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Dye Analysis of Shosoin Textiles Using Excitation-Emission Matrix Fluorescence and Ultraviolet-Visible Reflectance Spectroscopic Techniques Rikiya Nakamura,* Yoko Tanaka, Atsuhiko Ogata, and Masakazu Naruse Office of the Shosoin Treasure House, Imperial Household Agency, Nara, Japan The dyes of 8th century textiles, treasured for more than 1250 years in the Shosoin treasure repository in Japan, were analyzed by nondestructive methods, i.e., excitationemission matrix (EEM) fluorescence and ultraviolet-visible (UV-vis) reflectance spectrometry, in combination with natural dye references extracted from plants, which have been widely used from ancient times. In this analysis, five dyes were found in the following objects: embroidered shoes dedicated to Great Buddha of the Todaiji temple by the empress of that time, the cloth lining for a case holding a mirror belonging to the emperor of that time, two rolls of yellow and light green plain-weave silks, and a sleeveless coat used for a musical in a Buddhist ceremony in 752 A.D. EEM fluorescence spectrometry distinguished kihada yellow (Amur cork tree), kariyasu yellow (eulalia), and akane red (Japanese madder). UV-vis spectrometry also distinguished kariyasu yellow, ai blue (knotweed), akane red, and shikon purple (murasaki); the characteristic peaks of these dyes were detected by a second derivatization. The results show that although the dyes used easily degrade with age, EEM fluorescence and UV-vis reflectance spectrometry are useful for distinguishing dyes used in the Shosoin textiles, which had been stored for more than 1250 years. Shosoin is a famous repository at the Todaiji temple constructed by the Emperor Shomu (701-756 A.D.) in Nara, Japan, in the mid-8th century; it stores about 9 000 valuable objects collectively known as the “Shosoin Treasures” at the present day. Almost all the treasures date from the 8th century; access is strictly prohibited by any person for any purpose, except for the annual 2 week exhibition, because of the importance of the objects to Japanese history. The Shosoin treasures include textiles, ancient documents, drugs, and various beautiful artifacts such as musical instruments, mirrors, interior decorations, stationery, masks, and Buddhist altar fittings. Shosoin textiles involving clothes, accessories, furnishing, bags, banners, cloth linings for boxes, etc. represent the about 5 000 treasure collection; these textiles have enchanted many Japanese people with the variety of beautiful colors made from natural dyes. The analysis of dyes used in Shosoin textiles * To whom correspondence should be addressed. E-mail: ssi25b@ kunaicho.go.jp. 10.1021/ac900428a CCC: $40.75 2009 American Chemical Society Published on Web 06/09/2009
provides valuable information about the history of textile crafts in the 8th century not only in ancient Japan but also East Asia, since some of the treasure objects were passed from China and Korea to Japan. The information is also very important to devise strategies for the conservation and repair of the Shosoin textiles. There are a variety of analytical methods for natural dyes: thin-layer chromatography (TLC), high-performance liquid chromatography (HPLC), capillary electrophoresis (CE), various spectrometry techniques such as fluorescence, ultravioletvisible (UV-vis), Raman, and so on.1-16 HPLC is widely used for analyzing dyes used in art objects.1,4-12 However, HPLC for dye analysis requires taking samples from the important objects, which is not ideal due to the damage to the objects. In contrast, the fluorescence and UV-vis reflectance spectroscopic methods are very attractive because they are nondestructive and do not require taking samples. Previous reports have shown that excitation-emission matrix (EEM) fluorescence spectrometry allows for the distinction of natural yellow, red, and indigo (1) Hofenk de Graaf, J. H. The Colorful Past: Origins, Chemistry and Identification of Natural Dyestuff; Archetype Publications: London, 2004. (2) Cardon, D. Natural Dyes: Sources, Tradition, Technology and Science; Archetype Publications: London, 2007. (3) Schweppe, H. In Historic Textile and Materials; Needles, H. J., Zeronian, S. H., Eds.; Advances in Chemistry Series 212; American Chemical Society: Washington, DC, 1986; Chapter 8. (4) Wouters, J. Stud. Conserv. 1985, 30, 119–128. (5) Wouters, J.; Maes, L.; Germer, R. Stud. Conserv. 1990, 35, 89–92. (6) Zhang, X.; Boytner, R.; Cabrera, J. L.; Lausen, L. Anal. Chem. 2007, 79, 1575–1582. (7) Gibbs, P. J.; Seddon, K. R; Brovenko, N. M.; Petrosyan, Y. A.; Barnard, M. Anal. Chem. 1997, 69, 1965–1969. (8) Orska-Gawrys´, J.; Surowiec, I.; Kehn, J.; Rejniak, H.; Urbaniak-Walczak, K.; Trojanowicz, M. J. Chromatogr., A 2003, 989, 239–248. (9) Szostek, B.; Orska-Gawrys, J.; Sourowiec, I.; Trojanowicz, M. J. Chromatogr., A 2003, 1012, 179–192. (10) Novotna´, P.; Paca´kova´, V.; Bosa´kova´, Z.; Sˇtulı´k, K. J. Chromatogr., A 1999, 863, 235–241. (11) Shibayama, N.; Yamaoka, R.; Sato, M.; Iida, J. J. Mass Spectrom. Jpn. 1989, 39, 123–131. (12) Saito, M.H; Hayashi, A.; Kojima, M. Dyes History Archaeol. 2003, 19, 79– 87. (13) Miyoshi, T.; Matsuda, Y. Jpn. J. Appl. Phys. 1987, 26, 239–245. (14) Clementi, C.; Nowik, W.; Romani, A.; Cibin, F.; Favaro, G. Anal. Chim. Acta 2007, 596, 46–54. (15) Schrader, B.; Schulz, H.; Andreev, G. N.; Klump, H. H.; Sawatzki, J. Talanta 2000, 53, 35–45. (16) Chen, K.; Von-Dinh, K.-C.; Yan, F.; Wabuyele, M. B.; Vo-Dinh, T. Anal. Chim. Acta 2006, 569, 234–237.
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Figure 1. Shosoin textiles analyzed in this study: (a) the embroidered shoes, (b) the toe section of the embroidered shoes with the analyzed points marked by an arrow, (c) the observed cloth lining for the mirror case, (d) the red twill of the cloth lining for the mirror case, (e) the reverse of the cloth lining for the mirror case, (f) the light green twill of the cloth lining for a mirror case, (g, h) the roll of yellow plain weave silk, (i, j) the roll of light green plain weave silk, (k) the sleeveless coat for a dancer, (l) the red plain silk of the sleeveless coat, and (m) the purple plain silk of the sleeveless coat.
dyes used in art objects.17,18 EEM fluorescence spectroscopy measures the emission spectra over a wide range of excitation wavelengths, resulting in a fluorescent intensity landscape defined by the excitation and emission wavelength range. The application of UV-vis reflectance spectrometry has been reported to be useful for the distinction of several kinds of red dyes and indigo dye in art objects.19 However, there have been almost no reports on the applicability of these spectroscopic techniques to important historical textiles more than 1250 years old.20 This article reports on the analysis of dyes used in the Shosoin textiles by EEM fluorescence and UV-vis reflectance (17) (18) (19) (20)
Shimoyama, S.; Noda, Y. Dyes History Archaeol. 1993, 12, 45–56. Shimoyama, S.; Noda, Y. Dyes History Archaeol. 1994, 13, 14–26. Leona, M.; Winter, J. Stud. Conserv. 2001, 46, 153–162. Matsuda, Y. Buakazai Hozon-Syufuku Gakkaisi (Sci. Conserv. Jpn.) 1997, 41, 54–63.
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spectrometry. Authentic Shosoin textiles have not been analyzed for the distinction of dyes through analytical methods, except for the paper chromatogram, until now.21,22 EEM fluorescence reflectance spectrometry was performed using an instrument equipped with an optical fiber as a nondestructive method. UV-vis reflectance spectrometry was conducted using an instrument coupled with an integrating sphere. In UV-vis spectrometry, the second-derivative spectrum was used to distinguish the dyes. Here, we discuss not only the availability of EEM fluorescence and UV-vis reflectance spectrometry for the distinction of five dyes, kihada yellow, kariyasu yellow, ai blue, akane red, and shikon purple, but also the limitation of these analyses for each dye used in the Shosoin textiles. (21) Uemura, R.; Takagi, Y. Shoryobu-kiyo (Bull. Off. Arch. Imperial Household Agency) 1959, 11, 72–76.
Table 1. Shosoin Textiles Analyzed in This Study warp analyzed part
textiles
color
weave
embroidered shoes
toe
yellow
cloth lining for the mirror case cloth lining for the mirror case roll of yellow plain weave silk roll of light green plain weave silk sleeveless coat for a dancer
backside
light green twill
sleeveless coat for a dancer a
embroidery
weft
EEM
0.33
353/526 441/529 353/528 441/529 371/607
19 20 25 27 86
30
0.28
371/514
28
0.25
28
0.30
34
0.25
31
0.32
371/514 441/525 371/608
55 51 38
69
0.15
56
0.1
b
b
a
a
a
a
51
0.17
24
0.35
twill
46
0.15
38
plain
46
0.23
light green plain
40
inside
red
plain
body
purple
plain
outer side red yellow
UV-vis
peak tops relative density diameter, density, diameter, (λex/λem, intensity for (cm-1) (mm) (cm-1) (mm) nm/nm) reference (%)
peak tops (λmax, nm) a 470 470, 505, 550 (shoulder) 465 460, 680 470, 505, 550 (shoulder) 550, 605
b
Not measured. Not observed for characteristic peaks.
MATERIALS AND METHODS Shosoin Textiles Analyzed in This Study. The Shosoin textiles analyzed are as follows: a pair of embroidered shoes formerly belonging to a empress (Figure 1a,b), the cloth lining of an octagonal mirror case (Figure 1c-f), a roll of yellow plain silk (Figure 1g,h), a roll of light green plain silk (Figure 1i,j), and a sleeveless coat for a dancer (Figure 1k-m). All of the textiles date back from the 8th century A.D. The characters of the textiles are summarized in Table 1. The shoes and the cloth lining of the octagonal mirror case were dedicated to Great Buddha of the Todaiji temple in 756 A.D. by the Empress Komyo (701-760 A.D.). The yellow threads of the embroidered toe parts were analyzed in this study (Figure 1b). The cloth lining of the octagonal mirror case belonged to used to be the property of the Emperor Shomu; it consists of red twill silk with an eight-lobed flower pattern for the outside and light green twill silk with a quadruple lozenge pattern for the backside (Figure 1d,f). The red and light green twills were analyzed for this study. The roll of yellow plain silk was a payment of tax from Suruga (the present Shizuoka prefecture), Japan, in 753 A.D.; this is indicated from the inscription. The roll of light green silk was also a tax payment. The sleeveless coat was used by a dancer in the ancient To-sangaku musical performed for a large Buddhist opening ceremony at the Todaiji temple in 752 A.D. The outer torso section and the inside are plain purple and bright red silks respectively. The purple and red silks were analyzed for this study (Figure 1l,m). The measurements of the shoes and two rolls of plain silk were directly conducted for dye analysis. The analyses of the twill cloth lining and sleeveless coat were performed using fragments not returned to their original places during their repair. Materials for Dye Reference. The distinctions of the dyes used in the Shosoin textiles by EEM fluorescence and UV-vis spectrometry were demonstrated with silks dyed with the following natural dyes: kihada (Amur cork tree; Phellodendron amurense) yellow, kariyasu (eulalia; Miscanthus tinctorius) yellow, akane (Japanese madder; Rubia akane) red, shikon (murasaki; Lithospermum erythrorhizon) purple, and ai (knotweed; Persicaria tinctoria) blue. All dye references prepared were found in the (22) Takagi, Y. Shoryobu-kiyo (Bull. Off. Arch. Imperial Household Agency) 1970, 21, 48–74.
Shosoin documents describing the 8th century or an ancient law document, Engishiki, edited in 967 A.D. The bark of kihada, stems and leaves of kariyasu, roots of shikon, and silk fabrics were purchased from TanakaNao Co. (Kyoto, Japan). The roots of akane used in this study were a native of Japan. These materials were washed well under running water before usage. The ai pigment that floated on the dyeing bath of knotweed was collected. Preparation of Dyeing Bath and Lye. Kihada, kariyasu, and akane dyes were extracted in water (150 mL) for 15 min at 80 °C from the bark of kihada (4.4 g), stems and leaves of the kariyasu (6.0 g), and roots of the akane (3.0 g), respectively. The extraction of kihada and akane was carried out twice. The two solutions from the extractions for each dye were combined. The extract (6.0 mL) was diluted with water (160 mL) for dyeing. Because of concern for akane, the pH of the bath was adjusted to 4. Extraction from the shikon plant was carried out by soaking 18 g of the roots of murasaki in 140 mL of 1.5% aqueous acetic acid for 3 h at room temperature. The extract was used for the dyeing bath for shikon purple. The dyeing bath of ai was prepared by the reduction of ai pigment (82 mg) using sodium dithionate (0.81 g) and sodium carbonate (0.82 g) in 150 mL of water at room temperature. The reduction of ai pigment using sodium dithionate and sodium carbonate was carried out as a substitute for the formation of indigo by an enzyme of Bacillus alkaliphilus in ancient Japan. The lye of camellia ash was prepared by extractions of 43 g of the ash in 0.88 L of water for 15 min at 85 °C. Preparation of the lye derived from Quercus sp. was performed by the addition of water (140 mL; 80 °C) to 44 g of the ash of leaves and stems of Quercus sp. Water decreased through the preparation of the lye was made up to 140 mL. Dyeing of Silks. For the dyeing of kihada yellow, silk (2.0 g) was soaked in the bath of kihada (140 mL) for 15 min at 80 °C. Undiluted extract from the kihada plant (5.0 mL) was added to the bath every 15 min during the dyeing. The addition was performed three times for adjusting the color hue. The kihada yellow reference was prepared with no mordant. For the preparation of the kariyasu yellow reference, silk (2.0 g) was soaked in 44 mL of the dyeing bath for kariyasu yellow for 15 min at 80 °C. The dyed silk was left in the lye of camellia ash (40 mL) at room temperature for 20 min. The mordanted silk was rinsed with running water. The kariyasu reference followed by ai blue was Analytical Chemistry, Vol. 81, No. 14, July 15, 2009
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Table 2. EEM and UV-Visible Data of Dye References in This Studya
a Silk dyed with each natural dyes. b Excitation and emission wavelength range measured at λex ) 300-600 nm and λem ) 300-700 nm. c Dyed with only kariyasu yellow. d Dyed with kariyasu yellow with ai blue. e Not observed for the characteristic peaks. f Wavelength range measured from 190 to 900 nm.
Figure 2. EEM spectra with a λex of 300-600 nm and λem of 300-700 nm for the following: (a) the silk dyed with kihada yellow (reference), (b) the yellow threads on the toe part of the embroidered shoes, and (c) the light green twill of the cloth lining for the mirror case.
prepared by soaking the silk dyed with kariyasu yellow in the dyeing bath of ai blue (50 mL) for 1 min at room temperature. For the oxidation to indigo, the dyed silk was left in the air for 5 min. For the preparation of the akane red reference, silk (0.50 g) was left in the camellia ash (10 mL) for 20 min at room temperature before dyeing. After the pretreated silk was rinsed, 5694
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the dyeing was conducted by soaking the silk in dyeing bath for akane red (46 mL) for 15 min at 80 °C. These processes were performed three times. The dyeing of shikon purple was carried out in 140 mL of the bath for 15 min at 60 °C five times; silk (1.2 g) left in the lye of the ash of Quercus sp. (140 mL) for 20 min at room temperature was used. The mordant by lye was performed
Figure 3. Second-derivative UV-vis spectra of the (a) the silk dyed with kihada yellow (reference) and (b) light green twill of the cloth lining for the mirror case. Scheme 1. Dyeing Mechanism for Kariyasu Yellow on Silk Mordanted by Lye and Potassium Alum
for each dyeing process. The ai blue reference was prepared by soaking silk (0.25 g) in the bath (50 mL) for 5 min at room temperature and left in air for 5 min. The process was performed three times. Instruments. EEMs were obtained using a FluoroMax-3 spectrometer (Horiba Jobin Yvon) equipped with a xenon flash lamp. The sample beam was directed from a cuvette in the sample compartment to the end of a fiber optics cable. The fiber optics probe was a fiber reflectance probe from Horiba Jobin Ybon. The flat-tip probe was a bifurcated bundle of filaments mingling together at the front end. The fibers were mounted in a sheath with 4.0 mm diameter. The excitation and emission slit widths were 5.0 and 3.0 nm, respectively. EEMs were recorded in the ranges of λex ) 300-600 nm for every 17.6 nm and λex ) 300-700 nm for every 1.0 nm. The scan rate was 10 nm s-1. Data were processed with DataMax software (version 2.20), and contour EEM plots were constructed from the DataMax statistics toolbox. The UV-vis reflectance spectrometry was performed using the Shimazu UV2200A instrument equipped with W/D2 lamps. The sample beam was directed to the sample compartment equipped with an integral sphere. The slit width was 2.0 nm. The optical measurement was conducted using double beams with a plate of barium sulfate used as a reference.
Figure 4. EEM spectra with a λex of 300-600 nm and λem of 300-700 nm for the following: (a) the silk dyed with kariyasu yellow (reference) exposed to sunlight for 90 h, (b) the roll of yellow plain weave silk, (c) the silk dyed with kariyasu yellow following dyeing with ai blue (reference), and (d) the roll of light green plain weave silk.
The spectrum was recorded in reflectance mode in the range 190-900 nm. The scan rate was 16 nm s-1. The second derivatization for the UV-vis spectrum was conducted at 25 points. RESULTS AND DISCUSSION Dyes in Ancient Japan. The dye references were prepared based on the knowledge about the specific natural materials known from the Japanese historic sources, i.e., Shosoin documents and Engishiki. Shosoin documents denoted the following red, blue, and purple dyes: akane, benibana (safflower; Carthamus tinctarius), and suo (sappanwood; Caesalpinia sappan) red, ai blue, and shikon purple, respectively. Because of concern for the yellow dye, kihada yellow was only mentioned as a material for dyeing Analytical Chemistry, Vol. 81, No. 14, July 15, 2009
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Figure 5. Second-derivative UV-vis spectra of the following: (a) the silk dyed with kariyasu yellow (reference) exposed to sunlight for 90 h, (b) the roll of yellow plain weave silk, (c) the silk dyed with kariyasu yellow following dyeing with ai blue (reference), and (d) the roll of light green plain weave silk.
Figure 6. Second-derivative UV-vis spectra of (a) the silk dyed with ai blue (reference) and (b) the roll of light green plain weave silk.
paper of sutra. In Engishiki, yellow, red, blue, and purple dyes are as follows: kihada, kariyasu, and kuchinashi (cape jasmine; Gardenia augusta) yellow, akane, benibana, and suo red, ai blue, and shikon purple. Green dyes are not found in these sources; green hue was represented by using yellow dye with ai blue in ancient Japan. Comparison of EEM spectra using the silk references shows that the yellow and red dyes mentioned above are distinguishable (see Supporting Information). Second-derivative UV-vis spectrometry also distinguishes these dyes including ai blue and shikon purple. Kihada Yellow. Kihada yellow is extracted from the bark of the Amur cork tree and involves berberine as a main yellow dye molecule (Table 2).23 The EEM spectrum of kihada yellow is shown in Figure 2a. It clearly indicates two peaks derived from berberine, indicating an emission wavelength (λem) at 512 nm excited by the wavelengths (λex) at 353 and 441 nm. The λex/ λem of two peaks observed in the EEM spectra for the shoes and light green twill of the cloth lining in parts b and c of Figure 2 was almost identified with the kihada yellow reference. The values of relative fluorescent intensities of the peaks for each sample were also almost equal (Table 1). These results show that EEM fluorescence is an available tool to distinguish kihada yellow from other yellow dyes in the dye analysis of the Shosoin textiles. The weaker fluorescent intensity for these samples compared to 5696
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the kihada yellow reference is due to the smaller amounts of berberine. Although second-order scattering is observed in Figure 2b,c, the scattering does not directly relate to berberine involved in the samples. For UV-vis reflectance spectrometry, the secondderivative spectrum of the kihada yellow reference is illustrated in Figure 3 (line a); three peaks are clearly observed at 280, 360, and 460 nm. On the other hand, the second-derivative UV-vis spectrum of the light green twill of the cloth lining did not provide the detection of two peaks at 280 and 360 nm (line b in Figure 3). No detection of the characteristic peaks would be possible due to the mixture with other yellow dyes. The results suggest that UV-vis spectrometry is not suitable for the distinction of kihada yellow when coexisting with other yellow dyes. Kariyasu Yellow. Kariyasu yellow, extracted from the stems and leaves of eulalia, involves luteolin, luteolin-7-glucoside, and arthraxin as the main dye molecules (Table 2).24 The hot-water extract from the kariyasu plant has a slightly yellow color, but it complexes with aluminum ions in mordants to the color considered as “kariyasu yellow”. In this study, we used the kariyasu yellow reference mordanted with the lye of camellia ash because it is estimated that people did so in the 8th century from ancient documents. The EEM spectrum for the kariyasu yellow reference mordanted with the lye of camellia ash has two peaks at λex ) 371 nm/λem ) 529 nm at the primary peak and λex ) 459 nm/ λem ) 534 nm at the secondary peak overlapped with the scattering derived from absorption phenomena; this is different from the dye mordanted with potassium alum, which has only one peak at λex ) 441 nm/λem ) 532 nm. The difference results from the pH of these mordants, i.e., aqueous alum is acidic and lye is basic. The yellow dye molecules which compose kariyasu yellow are flavonoids, which have phenolic hydroxy groups in their chemical structures. The resulting complexation of the flavonoids with alum or ash, which gives the yellow color, has a phenolic hydroxide form or sodium/potassium phenolate forms in the flavonoid B ring, respectively (Scheme 1). The EEM for the roll of yellow plain silk, illustrated in Figure 4b, shows a broad peak at λex ) 371 nm/λem ) 519 nm, in which the λex/λem of the peak is almost identical to the kariyasu yellow reference mordanted with the lye of camellia ash and exposed to sunlight for 90 h (Figure 4a,b). The light deterioration of the kariyasu dye molecules gives a lower λem shift from 529 to 519 nm for the primary peak. However, the secondary peak for the sample is too weak to distinguish kariyasu yellow. On the other hand, the EEM of the roll of light green plain silk has two peaks at λex ) 371 nm/λem ) 516 nm and λex ) 441 nm/λem ) 527 nm (parts c and d of Figure 4). The almost identical λex/λem of these peaks between the samples and the reference with ai blue shows the presence of kariyasu yellow. The shift of the secondary peak for λex from 459 to 441 nm, shown in parts c and d of Figure 4, is the result from dyeing over the kariyasu yellow with a blue dye; this was confirmed by using the dye reference silk colored by kariyasu yellow followed by ai blue (Figure 4c). The shift makes the characteristic peak clear because of the avoidance of overlapping with scattering. The values of the characteristic peaks for the light green roll was almost equal (Table 1). These results propose that EEM fluorescence spectrometry distinguishes kariyasu yellow by the detection of the clear peak excited at 441 nm. Compared to the kariyasu yellow
Figure 7. EEM spectra with a λex of 300-600 nm and λem of 500-700 nm for the following: (a) the silk dyed with akane red (reference), (b) the red twill of the cloth lining for the mirror case, and (c) the red plain silk of the sleeveless coat for a dancer.
Figure 8. Second-derivative UV-vis spectra of the following: (a) the silk dyed with akane red (reference), (b) the red twill of the cloth lining for the mirror case, and (c) the red plain silk of the sleeveless coat for a dancer.
Figure 9. Second-derivative UV-vis spectra of the following: (a) the silk dyed with shikon purple (reference), (b) the silk dyed with shikon purple (reference) exposed to sunlight for 200 h, and (c) the purple plain silk of the sleeveless coat for a dancer.
reference, the broader emission peaks and the lower scattering derived from absorption for the samples are attributed to the age degradation of the kariyasu dye molecules. Second-order scattering observed in 2D contour plots does not directly relate with
the kariyasu dye molecules. The UV-vis spectrometry coupled with second derivatization was used to distinguish kariyasu yellow with or without ai blue. The λmax at 470 nm observed in the kariyasu yellow reference exposed to sunlight for 90 h was also identified with the yellow roll of silk (lines a and b in Figure 5). The lower λmax shift from 480 to 470 nm for the reference is due to the degradation of the kariyasu dye molecules. The λmax for the light green roll is also identical to the reference followed by ai blue (lines c and d in Figure 5). These results show that second-derivative UV-vis spectrometry can distinguish kariyasu yellow. Ai Blue. The main dye compound of ai blue is indigo (Table 2).25 The second-derivative UV-vis spectrum for the ai blue reference and the light green plain silk are illustrated in Figure 6. In UV-vis spectrometry following second derivatization of the ai blue reference, a peak derived from indigo was detected at 690 nm. The λmax in the second-derivative UV-vis spectrum of the roll of light green plain silk was almost identical to the ai blue reference, indicating that UV-vis spectrometry is useful for finding ai blue. On the other hand, the EEM fluorescence spectrum for the light green roll had no characteristic peak derived from indigo (Figure 4d). This result shows that EEM fluorescence spectrometry is not useful for finding ai blue used in the Shosoin textiles. Akane Red. Akane red is extracted from madder roots; the dye molecules are different from its source because of the different plant species.26,27 Rubia akane from East Asia has purpurin and pseudopurpurin as its main dye components while Rubia tinctrum is from the West and has alizarin and purpurin as its main dye (23) Gibbs, P. J.; Seddon, K. R. Berberine and Huangbo: Ancient Colorants and Dyes; British Library: London, 1998. (24) Kaneta, M.; Sugiyama, N. Bull. Chem. Soc. Jpn. 1972, 45, 528–531. (25) Balfour-Paul, J. Indigo; British Museum Press: London, 1998; pp 115145. (26) Cardon, D. In Natural Dyes: Sources, Tradition, Technology and Science; Archetype Publications: London, 2007; Chapter 4. (27) Schweppe, H. In Historic Textile and Materials II; Zeronian, S. H., Needles, H. J., Eds.; ACS Symposium Series 410; American Chemical Society: Washington, DC, 1989; Chapter 13.
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components (Table 2). The previous paper described the use of akane from East Asia, which includes Japan, in Shosoin textiles.22 On the basis of this knowledge, Japanese akane was used for preparing the akane red reference in this study. Figure 7a shows the EEM spectrum of the akane red reference. A characteristic peak was observed at λex ) 371 nm/λem ) 607 nm. The peak top at around λex 565 nm was obscure due to overlap with scattering derived from absorption, which is not applicable for the distinction of akane red. The EEM spectrum of the red twill for the cloth lining of the mirror case shows the same peak at λex ) 371 nm, which is a characteristic peak of the akane dye molecules (Figure 7b). In the EEM spectrum for the red plain silk of the sleeveless coat, the characteristic peaks of the akane dye molecules were detected at λex ) 371 nm (Figure 7c). These results indicate that EEM fluorescence is useful for distinguishing akane red from other red dyes in the Shosoin textiles. The weaker emission peak for the samples compared to the reference is attributed to the smaller amounts of the akane dye molecules. Second-order scattering observed in Figure 7 does not directly relate with the akane dye molecules. In the UV-vis spectrometry of the akane red reference, the second-derivative spectrum allowed the detection of three peaks at 470, 500, and 550 nm (line a in Figure 8). The spectrum of the cloth lining for the mirror case and sleeveless coat shows the almost identical λmax at 475 and 505 nm with the reference; the peak at 550 nm was observed as a shoulder peak (lines b and c in Figure 8). These results indicate that UV-vis spectrometry allows for the distinction of akane red in the Shosoin textiles by second derivatization. A larger peak at 575 nm observed in the spectrum of the samples is probably derived from the other coexisting red dye molecules. In the list of treasures dedicated to the Todaiji temple in 752 A.D. by the Empress Komyo (Kokkachinpocho), the color of red twill for the mirror case was described as hi (scarlet). Dye analysis of the red twill clarified that the color hi is from akane red, which agrees with the knowledge gained from the investigation of a photograph of Shosoin red twill in the previous paper.28 Shikon Purple. The dye molecules for shikon purple exist in the bark of murasaki roots and is mainly composed of shikonin (Table 2).29 In UV-vis spectrometry, the second-derivative
spectrum of the shikon purple reference is illustrated in Figure 9 (line a). In the spectrum, the peaks of shikonin were detected at 555, 605, and 645 nm. The second-derivative UV-vis spectrum in the plain purple silk of the sleeveless coat shows that the λmax at 555 and 605 nm was almost identified to the reference (line c in Figure 9). The diminishment of the peak at 645 nm is attributed to the age degradation of shikonin, which was indicated in the shikon purple reference exposed to sunlight for 200 h (line b in Figure 9). The almost identical λmax for the sample with the 200 h-aged reference indicates that UV-vis spectrometry is applicable for finding shikon purple used in the Shosoin textiles. On the hand, EEM fluorescence spectrometry for the purple silk of the coat had no characteristic peak derived from shikonin; this shows that using EEM is not applicable for finding shikon purple in the Shosoin textiles.
(28) Komiyama, J.; Suematsu, M.; Ogawa, S. Dyes History Archaeol. 2005, 20, 102–109. (29) Papageorgiou, V. P.; Assimopoulou, A. N.; Couladouros, E. A.; Hepworth, D.; Nicolaou, K. C. Angew. Chem., Int. Ed. 1999, 38, 270–300.
Received for review February 26, 2009. Accepted May 15, 2009.
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Analytical Chemistry, Vol. 81, No. 14, July 15, 2009
CONCLUSION In this article, we reported on the dye analysis of Shosoin textiles by EEM fluorescence and UV-vis reflectance spectrometry; five dyes, kihada yellow, kariyasu yellow, ai blue, akane red, and shikon purple, were found. EEM fluorescence spectrometry is useful for the distinctions of kihada yellow and akane red. For the distinction of kariyasu yellow, EEM spectrometry needs the detection of a clear emission peak not to be overlapped with scattering. However, it gave no information about ai blue and shikon purple for finding the dyes used in the Shosoin textiles. UV-vis spectrometry allowed for the distinction of kariyasu yellow, ai blue, akane red, and shikon purple through second derivatization. However, limitations in distinguishing kihada yellow through UV-vis spectrometry were encountered when the dye coexists with other yellow dyes in a sample. Parallel usage of EEM fluorescence and UV-vis spectroscopic techniques allows one to find a variety of dyes. The information obtained in these techniques would contribute to the continual conservation of the Shosoin textiles far into the future. SUPPORTING INFORMATION AVAILABLE Additional information as noted in the text. This material is available free of charge via the Internet at http://pubs.acs.org.
AC900428A
