols and hydrocarbons were found in the pyrograms of the samples 5-22 (bordure on the edge of the umbrella) and 29-22 (a net of a headdress). Predominant pyrolysis products of these samples are fatty and dicarboxylic acids. This fact suggests that they were made on the basis of drying oil without an addition of urushiol. 3.3.3. Polycyclic aromatic hydrocarbon (PAH) Polycyclic aromatic hydrocarbons - naphthalene, anthracene, phenanthrene, pyrene and derivatives thereof were found in all analyzed samples except of 5-22 (bordure on the edge of the umbrella). Charcoal could be used as a black pigment for coloring of lacquers. Grinding of the

5-22

+

8-22

12-22

22-22

29-22

77-22

78-22

27-31

+

+

+ +

+

+

+

+ +

+ +

+ + +

+

+ +

+

+

44-31

+ +

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+

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surfaces of the intermediate lacquer layers with coal for obtaining smooth coating of the ware could be another source of polycyclic aromatic hydrocarbons. PAH are absent in the sample 5-22, so it probably consisted of the pigment (red ocher) mixed with drying oil only. 3.3.4. Resinous substances Resinous substances, which were found in lacquers, are diterpenoids - abietic acid derivatives, and pimaric and isopimaric acids. Abietic acid derivatives as well as pimaric and isopimaric acids were found in the samples 12-22 (coating of the chariot wheel spoke), 77-22 (an ornamental object), 78-22 (coating of the umbrella spokes), 22-22 (the worktop of the lacquer table) and in both cups. Such set of resin acids allows suggesting the use of colophony for obtaining gloss surfaces of the lacquer wares. No resinous substances were found in the lacquer coating of the chariot umbrella spokes and walls possibly due to poor preservation of these coatings. Also, no resin acids were found in the net of the headdress (29-22). This sample was preserved well enough, and the lack of resin in its composition is likely the requirement of manufacturing technology. 4. Conclusion The composition of the lacquer coatings of the lacquer wares from the 22nd and 31st Noin-Ula barrows was determined by FT-IR spectroscopy, SEM-EDS and pyrolysis coupled with gas chromatography/mass spectrometry. Urushiol components, drying oil (probably tung oil), diterpene resin (colophony), and polycyclic aromatic hydrocarbons (charcoal fragments) were identified in the lacquer compositions. Pigments to decorate the lacquer wares were iron oxides (in the composition of earth pigment and umber), cinnabar, and orpiment.

Fig. 7. The extract chromatogram of the ion with 136 m/z (a) and with m/z 57 (b) of the sample 77-22: (C10) decane; (C11: 1) undecene; (C11) undecane; (C12: 1) dodecene; (C12) dodecane; (C13: 1) tridecene; (C13) tridecane; (C14: 1) tetradecene; (C14) tetradecane; (C15: 1) pentadecene; and (C15) pentadecane.

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Table 4 List of compounds identified in extracted ion chromatogram of the ion with m/z 136 of the archaeological samples. №

Compound

Retention time

Most abundant m/z

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

C11H16O2 3-propylcatechol (2Me) C12H18O2 3-butylcatechol (2Me) C13H18O2 3-pentenylcatechol (2Me) C13H20O2 3-pentylcatechol (2Me) C14H22O 3-heptylphenol (Me) C14H20O2 3-hexenylcatechol (2Me) C14H22O2 3-hexylcatechol (2Me) C15H24O 3-octylphenol (1Me) C15H22O2 3-heptenylcatechol (2Me) C15H24O2 3-heptylcatechol (2Me) C16H24O 3-nonylcatechol (2Me) C16H22O2 3-octadienylcatechol (2Me) C16H24O2 3-octenylcatechol(2Me) C16H26O2 3-octylcatechol (2Me) C17H26O2 3-nonenylcatechol (2Me) C15H22O4 methyl 6-(2,3-dimethoxyphenyl)- hexanoate C18H28O2 3-decenylcatechol (2Me) C16H24O3 methyl 8-(3-methoxyphenyl)-octanoate C16H24O4 methyl 7-(2,3-dimethoxyphenyl)-heptanoate C17H26O3 methyl 9-(3-methoxyphenyl)-nonanoate C17H26O4 methyl 8-(2,3-dimethoxyphenyl)-octanoate C18H28O4 methyl 9-(2,3-dimethoxyphenyl)-nonanoate

22.46 23.79 24.94 25.02 26.02 26.11 26.19 27.19 27.24 27.33 28.22 28.29 28.33 28.42 29.65 29.72 30.48 30.64 30.71 31.46 31.65 32.55

136, 151, 166, 180 136, 156, 194 136, 151, 173, 189, 206 74, 87, 136, 208 91, 122, 135, 206 136, 151, 161, 204, 220 136, 152, 222 122, 139, 182, 220 122, 136, 165, 180, 234 74, 87, 136, 152, 236 122, 135, 150, 232 122, 136, 178,234,246 136, 187, 202, 248 136, 152, 168, 250 158, 192, 213, 228,262 88, 136, 151, 266 136, 151, 276 91, 122, 264 71, 136, 151, 280 136, 151,164, 278 91, 136, 152, 294 136, 151, 308

Coating of the chariot umbrella spokes likely did not contain pigments in its composition, except charcoal and its brown color is due to the color of lacquer itself. The pigment of the bordure on the edge of the umbrella was red ocher. Binder therein was drying oil. The base coating of the chariot walls was made with the addition of umber, as evidenced by iron and manganese compounds in its composition. Red decoration of the outer sides of the walls was made with cinnabar. The chariot wheel spokes were made in a similar way. The pigment of the lacquer worktop, hand umbrella spokes and cups were iron oxides. The patterns on the cup were made with cinnabar. The surface of the net of the headdress was covered with lead sulfide. Probably it has been decorated with the pigments based on oxides or any other lead compounds; however, these pigments were turned into black lead sulfide while the net was in the burial. Cinnabar and iron oxides determine red and brown color of the lacquer object with an ornament; orpiment gives yellow color to carved lines. This analytical study helps us to understand the technologies of the ancient Chinese masters. The manufacturing techniques of the lacquer wares involve the use of the different natural organic materials of plant origin (urushiol, drying oil, colophony) and of inorganic pigments. The whole process of the lacquer wares manufacturing was very complicated and lengthy. Acknowledgements This work was supported by the Russian Foundation for Basic Research [grant numbers 13-06-12026]. All spectral and analytical measurements were made at the Multi-Access Chemical Service Center SB RAS.

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