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86Sr isotope ratio
Journal of Analytical and Applied Pyrolysis 117 (2016) 25–29
Contents lists available at ScienceDirect
Journal of Analytical and Applied Pyrolysis journal homepage: www.elsevier.com/locate/jaap
Identification of Ryukyu lacquerwares by pyrolysis-gas chromatography/mass spectrometry and 87 Sr/86 Sr isotope ratio Takayuki Honda a , Rong Lu a,∗ , Yoshimi Kamiya b , Shun’ichi Nakai c , Tetsuo Miyakoshi a a b c
Department of Applied Chemistry, Meiji University, 1-1-1 Higashimita, Tama-ku, Kawasaki-shi 214-8571, Japan Tokyo Metropolitan Industrial Technology Research Institute, 3-6-1 Azuma-cho, Akishima-shi, Tokyo 196-0033, Japan Earthquake Research Institute, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan
a r t i c l e
i n f o
Article history: Received 13 November 2015 Received in revised form 25 December 2015 Accepted 26 December 2015 Available online 29 December 2015 Keywords: Lacquer source Lacquer species Strontium Cross-section
a b s t r a c t Six pieces of lacquer obtained from Ryukyu lacquerwares produced in the 17–19th century in the Ryukyu Kingdom were analyzed by pyrolysis gas chromatography/mass spectrometry and 87 Sr/86 Sr isotope ratio measurements to determine the identity of the lacquer source. The results were compared with the standard of natural lacquer film to discriminate lacquer species. Four pieces were made used lacquer sap collected from Toxicodendron vernicifluum lacquer tree, and other two pieces were made with lacquer sap tapped from Toxicodendron succedanea lacquer tree according to the characteristics of the pyrolysis products. All 87 Sr/86 Sr isotope values of urushiol lacquerwares are over 0.71, suggesting that the origin of lacquer trees were the Asian continent. © 2016 Elsevier B.V. All rights reserved.
1. Introduction Lacquer is a kind of special natural resin tapped from lacquer trees belongs to Toxicodendron vernicifluum, Toxicodendron succedanea, and Gluta usitata family. Because it can form a beautiful and durable film after drying, lacquer has been used to prepare crafts or wares not only for protection but also for aesthetic effect in Asian countries for more than 7000 years [1,2], and lacquer culture is still a part of modern life in Asia [3]. In order to make a better conservation and restoration of the valuable ancient lacquerwares, identification of the lacquer origin and species is important. Although solid nuclear magnetic resonance (NMR) [4] and Fourier transform infrared spectroscopy (FT-IR) [5] have been employed, several troublesome pre-treatments are required and cannot obtain clear results. On the other hand, pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) is an effective method for analyzing lacquer film and other natural resins due to the different characteristic pyrolysis products [6–11]. An improved method with direct probe-Li+ ion attachment mass spectrometry used to analyze Japanese lacquer film also was reported [12]. Previously, we analyzed six pieces [13] and two pieces [14] of Ryukyu lacquerwares belonging to the
∗ Corresponding author. E-mail address: [email protected] (R. Lu). http://dx.doi.org/10.1016/j.jaap.2015.12.021 0165-2370/© 2016 Elsevier B.V. All rights reserved.
Urasoe Art Museum by Py-GC/MS. The characteristics of the pyrolysis products of urushiol (MW = 320), 3-heptylcatechol (MW = 208), 3-heptylphenol (MW = 192), laccol (MW = 348), 3-nonylcatechol (MW = 236), and 3-nonylphenol (MW = 220) were detected, suggesting that these Ryukyu lacquerwares were coated with alone and/or mixed with each other of lacquer sap tapped from T. vernicifluum and T. succedanea lacquer trees. In this study, three pieces from lacquer boxes, two pieces from lacquer trays, and one piece from lacquer cupboard of Ryukyu lacquerwares belonging to the Urasoe Art Museum were analyzed by Py-GC/MS and 87 Sr/86 Sr isotope ratio measurements. Based on the results, Ryukyu lacquer culture and trade history are discussed. 2. Experimental The information of six pieces of lacquer that obtained from Ryukyu lacquerwares belonging to Urasoe Art Museum are summarized in Table 1, and the photos of objects are shown in Fig. 1. 2.1. 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
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T. Honda et al. / Journal of Analytical and Applied Pyrolysis 117 (2016) 25–29
Fig. 1. Photos of lacquerwares (the Nos. are the same as Table 1).
Table 1 Samples information. No.
Art name (No. in Museum)
Size (L × W × H, cm)a
Age (century)
1 2 3 4
Green wood tray with Hakue (4) Black wood box with Raden (31) Black wood box with Raden (32) Black wood lunch box with Raden (33) Black/red wood cupboard with Raden (43) Black wood tray with Raden (44)
36 × 36.4 × 4.1 11.9 × 11.9 × 9 10.3 × 10.3 × 11.3 13 × 14.3 × 18.8
16–17 17–18 17–18 18–19
46.5 × 77.6 × 131.5
17–18
15.2 × 15.2 × 4.5
17–18
5
6 a
L: length; W: width; H: height.
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 320 ◦ C, and then hold for
10 min at 320 ◦ 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).
2.2.
87 Sr/86 Sr
isotope ratio measurement
The 87 Sr/86 Sr isotope ratio measurement is carried out as the same as our previous report [15] and the detail of method is described as follow.
2.2.1. (1) 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.
Table 2 Pyrolysis products of Ryukyu lacquer films and their species. No.
Lacquer species
1 2 3 4 5 6
T. succedanea T. vernicifluum T. succedanea T. vernicifluum T. vernicifluum T. vernicifluum
Pyrolysis products Monomer
Alkylcatechol
Alkylphenol
Drying oil
Laccol Urushiol Laccol Urushiol Urushiol Urushiol
3-Nonylcatechol 3-Heptylcatechol 3-Nonylcatechol 3-Heptylcatechol 3-Heptylcatechol 3-Heptylcatechol
3-Nonylphenol 3-Heptylphenol 3-Nonylphenol 3-Heptylphenol 3-Heptylphenol 3-Heptylphenol
Fatty acids Fatty acids Fatty acids Fatty acids Fatty acids Fatty acids
T. Honda et al. / Journal of Analytical and Applied Pyrolysis 117 (2016) 25–29
27
Fig. 2. Py-GC/MS chromatogram at m/z = 108 of sample No. 4.
Fig. 3. Py-GC/MS chromatogram at m/z = 108 of sample No. 3.
Strontium 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 strontium 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 strontium; this was called sample II. 2.2.2. (2) Inductively-coupled plasma mass spectrometry Sample II was analyzed by isoprobe multicollector inductivelycoupled 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 mea-
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T. Honda et al. / Journal of Analytical and Applied Pyrolysis 117 (2016) 25–29
Fig. 4. Py-GC/MS chromatogram at m/z = 60 of sample No. 5.
sured. 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). 3. Results and discussion 3.1. Pyrolysis GC–MS analysis All pieces of Ryukyu lacquerwares in Table 1 were analyzed by Py-GC/MS at 500 ◦ C. Fig. 2 shows the mass chromatograms at m/z = 108 of sample No. 4 and standard lacquers. Compared with the standard lacquers, it can be found that the coating material of sample No. 4 is the lacquer collected from T. vernicifluum lacquer tree because both of 3-heptylphenol (C7) and 3-pentadecylphenol (C15) were detected. Samples No. 2, 5, and 6 showed the similar mass chromatogram and mass spectra to the sample No. 4, suggesting that these four lacquerwares were made from T. vernicifluum. Fig. 3 shows the mass chromatograms at m/z = 108 of sample No. 3 and standard lacquers. It can be concluded that the coating material of sample 3 is the lacquer collected from T. succedanea lacquer tree due to the characteristics of the pyrolysis products of 3-nonylphenol (C9) and 3-heptadecylphenol (C17) were detected compared with the standard lacquers. Samples No. 1 also showed the similar mass chromatogram and mass spectra to the sample No. 3, implying that these two lacquerwares were made from T. succedanea. Because a drying oil is usually used to increase the luster and elasticity of the lacquer film in Asian lacquer technology, the m/z = 60 chromatogram of all six samples by pyrolysis GC–MS were analyzed [16]. Fig. 4 shows the mass chromatograms at m/z = 60 of sample No. 5. The peaks at retention time of 18.672 min (C16) and 20.022 min (C18) are fatty acid that considered due to palmitic acid (C16) and stearic acid (C18) oils were detected. Because all six samples showed almost the same mass chromatograms at m/z = 60, it can be concluded that all these six samples mixed with drying oils during the lacquer-coating process. The pyrolysis products of the six samples are summarized in Table 2.
Fig. 5. Strontium isotope ratios of Japanese (䊏), Chinese ( lacquers.
), and Ryukyu ()
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 six lacquer samples in this study, we also tried to analyze the 87 Sr/86 Sr isotope ratio. However, because the samples No. 1 and No. 3 are 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 urushiol sample, and the results are shown in Fig. 5. Fig. 5 shows the 87 Sr/86 Sr isotope ratio results of lacquer sap tapped from lacquer trees grown in Hokkaido (HKD), Iwate 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 four Ryukyu samples in this study (). 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. All the 87 Sr/86 Sr isotope ratio of the four Ryukyu samples is higher than 0.710, suggesting that these four Ryukyu lacquerwares are made of lacquer sap tapped from a lacquer tree grown in the Chinese mainland. It has been believed that Japanese lacquer tree and lacquer technology from Chinese mainland through the Korean Peninsula because lacquer originated in China. Ryukyu was an independent kingdom in its long history till to 19th century, and had much trade with the surrounding countries, especially China. This result also demonstrates the prosperous trade of the Ryukyu Kingdom. 4. Conclusion The analysis results of six Ryukyu lacquer pieces showed that four pieces were coating with the lacquer collected from T. vernicifluum and two pieces with the lacquer collected from T. succedanea lacquer trees grown on the Asian continent. Ryukyu was an independent kingdom in its long history and traded very actively with surrounding countries. The analysis results of this study confirmed that Ryukyu people efficiently used the imported lacquer from Vietnam and China to make lacquerwares.
3.2. Sr isotopes ratio Acknowledgements Because the ancient Chinese mainland Strontium isotope ratio is higher than that contained in the relatively young Japanese islands, the ratio has been used to identify the provenance of green onions in Japan [17]. 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
The authors thank Masako Miyazato of the Urasoe Art Museum, Okinawa, Japan, for donating of the Ryukyu ancient lacquer films. This work was financially supported by the Japan Society for the Promotion of Science (JSPS) Grant Numbers 25282076 and 26282070, and in part by a Grant-in-Aid for Scientific Research on
T. Honda et al. / Journal of Analytical and Applied Pyrolysis 117 (2016) 25–29
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. Terada, K. Oda, H. Oyabu, T. Asami, Lacquer—The Science and Practice, Rikou Publisher, Tokyo, Japan, 1999. [2] T. Miyakoshi, K. Nagase, T. Yoshida, Progress of Lacquer Chemistry, IPC Publisher, Tokyo, Japan, 1999. [3] R. Lu, T. Yoshida, T. Miyakoshi, Oriental lacquer: a natural polymer, Polym. Rev. 53 (2013) 153–191. [4] J. Lambert, J. Frye, G. Carriveau, The structure of oriental lacquer by solid state nuclear magnetic resonance spectroscopy, Archaeometry 33 (1991) 87–93. [5] J. Kumanotani, Super-durable structure of oriental lacquer films, Polym. Mater. 59 (1988) 278–283. [6] G. Chiavari, R. Mazzeo, Characterisation of paint layers in Chinese archaeological relics by pyrolysis-GC–MS, Chromatographia 49 (1999) 268–272. [7] L. He, M. Nie, G. Chiavari, R. Mazzeo, Analytical characterization of binding mediu used in ancient Chinese artworks by pyrolysis-gas chromatography/mass spectrometry, Microchem. J. 85 (2007) 347–353. [8] J.C. Frade, M.I. Ribeiro, J. Graca, J. Rodrigues, Applying pyrolysis-gas chromatography/mass spectrometry to the identification of oriental lacquers: study of two lacquered shields, Anal. Bioanal. Chem. 395 (2009) 2167–2174. [9] S.-Y. Wei, V. Pintus, V. Pitthard, M. Schreiner, G.-D. Song, Analytical characterization of lacquer objects excavated from a Chu tomb in China, J. Archaeol. Sci. 38 (2011) 2667–2674.
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[10] S. Saverwyns, M. Vermeulen, E. Binnebeke, Preliminary investigation of the chemical composition of European lacquers using pyrolysis gas chromatography–mass spectrometry, e-Preserv. Sci. 11 (2014) 64–75. [11] D. Tamburini, I. Bonaduce, M.P. Colombini, Characterization and identification of urushi using in situ pyrolysis/silylation-gas chromatography–mass spectrometry, J. Anal. Appl. Pyrolysis 111 (2015) 33–140. [12] M. Tsukagoshi, Y. Kitahara, S. Takahashi, T. Fujii, Pyrolysis analysis of Japanese lacquer film: direct probe-Li+ ion attachment mass spectrometry versus pyrolysis/gas chromatography/mass spectrometry, J. Anal. Appl. Pyrolysis 95 (2012) 156–163. [13] R. Lu, X.-M. Ma, Y. Kamiya, T. Honda, Y. Kamiya, A. Okamoto, T. Miyakoshi, Identification of Ryukyu lacquerwares by pyrolysis-gas chromatography/mass spectrometry, J. Anal. Appl. Pyrolysis 80 (2007) 101–110. [14] T. Honda, R. Lu, M. Yamabuki, D. Ando, M. Miyazato, K. Yoshida, T. Miyakoshi, Investigation of Ryukyu lacquerwares by pyrolysis-gas chromatography/mass spectrometry, J. Anal. Appl. Pyrolysis 113 (2015) 41–45. [15] R. Lu, T. Honda, M. Sato, K. Yoshida, T. Miyakoshi, Determination of provenance and species of Japanese Jomon lacquer by pyrolysis-gas chromatography/mass spectrometry and 87 Sr/86 Sr isotope ratio, J. Anal. Appl. Pyrolysis 113 (2015) 84–88. [16] R. Lu, Y. Kamiya, T. Miyakoshi, Applied analysis of lacquer films based on pyrolysis-gas chromatography/mass spectrometry, Talanta 70 (2006) 370–376. [17] 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.
Contents lists available at ScienceDirect
Journal of Analytical and Applied Pyrolysis journal homepage: www.elsevier.com/locate/jaap
Identification of Ryukyu lacquerwares by pyrolysis-gas chromatography/mass spectrometry and 87 Sr/86 Sr isotope ratio Takayuki Honda a , Rong Lu a,∗ , Yoshimi Kamiya b , Shun’ichi Nakai c , Tetsuo Miyakoshi a a b c
Department of Applied Chemistry, Meiji University, 1-1-1 Higashimita, Tama-ku, Kawasaki-shi 214-8571, Japan Tokyo Metropolitan Industrial Technology Research Institute, 3-6-1 Azuma-cho, Akishima-shi, Tokyo 196-0033, Japan Earthquake Research Institute, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan
a r t i c l e
i n f o
Article history: Received 13 November 2015 Received in revised form 25 December 2015 Accepted 26 December 2015 Available online 29 December 2015 Keywords: Lacquer source Lacquer species Strontium Cross-section
a b s t r a c t Six pieces of lacquer obtained from Ryukyu lacquerwares produced in the 17–19th century in the Ryukyu Kingdom were analyzed by pyrolysis gas chromatography/mass spectrometry and 87 Sr/86 Sr isotope ratio measurements to determine the identity of the lacquer source. The results were compared with the standard of natural lacquer film to discriminate lacquer species. Four pieces were made used lacquer sap collected from Toxicodendron vernicifluum lacquer tree, and other two pieces were made with lacquer sap tapped from Toxicodendron succedanea lacquer tree according to the characteristics of the pyrolysis products. All 87 Sr/86 Sr isotope values of urushiol lacquerwares are over 0.71, suggesting that the origin of lacquer trees were the Asian continent. © 2016 Elsevier B.V. All rights reserved.
1. Introduction Lacquer is a kind of special natural resin tapped from lacquer trees belongs to Toxicodendron vernicifluum, Toxicodendron succedanea, and Gluta usitata family. Because it can form a beautiful and durable film after drying, lacquer has been used to prepare crafts or wares not only for protection but also for aesthetic effect in Asian countries for more than 7000 years [1,2], and lacquer culture is still a part of modern life in Asia [3]. In order to make a better conservation and restoration of the valuable ancient lacquerwares, identification of the lacquer origin and species is important. Although solid nuclear magnetic resonance (NMR) [4] and Fourier transform infrared spectroscopy (FT-IR) [5] have been employed, several troublesome pre-treatments are required and cannot obtain clear results. On the other hand, pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) is an effective method for analyzing lacquer film and other natural resins due to the different characteristic pyrolysis products [6–11]. An improved method with direct probe-Li+ ion attachment mass spectrometry used to analyze Japanese lacquer film also was reported [12]. Previously, we analyzed six pieces [13] and two pieces [14] of Ryukyu lacquerwares belonging to the
∗ Corresponding author. E-mail address: [email protected] (R. Lu). http://dx.doi.org/10.1016/j.jaap.2015.12.021 0165-2370/© 2016 Elsevier B.V. All rights reserved.
Urasoe Art Museum by Py-GC/MS. The characteristics of the pyrolysis products of urushiol (MW = 320), 3-heptylcatechol (MW = 208), 3-heptylphenol (MW = 192), laccol (MW = 348), 3-nonylcatechol (MW = 236), and 3-nonylphenol (MW = 220) were detected, suggesting that these Ryukyu lacquerwares were coated with alone and/or mixed with each other of lacquer sap tapped from T. vernicifluum and T. succedanea lacquer trees. In this study, three pieces from lacquer boxes, two pieces from lacquer trays, and one piece from lacquer cupboard of Ryukyu lacquerwares belonging to the Urasoe Art Museum were analyzed by Py-GC/MS and 87 Sr/86 Sr isotope ratio measurements. Based on the results, Ryukyu lacquer culture and trade history are discussed. 2. Experimental The information of six pieces of lacquer that obtained from Ryukyu lacquerwares belonging to Urasoe Art Museum are summarized in Table 1, and the photos of objects are shown in Fig. 1. 2.1. 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
26
T. Honda et al. / Journal of Analytical and Applied Pyrolysis 117 (2016) 25–29
Fig. 1. Photos of lacquerwares (the Nos. are the same as Table 1).
Table 1 Samples information. No.
Art name (No. in Museum)
Size (L × W × H, cm)a
Age (century)
1 2 3 4
Green wood tray with Hakue (4) Black wood box with Raden (31) Black wood box with Raden (32) Black wood lunch box with Raden (33) Black/red wood cupboard with Raden (43) Black wood tray with Raden (44)
36 × 36.4 × 4.1 11.9 × 11.9 × 9 10.3 × 10.3 × 11.3 13 × 14.3 × 18.8
16–17 17–18 17–18 18–19
46.5 × 77.6 × 131.5
17–18
15.2 × 15.2 × 4.5
17–18
5
6 a
L: length; W: width; H: height.
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 320 ◦ C, and then hold for
10 min at 320 ◦ 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).
2.2.
87 Sr/86 Sr
isotope ratio measurement
The 87 Sr/86 Sr isotope ratio measurement is carried out as the same as our previous report [15] and the detail of method is described as follow.
2.2.1. (1) 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.
Table 2 Pyrolysis products of Ryukyu lacquer films and their species. No.
Lacquer species
1 2 3 4 5 6
T. succedanea T. vernicifluum T. succedanea T. vernicifluum T. vernicifluum T. vernicifluum
Pyrolysis products Monomer
Alkylcatechol
Alkylphenol
Drying oil
Laccol Urushiol Laccol Urushiol Urushiol Urushiol
3-Nonylcatechol 3-Heptylcatechol 3-Nonylcatechol 3-Heptylcatechol 3-Heptylcatechol 3-Heptylcatechol
3-Nonylphenol 3-Heptylphenol 3-Nonylphenol 3-Heptylphenol 3-Heptylphenol 3-Heptylphenol
Fatty acids Fatty acids Fatty acids Fatty acids Fatty acids Fatty acids
T. Honda et al. / Journal of Analytical and Applied Pyrolysis 117 (2016) 25–29
27
Fig. 2. Py-GC/MS chromatogram at m/z = 108 of sample No. 4.
Fig. 3. Py-GC/MS chromatogram at m/z = 108 of sample No. 3.
Strontium 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 strontium 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 strontium; this was called sample II. 2.2.2. (2) Inductively-coupled plasma mass spectrometry Sample II was analyzed by isoprobe multicollector inductivelycoupled 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 mea-
28
T. Honda et al. / Journal of Analytical and Applied Pyrolysis 117 (2016) 25–29
Fig. 4. Py-GC/MS chromatogram at m/z = 60 of sample No. 5.
sured. 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). 3. Results and discussion 3.1. Pyrolysis GC–MS analysis All pieces of Ryukyu lacquerwares in Table 1 were analyzed by Py-GC/MS at 500 ◦ C. Fig. 2 shows the mass chromatograms at m/z = 108 of sample No. 4 and standard lacquers. Compared with the standard lacquers, it can be found that the coating material of sample No. 4 is the lacquer collected from T. vernicifluum lacquer tree because both of 3-heptylphenol (C7) and 3-pentadecylphenol (C15) were detected. Samples No. 2, 5, and 6 showed the similar mass chromatogram and mass spectra to the sample No. 4, suggesting that these four lacquerwares were made from T. vernicifluum. Fig. 3 shows the mass chromatograms at m/z = 108 of sample No. 3 and standard lacquers. It can be concluded that the coating material of sample 3 is the lacquer collected from T. succedanea lacquer tree due to the characteristics of the pyrolysis products of 3-nonylphenol (C9) and 3-heptadecylphenol (C17) were detected compared with the standard lacquers. Samples No. 1 also showed the similar mass chromatogram and mass spectra to the sample No. 3, implying that these two lacquerwares were made from T. succedanea. Because a drying oil is usually used to increase the luster and elasticity of the lacquer film in Asian lacquer technology, the m/z = 60 chromatogram of all six samples by pyrolysis GC–MS were analyzed [16]. Fig. 4 shows the mass chromatograms at m/z = 60 of sample No. 5. The peaks at retention time of 18.672 min (C16) and 20.022 min (C18) are fatty acid that considered due to palmitic acid (C16) and stearic acid (C18) oils were detected. Because all six samples showed almost the same mass chromatograms at m/z = 60, it can be concluded that all these six samples mixed with drying oils during the lacquer-coating process. The pyrolysis products of the six samples are summarized in Table 2.
Fig. 5. Strontium isotope ratios of Japanese (䊏), Chinese ( lacquers.
), and Ryukyu ()
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 six lacquer samples in this study, we also tried to analyze the 87 Sr/86 Sr isotope ratio. However, because the samples No. 1 and No. 3 are 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 urushiol sample, and the results are shown in Fig. 5. Fig. 5 shows the 87 Sr/86 Sr isotope ratio results of lacquer sap tapped from lacquer trees grown in Hokkaido (HKD), Iwate 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 four Ryukyu samples in this study (). 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. All the 87 Sr/86 Sr isotope ratio of the four Ryukyu samples is higher than 0.710, suggesting that these four Ryukyu lacquerwares are made of lacquer sap tapped from a lacquer tree grown in the Chinese mainland. It has been believed that Japanese lacquer tree and lacquer technology from Chinese mainland through the Korean Peninsula because lacquer originated in China. Ryukyu was an independent kingdom in its long history till to 19th century, and had much trade with the surrounding countries, especially China. This result also demonstrates the prosperous trade of the Ryukyu Kingdom. 4. Conclusion The analysis results of six Ryukyu lacquer pieces showed that four pieces were coating with the lacquer collected from T. vernicifluum and two pieces with the lacquer collected from T. succedanea lacquer trees grown on the Asian continent. Ryukyu was an independent kingdom in its long history and traded very actively with surrounding countries. The analysis results of this study confirmed that Ryukyu people efficiently used the imported lacquer from Vietnam and China to make lacquerwares.
3.2. Sr isotopes ratio Acknowledgements Because the ancient Chinese mainland Strontium isotope ratio is higher than that contained in the relatively young Japanese islands, the ratio has been used to identify the provenance of green onions in Japan [17]. 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
The authors thank Masako Miyazato of the Urasoe Art Museum, Okinawa, Japan, for donating of the Ryukyu ancient lacquer films. This work was financially supported by the Japan Society for the Promotion of Science (JSPS) Grant Numbers 25282076 and 26282070, and in part by a Grant-in-Aid for Scientific Research on
T. Honda et al. / Journal of Analytical and Applied Pyrolysis 117 (2016) 25–29
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