Nuclear Instruments and Methods in Physics Research B 211 (2003) 259–264

www.elsevier.com/locate/nimb

A new 3D micro X-ray fluorescence analysis set-up– First archaeometric applications

Birgit Kanngießer a,*, Wolfgang Malzer a, Ina Reiche b,1

a Institute for Atomic Physics and Teacher Training, Technical University of Berlin, Hardenbergstrasse 36, D-10623 Berlin, Germanyb Rathgen-Research Laboratory of the State Museums of Berlin, Schloßstr. 1a, D-14059 Berlin, Germany

Received 6 February 2003

Abstract

A new 3D micro X-ray fluorescence (micro-XRF) analysis method based on a confocal X-ray set-up is presented.

The capabilities of this new method are evaluated and illustrated with depth sensitive investigations of paint layers in

ancient Indian Mughal miniatures. Successive paint layers could be distinguished non-destructively with a depth res-

olution of about 10 lm. Major and minor elements are detectable and can be discriminated in different layers. New light

could be shed on ancient painting techniques and materials with this new 3D micro-XRF set-up.

� 2003 Elsevier B.V. All rights reserved.

PACS: 07.85.Qe; 82.80.Ej

Keywords: 3D micro-XRF; Depth profiling of elemental composition; Paint layers

1. Introduction

Micro X-ray fluorescence analysis (micro-XRF)

is one of the newest branches of XRF. It has been

developed very rapidly in the past 10 years which is

mainly due to the use of synchrotron radiation.

Nowadays micro-XRF is a well established, non-

destructive analytical method in a large variety of

fields of application like materials science/quality

control, environmental science, geology, life sci-

* Corresponding author. Tel.: +49-30-314-21428; fax: +49-

30-314-23018.

E-mail address: bk@atom.physik.tu-berlin.de (B. Kann-

gießer).1 Present address: Centre of Research and Restauration of

the French Museums, UMR 171 CNRS, Paris, France.

0168-583X/$ - see front matter � 2003 Elsevier B.V. All rights reser

doi:10.1016/S0168-583X(03)01321-1

ence and archaeometry. An overview of the in-

strumentation and the fields of application can befound in [1]. Very soon after the first micro-XRF

set-ups have been built up, they were also used for

the analysis of valuable unique art or archaeo-

logical objects [2–5]. However, the microscopic

excitation spot has been used to perform very local

analysis by 2D elemental mapping or line-scanning

on the sample surface but not to perform investi-

gations in depth. We improved the capabilities ofthe micro-XRF method towards a three dimen-

sional (3D) micro-XRF by realizing a confocal

X-ray set-up and applied it to the investigation of

art-historical objects.

These art-historical objects were ancient

Indian Mughal miniatures. Mughal miniatures,

representations of sovereigns or other important

ved.

260 B. Kanngießer et al. / Nucl. Instr. and Meth. in Phys. Res. B 211 (2003) 259–264

personalities (16–19th century), were produced in

particular workshops in India. These paintings

consist of several well separated polished pigment

layers on paper. Until now, only scarce informa-tion is available on this painting technique and the

artists pigment palette. Moreover, it is known

from the 18th century onwards that there was an

important production of miniatures copying mas-

terpieces from the ‘‘classical’’ period, sometimes by

overpainting old miniatures of low value. With the

possibility to get insights non-destructively into

the chemical composition of the layered pigmentstructure, new clues for the distinction of later

copies from originals may be obtained.

2. Experimental set-up

The confocal X-ray set-up (Fig. 1) consists of

X-ray optics in the excitation as well as in thedetection channel. A micro-volume is defined by

the overlap of the foci of both X-ray optics with

which the chemical composition of samples can be

non-destructively investigated not only laterally

but also into the depth. The depth of the micro-

volume depends on the energy of the exciting ra-

diation, the energy of the fluorescence radiation,

the incidence angle, the angle of reflection, and thesample composition. By moving the sample, the

micro-volume to be analyzed can be displaced

Fig. 1. Scheme of the confocal set-up for the 3D micro X-ray

fluorescence analysis.

laterally or in a direction perpendicular to its

surface. Thus, depth information on chemical

composition can also be obtained non-destruc-

tively. Additionally, a better peak-to-background-ratio can be reached due to the restriction of the

detector field of view. Such a set-up has also been

proposed by Kumakhov [6].

This confocal X-ray set-up was first realized at

the 7T wavelengthshifter beamline, the BAMline,

at BESSY II (Fig. 2). After passing through the

ionization chamber, the monochromatic (17.4 keV)

X-rays were focused by a polycapillary halflens.Working with synchrotron radiation a halflens is

the most suited X-ray optics for the use in the

excitation channel. The halflens has a greater en-

trance diameter as a full lens, thus accepting more

from the quasi-parallel synchrotron beam. Fur-

thermore, beam position fluctuations can be

compensated for to a certain extent. If the syn-

chrotron radiation is already focused down to afew tenth of micrometers by an optical element of

the beamline, an X-ray optic in the excitation

channel is no longer necessary provided the beam

position is stable.

We used a polycapillary halflens with a focus

FWHM of about 30 lm at a working distance of

16 mm. The micro-volume was produced by the

overlap of the halflens focus with the focus of apolycapillary conical collimator (poly CCC) ad-

justed in front of a Si(Li) detector. The focus of the

poly CCC has a FWHM of 20 lm at a working

distance of 1.2 mm.

The use of a poly CCC is much more effective

than the use of a polycapillary full lens in the de-

tection channel, as proposed by Kumakhov [6].

For radiation with an energy below around 8 keV,the poly CCC has a smaller focus size as any

polycapillary lens which can actually be produced.

For radiation with a higher energy the size of the

foci is comparable. Even more important is that

the poly CCC has a greater acceptance angle

leading to a higher transmittance of the radiation.

A disadvantage of the poly CCC is the very small

working distance which aggravates the adjustmentof the sample.

The second detector of the set-up, a drift

chamber detector, was used to monitor the radia-

tion coming from the sample in order to obtain a

Fig. 2. Photo of the confocal set-up at the BAMline, BESSY II.

B. Kanngießer et al. / Nucl. Instr. and Meth. in Phys. Res. B 211 (2003) 259–264 261

global X-ray spectrum. To characterize the micro-

volume formed a 2 lm thick Cu foil was moved

through the beam. The intensity of the Cu Karadiation is plotted in dependence of 5 lm wide

steps. In Fig. 2 the intensity curve is shown for thehorizontal plane with respect to the storage ring.

In this direction the micro-volume had a FWHM

of 55 lm and in the vertical direction a FWHM of

35 lm. In addition to the FWHM, the steepness of

the slope is decisive for the evaluation of the spa-

tial resolution of the method.

3. Experiments and results

Two Mughal miniatures (no. 3 and no. 10)

conserved in the album inv. MIK I 5004 of the

Museum of Indian Art, State Museums of Berlin

were analysed for their paint layer composition.

Fig. 3 shows a classical Mughal miniature dated

from the 18th century (MIK I 5004 (no. 3)). An-other investigated miniature, shown in Fig. 4

(MIK I 5004 (no. 10)), is for stylistic reasons dated

from the second half of the 17th century.

The depth profiles of the represented red fence

of the miniature no. 3, MIK I 5004 is shown in

Fig. 3. They were obtained by moving the minia-ture perpendicular to its surface in 5 lm wide steps

through the X-ray micro-volume. At each step a

fluorescence spectrum was taken with a life time of

100 s. The element depth profile shows the inten-

sity curves of the net peak areas of the La line of

Hg and of Pb. The distance is given in relative

units. For a better comparison, the intensity curves

are scaled to the same maximum height. The depthprofile reveals a layered structure of a 10 lm thick

cinnabar (HgS) layer which was painted on a lead

white (2PbCO3�Pb(OH)2) ground layer of the same

thickness. This result confirms the use of classical

pigments and a layered painting technique of

Mughal miniatures.

The other miniature, shown in Fig. 4 (MIK I

5004 (no. 10)), was investigated at two differentpoints, at the turquoise background and at the

Fig. 3. Micro-XRF depth profiling of a classical Mughal miniature MIK I 5004 (3) dated from the 18th century.

262 B. Kanngießer et al. / Nucl. Instr. and Meth. in Phys. Res. B 211 (2003) 259–264

white poniard. Again, the miniature was moved

perpendicular to its surface in 5 lm wide steps.

The intensity curves extracted from the fluores-

cence spectra at each step are displayed for both

points investigated. They are scaled to the same

maximum height. The graph bars show the maxi-

mum relative intensities of the elements detected.

The element depth profiles for the turquoise

background clearly show a single paint layer with

Cu, Pb and Zn as the main components. These

results are surprising as, up to now, there is no

evidence of the use of Zn and Sn containing white

Fig. 4. Micro-XRF depth profiling of a Mughal miniature MIK I 5004 (10) ‘‘Abdallah Zakhmi’’ of doubtful origin (stylistically dated

to the 17th century).

B. Kanngießer et al. / Nucl. Instr. and Meth. in Phys. Res. B 211 (2003) 259–264 263

pigments in art before the beginning of the 19th

century, at least in Europe. In addition, the in-

vestigation of the white poniard showed a three

layered structure which is in its succession inverted

to the expected one. The first layer on the papercontains only lead. The second layer is again a

mixture of mainly Pb, Zn and Sn. In addition,

there seems to be a very thin third layer containing

mainly Pb on the top.

Thus, this painting represents either the first

scientifically proved sample of an early use of zinc

white in India or it is simply a copy manufactured

in the 19th century. The analysis and comparisonof ancient zinc white pigments from India will

contribute to finally solve this problem.

4. Conclusions and perspectives

The first archaeometric results show the po-

tential of this new 3D micro-XRF set-up. Succes-sive paint layers were distinguished with a

resolution of about 10 lm. Major and minor ele-

ments are detectable and can be distinguished in

different layers even if the same element is present

in successive layers. This opens up the way for the

non-destructive investigations of paint layers, un-

derdrawings, metal surfaces (gilding, corrosion,

protection), glass surfaces/glazes, inclusions in

gemstones etc. which can contribute to answer

questions in archaeology and art history.

For a better quantification of the element depth

profiles a deconvolution from the sensitivity profile

and the correction for absorption effects will be thenext steps.

However, of course, the new 3D micro-XRF

method is not restricted to archaeometry. It can

make important contributions to all fields of ap-

plication mentioned in the introductory remarks,

as environmental science and quality control in

materials science. Another very interesting re-

search field is, for example, the analyses of histo-logical samples in life science. Furtheron, a

combination of the 3D micro-XRF with Micro-

XANES for chemical speciation and with micro-

XRD for phase information will be a unique tool.

Acknowledgements

We gratefully acknowledge A. Bjeoumikow and

N. Langhoff, IFG, for placing the half lens at our

disposal. Likewise we are grateful to Marianne

Yaldiz, Raffael Gadebusch and Toralf Gabsch,

Museum f€uur Indische Kunst, for placing the

Mughal miniatures at our disposal. Thanks are

also due to Heinrich Riesemeier and Martin

Radtke, BAM, for their support during the

264 B. Kanngießer et al. / Nucl. Instr. and Meth. in Phys. Res. B 211 (2003) 259–264

beamtime. This work was partially supported by

the DFG.

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