Applications of Micro XRF for the Analysis of Traditional Japanese "Ainu" Glass Beads and other Artifacts

Transcription

1 Applications of Micro XRF for the Analysis of Traditional Japanese "Ainu" Glass Beads and other Artifacts K.Sugihara 1, M.Satoh 1, Y.Hayakawa 2, A.Saito 3 and T.Sasaki 4 1 Seiko Instruments Inc., Chiba, Japan 2 Tokyo National Research Institute of Cultural Properties, Tokyo, Japan 3 Science University of Tokyo, Tokyo, Japan 4 Tokyo National Museum, Tokyo, Japan ABSTRACT Ainu people, one of Japan s early tribes, made several types of glass in accordance with traditional Ainu customs. Most beads were made in the 1800s when making homogenous glass was a difficult task. The homogeneity of Ainu glass beads was measured by micro and conventional XRF method of analysis. These analyses showed no significant difference in chemical composition throughout the volume of the beads. We therefore concluded that Ainu glass beads are homogeneous. The chemical composition of Ainu glass beads can be classified by using three parameters: the composition of the raw material, mixing ratios, and the process by which the beads are made. This classification method can be used to determine where the beads were made. Traditional Japanese artifacts have a unique design and a beautiful color. The area of an x-ray probe is larger than the area of each pattern, and this makes it difficult to analyze the coloring in patterns of such artifacts. Micro XRF techniques were used to eliminate this problem. ANALYTICAL PRECISION OF MICRO XRF A high-brightness micro X-ray beam device was developed for the analysis of small samples (sub-millimeter). The analytical precision of the micro XRF was compared to the conventional bench-top XRF by analyzing Ainu-Tama, a traditional Japanese glass. The composition of many Ainu-Tama have been measured by micro XRF techniques.

2 This document was presented at the Denver X-ray Conference (DXC) on Applications of X-ray Analysis. Sponsored by the International Centre for Diffraction Data (ICDD). This document is provided by ICDD in cooperation with the authors and presenters of the DXC for the express purpose of educating the scientific community. All copyrights for the document are retained by ICDD. Usage is restricted for the purposes of education and scientific research. DXC Website ICDD Website -

3 INSTRUMENTS MICRO-XRF (SEA5000Series) The SEA5000 series instrument equipped with a high-brightness micro X-ray beam, can irradiate a very small area of a sample. A CCD camera allows one to accurately direct the beam upon a small spot of a specimen. Below is a schematic diagram of the micro XRF and a uhotorrrauh of SEA5230 (Seiko Instruments Inc.). Controller Fig. 1-1 Schematic diagram of micro XRF Fig. 1-2 SEA5230 BENCH-TOP XRF(SEA2000 Series) The SEA2000 series has a beam size of a IOmmQ,. It can analyze a variety of sample types including large bulks, powder, and liquid samples. Below is a schematic diagram of the bench-top XRF and a photograph of the SEA2120 (Seiko lnstnlments Inc.). Amplifr8r/Analyzer r lg. Schematic diagram of bench-top XRF

4 AINU-TAMA A JAPANESE TRADITIONAL GLASS Ainu-Tama glass is a symbol of the Ainu people culture. Large light-blue colored beads are very valuable. Below is a photograph of a typical glass bead. Fig. 3 AINU-TAMA glass

5 MEASUREMENT POINTS We compared results of the micro XRF with results of the bench-top XRF. The SEA5230 was used to measure glass beads at the 5 points shown in figure 4. The SEA2 120 was then used to measure glass beads at their center. COMPARISON OF THE ELEMENTAL CONCENTRATIONS OBTAINED FROM A Fig. 4 MEASURING POINTS MICRO XRF UNIT AND A BENCH-TOP XRF UNIT The average value of 5 measurements of various oxides in the same glass bead by the SEA2120 was plotted on the X-axis. Individual values for same glass bead, measured by the SEA5230, were plotted on the Y-axis (see figure 5). The concentrations of the main components of glass(si0 2 and 3 other oxides)were selected. Si02 PbO #BUD $ 5TDO E IO / moo t,ow 1500 moo IIDD mi)o 6500 SEA2120 SEA2120 ZiM Z3M mw LBrn,103 4 M litm * nm r,m 9u) K20 7M _-,111 *ml L7.M zml 2IM SFA2120 lzc!l r 1 oc 1 I SM z c: 600 J 100 2l-a CaO 000 OUI Ltm,u) Loo 800 I 11M SEA2120 Fig. 5 Comparison of results obtained from the micro XRF and the bench-top XRF

6 Error bars in the Y-axis indicate the standard deviation obtained from the SEA5230. The average values obtained from SEA5230 shows no difference from the values obtained by SEA2120. Our data shows that elemental segregation in some samples is larger than the standard deviation of our measurements of concentration, however we believe the roundness of the sample surface may be the reason for these differences. The diameter of a glass bead is around 10 to 20 mm and therefore is not large enough to consider as a flat surface. We conclude that the source of the difference in the measurements is due to the shape of the beads and not due to inhomogenity in the distribution of elements in the beads. CLASIFICATION OF GLASS BEADS BY PRINCIPAL COMPONENT ANALYSIS 96 kinds of AINU-TAMA glasses were analyzed by SEA5230. Some of them are shown in table 2. Table2 Some of raw data obtained from SEA5230 Sample No Na 2 O MgO Al 2 O 3 SiO 2 K 2 O CaO TiO 2 MnO Fe 2 O 3 CuO ZnO PbO SnO 2 Sb 2 O In order to classify the data, Principal Component Analysis (PCA) is applied. PCA, a dimension reduction technique, takes 96 kinds of analyzed values with 14 independent variables (Na 2 O,SiO 2,.) and constructs a new set of eigenvectors that are linear combinations of the original variables. The eigenvectors can be thought of as a new set of orthogonal plotting axes. The primary axis, termed principal component one (PC 1 ), is the single vector which describes the greatest variability in the data. Subsequent PC s, ranked by decreasing eigenvalue, describe successively less sample variability. It is the purpose of PCA to decompose the data matrix of independent variables into PC s. 2)

7 CLASIFICATION BASED ON PC1 AND PC2 The factor loading map of PC, and PC, is shown in figure 6-l. The factor score maps of PC, and PC, are shown in figure 6-2. Glass beads can be divided into two groups. PbO has the strongest influence on PC, and contributes the most to this classification. NqO and K,O are characteristic of PC,. In figure 6-2, on the left side, Na,O becomeshigher as you move up to the PC, and K,O becomes higher as you move down the PC,. Fig. 6-l -1 Factor loading map of PC, and PC, w Factor score map of PC, and PC, 1 Fig. 7-1 Factor loading map of PC, and PC, Fig. 7-2 Factor score map of PC, and PC., Above are the factor loading map (left) and the factor score map (right) of PC, and PC,. In the factor loading map, Sb,O, and SnO, are distinctive. The group including Hi-PbO (See Fig.6) are divided further into two groups by Sb,O, and SnO,

8 MAPPING ANALYSIS OF JAPANESE ARTIFACTS Mapping analysis was applied to the measurement of a ceramic dish with painted flowers and RADEN, which is a traditional Japanese decoration, using thin shell and metal with Japanese lacquer. Experimental conditions are shown in table 3. Table 3 Experimental conditions employed for X-ray mapping analysis X-RAY MAPPING OF COLORED IMAGES IN A CERAMIC DISH Pictures of the ceramic dish and X-ray mapping images are shown in figure 8. Fe Fig. 8 X-ray mapping images of DISH Mll

9 The picture displays several kinds of color: red for petals, green for leaves, etc.. According to X-ray mapping images, these colors contain several elements. For example, red and green are made of Mn, Co, Pb, Cr and Zn. Semi-quantitative analysis can be done easily by using the FP method. Analyzed values are shown in table 4. Table 4. Semi-Quantitative analysis of Red and Green areas Red(%) Green(%) MnO CoO Pb3 O Cr2 O ZnO X-RAY MAPPING IMAGES OF DISH-2 X-ray mapping images of another part of a ceramic dish are shown in figure 9. Fe Cr Co Ti Fig. 9 X-ray mapping images of DISH-2 An overlay map is shown in figure 10. Fe was found around the edges of the flower. Blue and yellow colors in petals contained Co and Ti, respectively. The overlay map is similar to the actual picture. Fig. 10 Overlay map

10 169 X-RAY MAPPING IMAGES OF RADEN X-ray mapping images of Raden are shown in figure 11. Cu Zn Ca K Fe Fig. 11 X-ray mapping images of Raden Raden is a traditional Japanese decoration, a thin shell and metal are built in the base and covered with Japanese lacquer. Ca and K were found in the area of the petal, therefore the petal is most likely made of shell. 7 pieces of brass (Cu- Zn alloy) were found in X-ray mapping images, although only 5 pieces can be seen in the actual picture. Two pieces of brass may be covered by Japanese lacquer

11 CONCLUSION An X-ray unit with a very bright, micro focus X-ray beam has recently been developed for the analysis of small samples (sub-millimeter). The standard deviations of measurements with a micro XRF were compared with those from a conventional bench-top XRF for the analysis of Ainu-Tama glass. The chemical compositions of many Ainu-Tama have been evaluated by the micro-edxrf. The results of the mapping analysis of Japanese artifacts are also presented. 1) Analytical precision of micro XRF No significant difference was found in measurements made by the micro XRF unit equipped with a 2mmQ> X-ray beam and a conventional bench-top XRF equipped lomm<p X-ray beam. The elemental segregation of some glasses was larger than the deviation of analyzed values obtained from Ainu-Tama glasses by using a micro XRF unit. 2) Analysis of Ainu-Tama, traditional Japanese glass beads. Ainu-Tama glass was determined to be almost homogeneous. The chemical composition of glass beads colored with light blue can be classified into two categories by use of the content of lead by PCA (Principal Component Analysis). Glass, including glass with a high content of lead, can be further divided into two groups containing antimony and tin. 3) Mapping analysis of Japanese Artifacts A flower design drawn on a ceramic dish (30cmQ) was measured for mapping using the SEA5230 micro XRF with a large sample chamber. Coloring elements were identified by elemental mapping images, and components of several pigments were determined by the FP method. We conclude that the micro XRF analyzer is a useful and non-destructive tool for measuring the elemental composition of intricate designed traditional Japanese. REFERENCE 1) H. Sakata, Adv. X-ray Chemical Ana. Japan, 22, p. 135( 1991) 2) M.P. Nelson, J.F. Aust, J.A. Dobrowolski, P.G. Verly and M.L. Myrick, Anal. Chem, 70, p.73(1998)