Application of XAFS in Archaeology
I. Nakai, M. Matsunaga, M. Adachi, K.-I. Hidaka
To cite this version:
I. Nakai, M. Matsunaga, M. Adachi, K.-I. Hidaka. Application of XAFS in Archaeology. Journal de Physique IV Colloque, 1997, 7 (C2), pp.C3-1033-C3-1034. <10.1051/jp4:19972131>.
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L PPHrS IV FRANCE 7 (1997)
Colloque C2, Suppltment au Journal de Physique I11 d'avril 1997
Application of XAFS in Archaeology
I. Nakai, M. Matsunaga, M. Adachi and K.-I. Hidaka*
Department of Applied Chemistry, Faculty of Science, Science University of Tokyo,Kagurazaka,
Shinjuku, Tokyo 162, Japan
* University of Tsukuba, Tsukuba, Ibaraki 305, Japan
Abstract. X-ray fluorescence XAFS technique was successfully applied to the archaeological study to find
colorant elements in old glass samples and to characterize the chemical states of iron in the ceramic sherds
excavated from an archaeological site in Turkey. The origin of red color of the mosaic glass is found to be due
to the colloidal copper particles in the glass. Blue color is attributed to divalent cobalt. Fe K-XANES spectra
revealed that the color of the sherds changes from black, gray, brown, to orange with increasing the absorption
edge energy. The gray ceramics typical for Phrygia age were produced in a reducing condition. The creatn
color of the central Anatolian Iron Age could not be related with the oxidation state of iron.
1. Introduction
Various colors in glasses are caused by metal ions in them [l]. They are usually elements belonging to the
transition rows of the periodic system, which absorb characteristic frequencies of visible region as a result of the
d-d electronic transitions. Similarly, iron is a key element to understanding the color of various types of pottery.
Since this kind of information is important in understanding the manufacturing technique of glass wares and
potteries, we have investigated ancient colored glasses from middle east and pottery sherds excavated from
archaeological site of Kamall Kalehoyiik, Turkey by using XAFS technique. This is the first report of the
archaeological application of this technique to ancient pottery analysis.
2. Experimental
Samples used are mosaic glasses from Dome of Hagia Sophia build in 537 in Istanbul, Turkey and ceramic sherds
from Kaman Kalelioyiik, Turkey [2]. These sherds were produced by Hittite and Phrygian civilizations. The
colors of the sherds are red, gray, yellow, cream and black. X-ray absorption spectra were measured at Photon
Factory (PF) in the National Institute of High Energy Physics, Tsukuba, Japan with a S i ( l l 1 ) double crystal
monochromator. Two dimensional chemical state analysis of iron in the ceramic sherds was carried out at BL4A using Si(Li) S.S.D. as a detector and small X-ray beam (width 800km and height 400 +m ). EXAFS data were
obtained at BL-6B using a fluorescent X-ray detector [3]. The K-edge spectra of the glass samples were
measured in this mode. Reference spectra of standard compounds and minerals were also measured at BL-4A
and BL-6B. The edge energy is defined by a half maximum value of the white line peak of each XANES spectrum.
3. Results a n d Discuseion
Figure 1 shows Cu K-edge XANES spectra of the colored glasses and reference materials after having been
normalized to the height of the edge jump. Radial structure functions of their EXAFS~oscillationobtained from
the Fourier transforms of k3X(k)are given in Fig 2. A comparison of the spectrum of the red mosaic glass (Fig. l
(b)) with that of the Cu metal (Fig.l(a)) indicates that Cu in the mosaic glass exists as copper metal. This finding
is supported by the corresponding radial structure functions given in Figs. 2(a) and (b). It is well known
hypothesis that colloidal particles of metallic copper is the origin of the red color in the copper red glass [l].
Figures 1 (d) and (f) are XANES spectra of a green mosaic glass and a green Egyptian glass and their FTs are
given in Figs. 2 (d) and (f), respectively. The results indicate that oxidation state of copper in the mosaic glass
is monovalent while it is divalent in the Egyptian glass. The Cu+ is d" ion and is not responsible for the green
color which is the color of divalent copper (cf. (e) and (f)). Therefore, the origin of the green color in the mosaic
glass could be ascribed to another ion. Similarly, it was found that c o 2 +was responsible for the blue color of the
mosaic glass and Egyptian glass.
Figure 3 is a summary of the results for the shreds analysis which shows a correlation of the color of the sherds
and Fe K-edge energy. The difference in the analyzed spot in a sherd, i.e. surface or inside accounts for the
diversity of the data. The color of the ceramic sherds changes from black, gray. brown to orange with increasing
the edge energy. When we compare the edge energy of the reference samples with that of the sherds, it is found
that the black sample gives the lowest energy close to that of the magnetite region, and similarly, gray to silicates
containing both ferrous and ferric ions, reddish brown to hematite and orange to ferric silicate minerals.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jp4:19972131
JOURNAL DE PHYSIQUE IV
C2-1034
(a) Cu metal
...
-( a ) Cu metal
( b ) red mosaic glass
- - (C)
Cu20
. .. ... (d)green
- (b) red mosaic glass
-( c ) c u 2 0
mosaic glass
...
-(e)CuO
. (d)ereett
mosaic gloss
(e)CuO
(t) Egyptian green
.... ( 0 Egyptian green
glass
glass
P\
keV
Figure 1: Cu K-edge XANES spectra of glass samples
Figure 2: Fourier transforms of the k' x (k) of glass samples
Two dimensional chemical state analysis of a section (Fig. 4(a) ) of so called "golden mica slip ware." (dated
Phrygian age) was carried out and XANES spectra measured at points A: B, C and D in Fig. 4(a) were given in Fig.
4(b). The colors of the points A and D are pale orange while it is gray at point C. It can be seen from Fig 4(b)
that the spectra shift to higher energy from C to A indicating that iron at the surface is more oxidized than that in
the inside. From these observation it is possible to deduce that this pottery was fired once in reducing condition
then under oxidizing condition in a kiln. Our analysis showed that the gray ceramics typical for Phrygia age
were produced in reducing conditions. The cream color of the central Anatorian Iron Age creamware could not
be related with the oxidation state of iron. The information derived from the Fe K-XANES spectra of pottery
sherds is the electronic structure of iron in them, which is determined by mineral sources, their relative composition and the thermal history of each clay received during firing conditions, which may differ from kiln to kiln.
In concIusion, present study indicated that XAFS spectroscopy offers many advantages over conventional
chemical speciation techniques such as Mossbauer spectroscopy and XPS. XAFS allows us to carry out two
dimensional chemical state analysis, whose spatial resolution is determined by the beam size; e.g., with a focusing
optics we can currently obtain microbearn of a few pm order at BL-4A. Since the excitation source is hard X-rays,
the method is truly nondestructive analysis that can be done in air. These characteristics are particularly
important in archaeological application in which samples are precious cultural heritage. XAFS requires no
special vacuum chamber like XPS and no restriction in sample sizes and their materials, i.e. they may be metals,
ceramics, cloths, glasses, etc. Moreover, XAFS technique is applicable to most of the elements with atomic number, practically. greater than 13(=A1), whereas Mossbauer spectroscopy is limited to a small number of elements.
References
[ l ] Doremus R.H., Glass Science (John Wiley & Sons, New York, 1973)pp.327-330.
[2] Mori M.,Omura S. Bull. Middle E a s t e r Culture Cerrter Jnpnw, 8 (1995) 1-55.
[3] Lytle F.W., Greegor R.B., andstrom D.R.,Marques E.C., Wong J.. Spiro C.L., Huffman G.P.Hugins F.E..A'ucuc[. Instr.
(1984)542-548.
orange
buff
light bmwn
brown
&dish brown
darkbrown
yellowish cgray
light hlack
light gray
d& hlack r
hlack
silicatd~C.~?)
magnetite
...
Meth. 226
..
---S
-.
-.
.....
..
- ..
-..- . ..
.-
pyrite
.Fe mnal
energy (eV)
Figure 3. Fe K-edge energy of ceramic
sherds and their colors
energy(keV)
Figure 1:Two dimensional XANES analyses of a ceramic sherd.
(a) sample section, (b) Fe K-edge XANES spectra