INTODUCTION
Wall-paintings fragments from the Roman Corinth (Greece), were dated to the early Imperial period through late antiquity. The wall-paintings were decorating
private and public buildings, one area east of the Theater and two domestic buildings, located southeast of the Roman Forum. The original motifs included figural
representations, floral and geometric ornaments and architectural motifs1. Previous analyses2 of wall-painting micro-samples by means of OM, SEM-EDX and XRD
techniques revealed a limited pigment palette, composed of Egyptian blue, naturally occurring iron-based ochres (limonite, goethite, hematite), cinnabar,
celadonite and lead white. SEM-EDX analyses on cross-sections identified the presence of minor elements (like As, Pb) dispersed in yellow or red pigments and Cr rich
mineral grains within the ochre or in Green Earth rich painted layers. In-situ XRF results were rather confusing regarding the role of Pb and As. 3D Micro XRF analysis was
applied in a non-invasive manner aiming at:1) reconstructing the arrangement of the various painted layers and 2) revealing and confirming, with spatial resolution of
few tens of μm, 3D spatial correlations between major and minor/trace elements in the individual pigments.
EXPERIMENTAL
The set up used comprised of the following main components:
high power (3 kW), line focus, Mo-anode, diffraction X-ray
tube (operated at 45kV/40mA); 3 silicon drift X-ray detectors
(SDD), each serving different purpose, namely: (1) detection
of X-ray fluorescence (XRF) radiation in a “standard”
geometry, (2) detection of XRF radiation in a confocal
geometry, (3) detection of the transmitted beam; X-ray
polycapillary lens focusing the primary beam emerging from
the X-ray tube; polycapillary conical collimator positioned in
the confocal channel; computer controlled, motorized stages
for sample 3D translation and rotation and for the confocal
lens alignment in 3-spatial dimensions; a laser triangulation
position sensor; optical microscope coupled to a CMOS
camera providing real-time image of the analyzed region of
the sample.
polyCCC confocal detector
RESULTS
3D-Micro XRF analyses were performed in five painted plaster fragments. Single or composite
painted layers with various combinations of blue, green, red and white pigments were examined.
CORRELATION OF As & Pb WITH Fe IN RED OCHRE PAINT LAYER
The 3D reconstruction of the morphology of a painted plaster Cor 43b (optical microscope crosssection image in Fig.3) was shown in Fig.4. A clear association of both Pb and As with the Fe-ochre
rich layer was observed.
Figure 4: (a) Optical image of Cor
43b with scanned region dimensions:
120 μm x 1440 μm x 293 μm, xyz
scanning spacing: 40 μm x 40 μm x 3
μm; (b) Volumetric reconstruction of
3D spatial distribution of Cu-Kα
(Egyptian Blue), Fe-Kα (Red Ochre),
Ca-Kα (Egyptian Blue, Ground, Pb-Lβ
and As-Kβ characteristic peak
intensities; (c) Translation in z-axis of
the elemental distribution patterns.
Cor43b
Figure 3: Image from optical microscope
of Cor43b (blue on red on white ground).
sample in
measuring
position
Region 1
Maximum peak counts in region 1
Ca-Ka= 408
Cu-Ka= 80
Fe -Ka=1946
As -Ka= 3029
Pb -Ka=1213
Zn- Ka= 365
SDD-2
polycapillary (primary beam)
Maximum peak counts in region 2
Ca-Ka=277
Cu-Ka=2787
Fe -Ka=645
As -Ka= 223
Pb -Ka=223
Zn- Ka= 70
SDD-3
X-ray
tube
Figure 1: NSAL X-Ray Microanalysis set-up - Measuring geometry.
The scanning and the data acquisition were controlled by the
IAEA developed SPECTOR/LOCATOR software3. Spector
supported also the extraction of the net characteristic X-ray
peak areas, whereas AVIZO 6.04 visualization software was
used for volumetric reconstruction of the collected data. The
depth resolution was 23 μm at Cu-Kα with a filtered exciting
beam (50 µm Ni + 12.5 µm Mo composite filter).
Figure 5: Fine-tuned 3D Micro-XRF scans of selected regions of sample Cor43b. The volumetric reconstruction refers to a
red (1) and blue (2) rich micro-volume, respectively. Scanned region dimensions: 56 μm/55 μm/55μm, scanning spacing
5.6 μm/5.5 μm/5μm. The results of the more detailed reconstruction further confirm not only the association of Pb and As
with the red paint layer but also the co-existence of Pb and As (most likely included in the same compound or mineral).
CORRELATION OF Cr WITH Fe IN GOETHITE (YELLOW OCHRE) PAINT LAYER
A grain of chromite as well as its corresponding EDX spectrum were shown in Fig.6. A clear
evidence of the presence of Cr in the Fe-ochre rich layer was found. In Fig. 6a an optical
microscope cross-section image of sample Cor13 composed of a goethite (FeO(OH)) top layer on
white ground was shown. SEM analysis in the backscattering mode (Fig. 6b) revealed the presence
of large grains, EDX analysis further confirmed the presence of chromite ((Mg,Fe2+)(Cr,Al)2O4).
(b)
(a)
7
In-situ XRF analyses and laboratory micro XRF measurements
were rather confusing regarding the position of certain
elements appearing in elevated amounts. For example in Fig.
2, it was not clear if the strong presence of Pb and As was
correlated with the red or blue paint layer or an association
6
43b
Cu
Ca
Counts/Chanel
Fe
4
Sr
Mo
10
3
10
4
6
3
(a)
Pb, As
Pb
As
2
chromite
5
existed with another paint layer
(lead white preparation layer).
10
5
6
4
MOTIVATION
10
Region 2
8
10
12
14
16
18
20
Energy (keV)
Figure 2: Micro-XRF (sum)
spectrum from analysis on
extended scanned area of
sample Cor 43b(blue on red on
white ground) indicating strong.
3D Micro XRF analysis was
applied
in
a
non-invasive
manner aiming at: 1) reconstructing the arrangement of the
various painted layers and 2)
revealing and confirming, with
spatial resolution of few tens of
micrometer, 3D spatial correlations
between
major and
minor/trace elements in the
individual pigments.
Figure 7: Optical microscope image of
the surface of Cor13 sample depicting
the scanned region (Scanned region
dimensions:
0μm/1500μm/243μm,
scanning spacing 0μm/25μm/3μm.
Figure 6:(a) Optical image of
(c)
the sample Cor13 (b) SEM
backscattering
image
of
Cor13, (c) EDX spectrum of
chromite (Mg,Fe2+)(Cr,Al)2O4)
grain. Apart from chromite[3];
egyptian blue [4]; goethite,
biotite, calcite with Pb [5];
dolomite, gypsum [6]; calcitic matrix with dispersed Pb [7],
are also shown in the SEM image.
Figure 8: The graphs of Fe and
Cr characteristic radiations
present
their
in-depth
distribution in the scanned
region. The presence of Cr is
strongly correlated with Fe. All
acquired
spectra
were
analyzed by means of AXIL
software in order to account
properly for the spectral
interference of Fe-Kβ escape
peak (5.32 keV) with Cr-Kα
(5.41 keV).
By using 3D Micro-XRF scans a strong evidence for the co-existence of Cr in the Fe-ochre rich layer
has been found. The presence of chromite clearly marked the formation of the Feoxides/hydroxides from the ultra basic parent rocks.
CONCLUSIONS
 The laboratory 3D Micro XRF non-invasive analysis of Roman period painted plaster fragments offered 3D reconstruction and imaging of the various pigments
and painted layers.
 The 3D analysis confirmed the existence of important elemental correlations with micrometre resolution.
Selected References
1. Lepinski, Roman Wall Paintings from Panayia Field, Ancient Corinth, Greece: A Contextual Study. Ph.D. Dissertation, Bryn Mawr College, 2008.
2. Ch. Apostolaki, V. Perdikatsis, E. Repuskou, H. Brecoulaki, and S. Lepinski, “Analysis of Roman wall paintings from ancient Corinth/Greece.” Proceedings of the international Conference Amireg 2006 Chania pp.729-734.
3. M. Bogovac, M. Jakšić, D. Wegrzynek, A. Markowicz, Nucl. Instr. Meth. in Phys. Res. Section A, 2009, 608, 157.