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mass spectrometry
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Investigation of Ryukyu lacquerwares by pyrolysis-gas chromatography/mass spectrometry Takayuki Honda a , Rong Lu a,∗ , Midori Yamabuki a , Daisuke Ando a , Masako Miyazato b , Kunio Yoshida c , Tetsuo Miyakoshi a a
Department of Applied Chemistry, Meiji University, 1-1-1 Higashimita, Tama-ku, Kawasaki-shi 214-8571, Japan Urasoe Art Museum, 1-9-2 Nakama, Urasoe-shi, Okinawa 901-2103, Japan c The University Museum, The University of Tokyo, 7-3-1 Hongo Bunkyo-ku, Tokyo 113-0033, Japan b
a r t i c l e
i n f o
Article history: Available online xxx Keywords: Ancient Lacquer species Cross-section Pigment
a b s t r a c t Two pieces of lacquer obtained from Ryukyu lacquerwares produced in the 17–19th century in the Ryukyu Kingdom belonging to the Urasoe Art Museum were analyzed by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). The results were compared with the standard of natural lacquer film to determine the identity of the lacquer species. Urushiol (MW = 320), 3-heptylcatechol (MW = 208), and 3-heptylphenol (MW = 192) were detected as pyrolysis products of lacquer pieces of a lacquer tray made by the hakue technique, suggesting that this Ryukyu lacquerware was coated with lacquer sap tapped from a Toxicodendron vernicifluum lacquer tree. On the other hand, urushiol (MW = 320), 3heptylcatechol (MW = 208), 3-heptylphenol (MW = 192), laccol (MW = 348), 3-nonylcatechol (MW = 236), and 3-nonylphenol (MW = 220) were detected as pyrolysis products of lacquer pieces from a dinner tray made by the mitsuda-e technique, suggesting that this Ryukyu lacquerware was coated with mixture lacquer sap tapped from T. vernicifluum and Toxicodendron succedanea lacquer trees, respectively. Moreover, microscopy and cross-section studies demonstrated that the lacquers had a multi-layer structure. X-ray analytical microscopy was carried out directly on the surface of lacquerwares to determine the presence of different pigments. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Lacquer, is a unique process in Asia that uses sap tapped from lacquer trees grown wild or cultivated in areas of East Asia such as China, Korea, and Japan (including the Ryukyu islands) to Southeast Asia such as Myanmar, Thailand, Laos, Cambodia, and Vietnam and has been used to prepare crafts or wares for more than 7000 years [1,2]. The surfaces of objects made of wood, bamboo, cloth, paper, porcelain, leather, and metal are coated with lacquer sap not only for protection but also for esthetic effect. Despite difference in the nations, languages, and customs in Asian countries, the interlinked lacquer cultures demonstrate interrelationships and are also part of modern life [3]. Okinawa, located in southernmost Japan, has a nearly 500-year history as the Ryukyu Kingdom and has a Ryukyu lacquer culture with its own characteristics (Fig. 1). During its history, the Ryukyu Kingdom maintained good relations with both China and Japan
∗ Corresponding author. Tel: +81-44-934-7784. E-mail address: [email protected] (R. Lu).
and also traded with Southeast Asian countries. Ryukyu people actively imported neighboring countries’ cultures and technology into their own culture via trade activities and formed a new culture characterized by complex cultural elements. Therefore, we find similar materials and techniques to those of Chinese, Japanese, and Southeast Asian countries in the lacquer crafts. That is, the history of Ryukyu lacquerware overlaps with the history of the Ryukyu Kingdom, and clarification of Ryukyu lacquer crafts will increase understanding of the history and culture of Okinawa. In addition, identification of lacquer species is important in the conservation and restoration of valuable ancient Ryukyu lacquerwares. Previously, we analyzed six kinds of Ryukyu lacquerwares belonging to the Urasoe Art Museum by Py-GC/MS [4], and urushiol and laccol pyrolysis products were detected, suggesting that the six lacquerwares were prepared using Toxicodendron vernicifluum and/or Toxicodendron succedanea. Many research results [5–7] have shown that analytical pyrolysis is an effective method for characterization of lacquer film. In this study, one piece from a lacquer box using the hakue technique (a technique in which a design is first carved on an object’s surface and coated with lacquer sap, and then gold or silver leaf is affixed. When completely dry, it is
http://dx.doi.org/10.1016/j.jaap.2014.09.026 0165-2370/© 2014 Elsevier B.V. All rights reserved.
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measurements were carried out in air, and the lifetime of 100 s for each spectrum was chosen.
2.3. Py-GC/MS measurement Pyrolysis-gas chromatography/mass spectrometry measurements were carried out using a vertical micro furnace-type pyrolyzer PY-2020iD (Frontier Lab, Japan), a Hewlett-Packard 6890 gas chromatograph, and a HPG 5972A (Hewlett-Packard, Ltd.) mass spectrometer. A stainless steel capillary column (0.25 mm i.d. × 30 m) coated with 0.25 m of Ultra Alloy PY-1 (100% methylsilicone) was used for the separation. The sample (0.05 mg) was placed in a platinum sample cup. The cup was placed on top of the pyrolyzer at near ambient temperature. The sample cup was introduced into the furnace at 500 ◦ C, and then the temperature program of the gas chromatograph oven was started. The gas chromatograph oven was programmed to provide a constant temperature increase of 12 ◦ C per min from 40 ◦ C to 500 ◦ C, and then hold for 10 min at 500 ◦ C. The flow rate of the helium gas was 1 ml/min. All pyrolysis products were identified by mass spectrometry. The mass spectrometry ionization energy was 70 eV (EI-mode). Fig. 1. Location of Ryukyu Islands in Japan.
polished, and a gold or silver image, called a foil picture, shows). One piece made by the mitsuda-e technique (a lacquer painting decoration technique using oil, like oil painting techniques) of Ryukyu lacquerwares belonging to the Urasoe Art Museum was analyzed by cross-section, X-ray analytical microscopy, and Py-GC/MS. Based on the results, Ryukyu lacquer technology, coloring agents, and characteristics are discussed. 2. Experimental One piece sample of mitsuda-e lacquer film (A) and one piece of hakue (B) lacquerware belonging to the Urasoe Art Museum of Japan were analyzed in this study. The objects are shown in Fig. 2. 2.1. Cross-section analysis Scientific analysis of the surface coating is important for identifying the origin and characteristics of coating materials as well as for future conservation. In this study, cross-section analysis was carried out using a polished thin-section method [8] for observation in a camera-attached optical microscope (VHX-1000 digital microscope, Keyence Co. Ltd., Tokyo, Japan, and Nikon Digital Camera DXM 1200F, Japan) and scanning electron microscope (SEM). The detailed method was as follows. Each lacquer sample was first divided into several approximately 2.5–4.0 mm pieces, and then embedded in epoxy resin (Adeka resin EP-4200A: Adeka hardening agent EH-4332 = 5:2). After the epoxy resin had completely hardened, the surfaces of the embedded samples were ground flat and polished with wet sandpaper. The upper surfaces were observed with a stereoscopic or metallurgical microscope. In addition, the other side of the sample was ground and polished until it was approximately 10–15 m in thickness and then observed using an optical microscope and SEM. 2.2. X-ray fluorescence analysis (XRF) XRF was performed using an X-ray analytical microscope system (XGT-5200, Horiba Co., Ltd., Tokyo, Japan). The tube voltage and current were set at 50 kV and 1.0 mA, respectively. The
2.4.
87 Sr/86 Sr
isotope ratio measurement
2.4.1. Reagents Special grade nitric acid, perchloric acid, ammonium acetate, and hydrogen peroxide were purchased from Kanto Chemical Co., Ltd. in Tokyo, Japan, and used directly.
2.4.2. Sample treatment and separation of strontium Thirty micrograms of the lacquer sample was treated with 6 ml of 14 M nitric acid at 120 ◦ C for 11 h in a Teflon beaker with a lid to dissolve the organic matter, and the lid was opened in dry heat to remove the organic matter. Then 5 ml of 14 M nitric acid, 0.5 ml perchloric acid, and 0.5 ml hydrogen peroxide were added to the beaker and continuously heated at 120 ◦ C for 9 h covered, and then the lid was opened in dry heat to remove the organic matter. This operation was repeated at least four times in order to completely remove the organic matter. Then 1 ml of 7 M nitric acid was added to the sample and shaken to dissolve it in nitric acid; this was called sample I. Sr resin (0.5 ml, particles: 50–100 m, Eichrom Co., Ltd., USA) was added to a prepackaged column, and washed with 15 ml of 2% nitric acid and 4 ml of 3 M nitric acid in order to eliminate Sr residues. One milliliter of sample I was added to this column and eluted with nitric acid in the order of (1) 3 M, 10 ml, (2) 7 M, 6 ml, and (3) 3 M, 2 ml to eliminate other elements, and finally eluted with 7.5 ml of 2% nitric acid to collect Sr; this was called sample II.
2.4.3. Inductively coupled plasma mass spectrometry Sample II was analyzed by isoprobe multicollector inductively coupled plasma mass spectrometry (ICP-MS, Micromass Ltd., UK); mass numbers of 83 Kr, 84 Sr, 85 Rb, 86 Sr, 87 Sr, and 88 Sr were measured. The 84 Kr and 86 Kr signal strength were estimated from the 83 Kr signal strength, and the 84 Sr and 86 Sr signal strengths were corrected based on the 84 Kr and 86 Kr signal strengths. Similarly, the signal strength of the 86 Rb was estimated from 85 Rb signal strength, and the signal strength of 87 Sr was corrected based on the 86 Rb signal strength. The internal standard control was 50 ppb NIST SRM 987 (strontium carbonate, 87 Sr/86 Sr = 0.71025).
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Fig. 2. Lacquerware samples.
Fig. 3. Cross-section photomicrograph of sample A (left) and its layer image (right).
3. Results and discussion 3.1. Cross-section analysis A micrograph of cross-sections of sample A is shown in Fig. 3 (left). It has a four-layer structure with vermilion (HgS) as the red pigment. The energy dispersive X-ray spectrometry (EDX) analysis showed that the pigment layer was about 95% Hg (HgS), <1% As (As2 S3 ), <1% Pb (PbO), <1% Fe (Fe2 O3 ), and 4% Ca (CaCO3 ), respectively. The image of the layer structure shown in Fig. 3 (right), a mineral powder containing Fe, Ca, and others were used as shitachi (surface treatment), coated with a lacquer layer about 80 m thick, and then coated with a red color layer with HgS mixed into the lacquer, making it about 70 m thick. Finally, the top coating used the mitsuda-e technique, which uses oil, pigments, vermilion, orpiment, gold powder, and gold foil to create a lacquerware about 10 m thick. Fig. 4 is a cross-section micrograph of sample B showing its three-layer structure. The EDX analysis showed that the pigment layer was about 68% Hg (HgS), 10% Fe (Fe2 O3 ), and 20% Ca (CaCO3 ).
An image of the layer structure is shown in Fig. 4 (right); a mineral powder containing Fe, Ca, and others was used as shitachi (surface treatment), then it was coated with a lacquer layer mixed with vermilion, and then the top coating using hakue technique, which first used HgS to produce a red color, then used gold powder and gold foil to design an image. The thickness is about 80 m. 3.2. Pyrolysis GC–MS analysis The m/z = 108 chromatogram of sample A obtained by direct pyrolysis GC–MS is shown in Fig. 5. 3-heptylphenol (C7), 3-nonylphenol (C9), 3-pentadecylphenol (C15), and 3heptadecylphenol (C17) were detected. Compared with the standard lacquer, it can be concluded that the coating material of sample A is lacquer from T. vernicifluum and T. succedanea lacquer trees. However, because the urushiol also contains a few C17 in the side chain, in order to confirm the urushiol and laccol structures, methylation of the hydroxyl group by tetramethylammonium hydroxide (TMAH) was carried out to suppress alterations of the component ratio, and the results shown in Fig. 6.
Fig. 4. Cross-section photomicrograph of sample B (left) and its layer image (right).
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C7: 3-heptylphenol C9: 3-nonylphenol C15: 5.00
10.00
15.00
20.00
C17: 25.00
30.00
Fig. 5. Chromatogram (m/z = 108) of sample A by direct pyrolysis GC–MS.
Fig. 6 shows that urushiol dimethyl ether (Fig. 6A, MW = 348) and laccol dimethyl ether (Fig. 6B, MW = 376) were detected, confirming that the mitsuda-e lacquerware is coated with a mixture of lacquer saps tapped from urushiol and laccol lacquer trees.
Because a drying oil is usually used in the mitsuda-e technique, the m/z = 60 chromatogram of sample A obtained by direct pyrolysis GC–MS also was analyzed. Palmitic acid and stearic acid oils and 1, 6-anhydoro--D-glucopyranose, which results from thermal decomposition of starch, fiber, and/or rice paste, were detected, as shown in Fig. 7. In general, drying oil is added to increase the luster and elasticity of the lacquer film, and the starch, fiber, and/or rice paste is used not only to increase the intensity and stickiness of the lacquer film but also to reduce the consumption of lacquer sap. Fig. 8 shows the m/z = 202 and 299.6 mass chromatograms of sample A obtained by direct pyrolysis GC–MS. In the Py-GC/MS measurement, HgS was broken down into Hg and S by heating, and Hg was detected. In nature, the isotopes of Hg are 196 (0.15%), 198 (9.97%), 199 (16.87%), 200 (23.1%), 201 (13.18%), 202 (29.86%), and 204 (6.87%), respectively. Like HgS, elementary As of As2 S3 was detected at m/z = 74.9 for 1 × As, m/z = 149.8 for 2 × As, m/z = 224.7 for 3 × As, and m/z = 299.6 for 4× As in the mass spectrometry of sample A [9]. That is, in the mitsuda-e Ryukyu lacquerware, cinnabar was used as a red pigment and As2 S3 was used as a yellow-green pigment. The pyrolysis GC–MS spectrum of sample B is shown in Fig. 9. Unlike sample A, only 3-heptylphenol was detected. The coating
Fig. 6. Mass chromatograms of urushiol (A) and laccol (B) reacted with TMAH.
Palmitic acid Stearic acid
5.00
10.00 0
15.00
20.00 2
25.00
30.00
Fig. 7. Chromatogram (m/z = 60) of sample A by direct pyrolysis GC–MS.
Fig. 8. Mass spectrometry of (A) Hg and (B) As of sample A.
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C7: 3-heptylphenol C15 Fig. 9. Pyrolysis GC–MS chromatogram (m/z = 108) of sample B.
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Prefecture (IWP), Fukushima Prefecture (FKP), Ibaraki Prefecture (IBP), Kyoto Prefecture (KTP), and Okayama Prefecture (OKP) of Japan; the Shanxi, Hubei, Guizhou, and Sichuan Provinces of China, and the hakue sample (䊉). It can be seen that the 87 Sr/86 Sr isotope ratios of Japanese lacquer are lower than 0.710, but those of the continental Chinese mainland are higher than 0.712. The 87 Sr/86 Sr isotope ratio of hakue is 0.7137, higher than 0.710, suggesting that this Ryukyu hakue lacquerware is made of lacquer sap tapped from a lacquer tree grown in the Chinese mainland. Lacquer originated in China, and it was considered that the lacquer technology and lacquer tree came from Chinese mainland through the Korean Peninsula to Japan; in other words, the Japanese lacquer tree is an imported plant. Historically, Ryukyu was an independent kingdom, and had much trade with the surrounding countries, especially China. Our result also demonstrates the prosperous trade of the Ryukyu Kingdom. 4. Conclusion The analysis results of Ryukyu mitsuda-e and hakue lacquerwares showed that lacquer sap tapped from T. vernicifluum and T. succedanea lacquer trees grown on the Asian continent were used alone and/or combined as a coating material. Ryukyu was an independent kingdom at same points in its history and traded very actively with surrounding countries. The analysis results of this study confirmed that Ryukyu people efficiently used the imported coating materials alone or in a mixture to make lacquerwares using many techniques, such as mitsuda-e and hakue. Acknowledgement
Fig. 10. Strontium isotope ratios of Japanese, Chinese, and hakue lacquers.
material of sample B was collected from a T. vernicifluum lacquer tree. Like sample A, palmitic acid and stearic acid were also detected in the m/z = 60 chromatogram, suggesting that the hakue technique also used drying oil to increase the luster and elasticity of a lacquer film. 3.3. Sr isotopes ratio It has known that the Sr isotope ratio of the ancient Chinese mainland is higher than that of the relatively young Japanese islands, and the ratio has been used to identify the provenance of green onions in Japan [10]. We have measured the strontium isotope ratio of lacquer films from various origins of China and Japan, and found that all Chinese lacquer films have an 87 Sr/86 Sr isotope ratio over 0.711, and Japanese lacquer films have a ratio lower than 0.710; the borderline is around 87 Sr/86 Sr = 0.710. In order to identify the lacquer of mitsuda-e and hakue samples in this study, we also tried to analyze the 87 Sr/86 Sr isotope ratio. However, because the lacquer sap used in the mitsuda-e sample is a mixture of urushiol and laccol and laccol lacquer trees are mainly grown in Vietnam, which belongs to the Asian mainland, we predicted that its 87 Sr/86 Sr isotope ratio should more than 0.710; therefore, we measured the 87 Sr/86 Sr isotope ratio of only the hakue sample, and the results are shown in Fig. 10. Fig. 10 shows the 87 Sr/86 Sr isotope ratio results of lacquer sap tapped from lacquer trees grown in Hokkaido (HKD), Iwate
This work was financially supported in part by a Grant-in-Aid for Scientific Research on Innovative Areas from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan and by the cooperative research program of the MEXT-Supported Program for the Strategic Research Foundation at Private University. References [1] T. Miyakoshi, K. Nagase, T. Yoshida, Progress of Lacquer Chemistry, IPC Publisher, Tokyo, Japan, 1999. [2] T. Terada, K. Oda, H. Oyabu, T. Asami, Lacquer — the Science and Practice, Rikou Publisher, Tokyo, Japan, 1999. [3] R. Lu, T. Yoshida, T. Miyakoshi, Oriental lacquer: a natural polymer, Polym. Rev. 53 (2013) 153–191. [4] R. Lu, X-M. Ma, Y. Kamiya, T. Honda, Y. Kamiya, A. Okamoto, T. Miyakoshi, Identification of Ryukyu lacquerware by pyrolysis–gas chromatography/mass spectrometry, J. Anal. Appl. Pyrolysis 80 (2007) 101–110. [5] R. Lu, Y. Kamiya, T. Miyakoshi, Applied analysis of lacquer films based on pyrolysis-gas chromatography/mass spectrometry, Talanta 70 (2006) 370–376. [6] M. Tsukagoshi, Y. Kitahara, S. Takahashi, T. Tsugoshi, T. Fujii, Characterization of Japanese lacquer liquid and films by means of evolved gas analysis-ion attachment mass spectrometry, Anal. Methods 3 (2011) 1943–1947. [7] M. Tsukagoshi, Y. Kitahara, S. Takahashi, T. Fujii, Pyrolysis analysis of Japanese lacquer films: direct probe-Li+ ion attachment mass spectrometry versus pyrolysis/gas chromatography/mass spectrometry, J. Anal. Appl. Pyrolysis 95 (2012) 156–163. [8] F. Okada, in: K. Michael (Ed.), A Study on the Structure of the Coating film of Urushiware at the Linden-Museum, Stuttgart, Japanese and European Lacquerware: Adoption-Conservation, Bayerischen Landesamtes fur Denkmalpflege, Munich, 2000, pp. 135–146. [9] X.-M. Ma, R. Lu, T. Miyakoshi, Application of pyrolysis gas chromatography/mass spectrometry in lacquer research: a review, Polymers 6 (2014) 132–144. [10] Ministry of Agriculture, Forestry and Fisheries of Japan, Development of Techniques for Determination of the Variety and the Geographic Provenance of Agricultural Products by Using Analysis of Minor Elements and DNA maKers, Agriculture, Forestry and Fisheries Research Council Secretariat of Japan, 2005.
Please cite this article in press as: T. Honda, et al., Investigation of Ryukyu lacquerwares by pyrolysis-gas chromatography/mass spectrometry, J. Anal. Appl. Pyrol. (2014), http://dx.doi.org/10.1016/j.jaap.2014.09.026
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Investigation of Ryukyu lacquerwares by pyrolysis-gas chromatography/mass spectrometry Takayuki Honda a , Rong Lu a,∗ , Midori Yamabuki a , Daisuke Ando a , Masako Miyazato b , Kunio Yoshida c , Tetsuo Miyakoshi a a
Department of Applied Chemistry, Meiji University, 1-1-1 Higashimita, Tama-ku, Kawasaki-shi 214-8571, Japan Urasoe Art Museum, 1-9-2 Nakama, Urasoe-shi, Okinawa 901-2103, Japan c The University Museum, The University of Tokyo, 7-3-1 Hongo Bunkyo-ku, Tokyo 113-0033, Japan b
a r t i c l e
i n f o
Article history: Available online xxx Keywords: Ancient Lacquer species Cross-section Pigment
a b s t r a c t Two pieces of lacquer obtained from Ryukyu lacquerwares produced in the 17–19th century in the Ryukyu Kingdom belonging to the Urasoe Art Museum were analyzed by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). The results were compared with the standard of natural lacquer film to determine the identity of the lacquer species. Urushiol (MW = 320), 3-heptylcatechol (MW = 208), and 3-heptylphenol (MW = 192) were detected as pyrolysis products of lacquer pieces of a lacquer tray made by the hakue technique, suggesting that this Ryukyu lacquerware was coated with lacquer sap tapped from a Toxicodendron vernicifluum lacquer tree. On the other hand, urushiol (MW = 320), 3heptylcatechol (MW = 208), 3-heptylphenol (MW = 192), laccol (MW = 348), 3-nonylcatechol (MW = 236), and 3-nonylphenol (MW = 220) were detected as pyrolysis products of lacquer pieces from a dinner tray made by the mitsuda-e technique, suggesting that this Ryukyu lacquerware was coated with mixture lacquer sap tapped from T. vernicifluum and Toxicodendron succedanea lacquer trees, respectively. Moreover, microscopy and cross-section studies demonstrated that the lacquers had a multi-layer structure. X-ray analytical microscopy was carried out directly on the surface of lacquerwares to determine the presence of different pigments. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Lacquer, is a unique process in Asia that uses sap tapped from lacquer trees grown wild or cultivated in areas of East Asia such as China, Korea, and Japan (including the Ryukyu islands) to Southeast Asia such as Myanmar, Thailand, Laos, Cambodia, and Vietnam and has been used to prepare crafts or wares for more than 7000 years [1,2]. The surfaces of objects made of wood, bamboo, cloth, paper, porcelain, leather, and metal are coated with lacquer sap not only for protection but also for esthetic effect. Despite difference in the nations, languages, and customs in Asian countries, the interlinked lacquer cultures demonstrate interrelationships and are also part of modern life [3]. Okinawa, located in southernmost Japan, has a nearly 500-year history as the Ryukyu Kingdom and has a Ryukyu lacquer culture with its own characteristics (Fig. 1). During its history, the Ryukyu Kingdom maintained good relations with both China and Japan
∗ Corresponding author. Tel: +81-44-934-7784. E-mail address: [email protected] (R. Lu).
and also traded with Southeast Asian countries. Ryukyu people actively imported neighboring countries’ cultures and technology into their own culture via trade activities and formed a new culture characterized by complex cultural elements. Therefore, we find similar materials and techniques to those of Chinese, Japanese, and Southeast Asian countries in the lacquer crafts. That is, the history of Ryukyu lacquerware overlaps with the history of the Ryukyu Kingdom, and clarification of Ryukyu lacquer crafts will increase understanding of the history and culture of Okinawa. In addition, identification of lacquer species is important in the conservation and restoration of valuable ancient Ryukyu lacquerwares. Previously, we analyzed six kinds of Ryukyu lacquerwares belonging to the Urasoe Art Museum by Py-GC/MS [4], and urushiol and laccol pyrolysis products were detected, suggesting that the six lacquerwares were prepared using Toxicodendron vernicifluum and/or Toxicodendron succedanea. Many research results [5–7] have shown that analytical pyrolysis is an effective method for characterization of lacquer film. In this study, one piece from a lacquer box using the hakue technique (a technique in which a design is first carved on an object’s surface and coated with lacquer sap, and then gold or silver leaf is affixed. When completely dry, it is
http://dx.doi.org/10.1016/j.jaap.2014.09.026 0165-2370/© 2014 Elsevier B.V. All rights reserved.
Please cite this article in press as: T. Honda, et al., Investigation of Ryukyu lacquerwares by pyrolysis-gas chromatography/mass spectrometry, J. Anal. Appl. Pyrol. (2014), http://dx.doi.org/10.1016/j.jaap.2014.09.026
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measurements were carried out in air, and the lifetime of 100 s for each spectrum was chosen.
2.3. Py-GC/MS measurement Pyrolysis-gas chromatography/mass spectrometry measurements were carried out using a vertical micro furnace-type pyrolyzer PY-2020iD (Frontier Lab, Japan), a Hewlett-Packard 6890 gas chromatograph, and a HPG 5972A (Hewlett-Packard, Ltd.) mass spectrometer. A stainless steel capillary column (0.25 mm i.d. × 30 m) coated with 0.25 m of Ultra Alloy PY-1 (100% methylsilicone) was used for the separation. The sample (0.05 mg) was placed in a platinum sample cup. The cup was placed on top of the pyrolyzer at near ambient temperature. The sample cup was introduced into the furnace at 500 ◦ C, and then the temperature program of the gas chromatograph oven was started. The gas chromatograph oven was programmed to provide a constant temperature increase of 12 ◦ C per min from 40 ◦ C to 500 ◦ C, and then hold for 10 min at 500 ◦ C. The flow rate of the helium gas was 1 ml/min. All pyrolysis products were identified by mass spectrometry. The mass spectrometry ionization energy was 70 eV (EI-mode). Fig. 1. Location of Ryukyu Islands in Japan.
polished, and a gold or silver image, called a foil picture, shows). One piece made by the mitsuda-e technique (a lacquer painting decoration technique using oil, like oil painting techniques) of Ryukyu lacquerwares belonging to the Urasoe Art Museum was analyzed by cross-section, X-ray analytical microscopy, and Py-GC/MS. Based on the results, Ryukyu lacquer technology, coloring agents, and characteristics are discussed. 2. Experimental One piece sample of mitsuda-e lacquer film (A) and one piece of hakue (B) lacquerware belonging to the Urasoe Art Museum of Japan were analyzed in this study. The objects are shown in Fig. 2. 2.1. Cross-section analysis Scientific analysis of the surface coating is important for identifying the origin and characteristics of coating materials as well as for future conservation. In this study, cross-section analysis was carried out using a polished thin-section method [8] for observation in a camera-attached optical microscope (VHX-1000 digital microscope, Keyence Co. Ltd., Tokyo, Japan, and Nikon Digital Camera DXM 1200F, Japan) and scanning electron microscope (SEM). The detailed method was as follows. Each lacquer sample was first divided into several approximately 2.5–4.0 mm pieces, and then embedded in epoxy resin (Adeka resin EP-4200A: Adeka hardening agent EH-4332 = 5:2). After the epoxy resin had completely hardened, the surfaces of the embedded samples were ground flat and polished with wet sandpaper. The upper surfaces were observed with a stereoscopic or metallurgical microscope. In addition, the other side of the sample was ground and polished until it was approximately 10–15 m in thickness and then observed using an optical microscope and SEM. 2.2. X-ray fluorescence analysis (XRF) XRF was performed using an X-ray analytical microscope system (XGT-5200, Horiba Co., Ltd., Tokyo, Japan). The tube voltage and current were set at 50 kV and 1.0 mA, respectively. The
2.4.
87 Sr/86 Sr
isotope ratio measurement
2.4.1. Reagents Special grade nitric acid, perchloric acid, ammonium acetate, and hydrogen peroxide were purchased from Kanto Chemical Co., Ltd. in Tokyo, Japan, and used directly.
2.4.2. Sample treatment and separation of strontium Thirty micrograms of the lacquer sample was treated with 6 ml of 14 M nitric acid at 120 ◦ C for 11 h in a Teflon beaker with a lid to dissolve the organic matter, and the lid was opened in dry heat to remove the organic matter. Then 5 ml of 14 M nitric acid, 0.5 ml perchloric acid, and 0.5 ml hydrogen peroxide were added to the beaker and continuously heated at 120 ◦ C for 9 h covered, and then the lid was opened in dry heat to remove the organic matter. This operation was repeated at least four times in order to completely remove the organic matter. Then 1 ml of 7 M nitric acid was added to the sample and shaken to dissolve it in nitric acid; this was called sample I. Sr resin (0.5 ml, particles: 50–100 m, Eichrom Co., Ltd., USA) was added to a prepackaged column, and washed with 15 ml of 2% nitric acid and 4 ml of 3 M nitric acid in order to eliminate Sr residues. One milliliter of sample I was added to this column and eluted with nitric acid in the order of (1) 3 M, 10 ml, (2) 7 M, 6 ml, and (3) 3 M, 2 ml to eliminate other elements, and finally eluted with 7.5 ml of 2% nitric acid to collect Sr; this was called sample II.
2.4.3. Inductively coupled plasma mass spectrometry Sample II was analyzed by isoprobe multicollector inductively coupled plasma mass spectrometry (ICP-MS, Micromass Ltd., UK); mass numbers of 83 Kr, 84 Sr, 85 Rb, 86 Sr, 87 Sr, and 88 Sr were measured. The 84 Kr and 86 Kr signal strength were estimated from the 83 Kr signal strength, and the 84 Sr and 86 Sr signal strengths were corrected based on the 84 Kr and 86 Kr signal strengths. Similarly, the signal strength of the 86 Rb was estimated from 85 Rb signal strength, and the signal strength of 87 Sr was corrected based on the 86 Rb signal strength. The internal standard control was 50 ppb NIST SRM 987 (strontium carbonate, 87 Sr/86 Sr = 0.71025).
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Fig. 2. Lacquerware samples.
Fig. 3. Cross-section photomicrograph of sample A (left) and its layer image (right).
3. Results and discussion 3.1. Cross-section analysis A micrograph of cross-sections of sample A is shown in Fig. 3 (left). It has a four-layer structure with vermilion (HgS) as the red pigment. The energy dispersive X-ray spectrometry (EDX) analysis showed that the pigment layer was about 95% Hg (HgS), <1% As (As2 S3 ), <1% Pb (PbO), <1% Fe (Fe2 O3 ), and 4% Ca (CaCO3 ), respectively. The image of the layer structure shown in Fig. 3 (right), a mineral powder containing Fe, Ca, and others were used as shitachi (surface treatment), coated with a lacquer layer about 80 m thick, and then coated with a red color layer with HgS mixed into the lacquer, making it about 70 m thick. Finally, the top coating used the mitsuda-e technique, which uses oil, pigments, vermilion, orpiment, gold powder, and gold foil to create a lacquerware about 10 m thick. Fig. 4 is a cross-section micrograph of sample B showing its three-layer structure. The EDX analysis showed that the pigment layer was about 68% Hg (HgS), 10% Fe (Fe2 O3 ), and 20% Ca (CaCO3 ).
An image of the layer structure is shown in Fig. 4 (right); a mineral powder containing Fe, Ca, and others was used as shitachi (surface treatment), then it was coated with a lacquer layer mixed with vermilion, and then the top coating using hakue technique, which first used HgS to produce a red color, then used gold powder and gold foil to design an image. The thickness is about 80 m. 3.2. Pyrolysis GC–MS analysis The m/z = 108 chromatogram of sample A obtained by direct pyrolysis GC–MS is shown in Fig. 5. 3-heptylphenol (C7), 3-nonylphenol (C9), 3-pentadecylphenol (C15), and 3heptadecylphenol (C17) were detected. Compared with the standard lacquer, it can be concluded that the coating material of sample A is lacquer from T. vernicifluum and T. succedanea lacquer trees. However, because the urushiol also contains a few C17 in the side chain, in order to confirm the urushiol and laccol structures, methylation of the hydroxyl group by tetramethylammonium hydroxide (TMAH) was carried out to suppress alterations of the component ratio, and the results shown in Fig. 6.
Fig. 4. Cross-section photomicrograph of sample B (left) and its layer image (right).
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C7: 3-heptylphenol C9: 3-nonylphenol C15: 5.00
10.00
15.00
20.00
C17: 25.00
30.00
Fig. 5. Chromatogram (m/z = 108) of sample A by direct pyrolysis GC–MS.
Fig. 6 shows that urushiol dimethyl ether (Fig. 6A, MW = 348) and laccol dimethyl ether (Fig. 6B, MW = 376) were detected, confirming that the mitsuda-e lacquerware is coated with a mixture of lacquer saps tapped from urushiol and laccol lacquer trees.
Because a drying oil is usually used in the mitsuda-e technique, the m/z = 60 chromatogram of sample A obtained by direct pyrolysis GC–MS also was analyzed. Palmitic acid and stearic acid oils and 1, 6-anhydoro--D-glucopyranose, which results from thermal decomposition of starch, fiber, and/or rice paste, were detected, as shown in Fig. 7. In general, drying oil is added to increase the luster and elasticity of the lacquer film, and the starch, fiber, and/or rice paste is used not only to increase the intensity and stickiness of the lacquer film but also to reduce the consumption of lacquer sap. Fig. 8 shows the m/z = 202 and 299.6 mass chromatograms of sample A obtained by direct pyrolysis GC–MS. In the Py-GC/MS measurement, HgS was broken down into Hg and S by heating, and Hg was detected. In nature, the isotopes of Hg are 196 (0.15%), 198 (9.97%), 199 (16.87%), 200 (23.1%), 201 (13.18%), 202 (29.86%), and 204 (6.87%), respectively. Like HgS, elementary As of As2 S3 was detected at m/z = 74.9 for 1 × As, m/z = 149.8 for 2 × As, m/z = 224.7 for 3 × As, and m/z = 299.6 for 4× As in the mass spectrometry of sample A [9]. That is, in the mitsuda-e Ryukyu lacquerware, cinnabar was used as a red pigment and As2 S3 was used as a yellow-green pigment. The pyrolysis GC–MS spectrum of sample B is shown in Fig. 9. Unlike sample A, only 3-heptylphenol was detected. The coating
Fig. 6. Mass chromatograms of urushiol (A) and laccol (B) reacted with TMAH.
Palmitic acid Stearic acid
5.00
10.00 0
15.00
20.00 2
25.00
30.00
Fig. 7. Chromatogram (m/z = 60) of sample A by direct pyrolysis GC–MS.
Fig. 8. Mass spectrometry of (A) Hg and (B) As of sample A.
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C7: 3-heptylphenol C15 Fig. 9. Pyrolysis GC–MS chromatogram (m/z = 108) of sample B.
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Prefecture (IWP), Fukushima Prefecture (FKP), Ibaraki Prefecture (IBP), Kyoto Prefecture (KTP), and Okayama Prefecture (OKP) of Japan; the Shanxi, Hubei, Guizhou, and Sichuan Provinces of China, and the hakue sample (䊉). It can be seen that the 87 Sr/86 Sr isotope ratios of Japanese lacquer are lower than 0.710, but those of the continental Chinese mainland are higher than 0.712. The 87 Sr/86 Sr isotope ratio of hakue is 0.7137, higher than 0.710, suggesting that this Ryukyu hakue lacquerware is made of lacquer sap tapped from a lacquer tree grown in the Chinese mainland. Lacquer originated in China, and it was considered that the lacquer technology and lacquer tree came from Chinese mainland through the Korean Peninsula to Japan; in other words, the Japanese lacquer tree is an imported plant. Historically, Ryukyu was an independent kingdom, and had much trade with the surrounding countries, especially China. Our result also demonstrates the prosperous trade of the Ryukyu Kingdom. 4. Conclusion The analysis results of Ryukyu mitsuda-e and hakue lacquerwares showed that lacquer sap tapped from T. vernicifluum and T. succedanea lacquer trees grown on the Asian continent were used alone and/or combined as a coating material. Ryukyu was an independent kingdom at same points in its history and traded very actively with surrounding countries. The analysis results of this study confirmed that Ryukyu people efficiently used the imported coating materials alone or in a mixture to make lacquerwares using many techniques, such as mitsuda-e and hakue. Acknowledgement
Fig. 10. Strontium isotope ratios of Japanese, Chinese, and hakue lacquers.
material of sample B was collected from a T. vernicifluum lacquer tree. Like sample A, palmitic acid and stearic acid were also detected in the m/z = 60 chromatogram, suggesting that the hakue technique also used drying oil to increase the luster and elasticity of a lacquer film. 3.3. Sr isotopes ratio It has known that the Sr isotope ratio of the ancient Chinese mainland is higher than that of the relatively young Japanese islands, and the ratio has been used to identify the provenance of green onions in Japan [10]. We have measured the strontium isotope ratio of lacquer films from various origins of China and Japan, and found that all Chinese lacquer films have an 87 Sr/86 Sr isotope ratio over 0.711, and Japanese lacquer films have a ratio lower than 0.710; the borderline is around 87 Sr/86 Sr = 0.710. In order to identify the lacquer of mitsuda-e and hakue samples in this study, we also tried to analyze the 87 Sr/86 Sr isotope ratio. However, because the lacquer sap used in the mitsuda-e sample is a mixture of urushiol and laccol and laccol lacquer trees are mainly grown in Vietnam, which belongs to the Asian mainland, we predicted that its 87 Sr/86 Sr isotope ratio should more than 0.710; therefore, we measured the 87 Sr/86 Sr isotope ratio of only the hakue sample, and the results are shown in Fig. 10. Fig. 10 shows the 87 Sr/86 Sr isotope ratio results of lacquer sap tapped from lacquer trees grown in Hokkaido (HKD), Iwate
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