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R E S E A R C H A R T I C L E Open Access
Identification of artificial orpiment in the interior
decorations of the Japanese tower in Laeken,
Brussels, Belgium
Marc Vermeulen
1*
, Jana Sanyova
1
and Koen Janssens
2
Abstract
In this paper, we used a multi-technique approach in order to identify the arsenic sulfide pigment used in the
decorative panels of the Japanese tower in Laeken, Belgium. Our attention was drawn to this particular pigment
because of its relatively good conservation state, despite its known tendency to fade over time when exposed to
light. The pigment was used with different painting techniques, bound with oil and urushi in the lacquers and
with an aqueous binder in the mat relief panels. In the latter case it is always applied as an underlayer mixed with
ultramarine blue. This quite unusual pigment mixture also shows a good state of preservation.
In this study, the orpiment used for the Japanese tower has been identified as an amorphous arsenic sulfide glass
(As
x
S
x
) with the aid of light microscopy, PLM, SEM-EDX and Raman microscopy. The pigment features different
degrees of As
4
S
4
monomer units in its structure, also known as realgar-like nano-phases. This most likely indicates
different synthesis processes as the formation of these As
4
S
4
monomers is dependent of the quenching
temperature (Tq) to which the artificial pigment is exposed during the preparation phase.
Keywords: Orpiment, Arsenic sulfide glass, Raman spectroscopy, Polarized light microscopy
Introduction and historical context
In characterization studies of arsenic sulfide pigments,
there is a high probability that conclusions regarding the
exact nature of the compounds present are drawn pre-
maturely. In many cases, the encountered arsenic sulfide
is recognized as being a mineral orpiment while in reality
it appears to be pararealgar - the yellow degradation phase
of realgar - while in others, distinction between natural
and artificial orpiment is not made. Contradictions about
the exact nature of arsenic sulfide pigments can also be
found in published scientific literature or pigment ency-
clopedias, sometimes confusing realgar with an arsenic
sulfide glass of unknown composition [1]. So-called artifi-
cial orpiment can be produced using two different pro-
cesses, wet and dry, using different starting materials [2,3].
In any case, arsenic sulfide pigments are the result but
the structure and properties of the reaction products can be
different. To understand its composition and characteristics,
a multi-technique approach is required. Each used tech-
nique, from SEM-EDX to Raman spectroscopy and polar-
ized light microscopy, can increase the knowledge about
the processes behind artificial arsenic sulfide. Although
the use of such a pigment in a 20th-century artifact seems
rather uncommon, its good conservation state is even
more striking when one considers how instable this ma-
terial is over time.
By the end of the 19th century, Europe was fascinated
by Asia, notably by China and Japan. The latter country
was only opened to Western commerce and travellers in
1853 [4-6]. This fascination had influenced the arts as il-
lustrated by the many Japanese influences in impressionist
paintings [6,7], in literature [4] or in architecture with the
example of La Pagode, a Parisian movie theater/dance hall
built in 1896 [8]. All of these Japanese-inspired creations
date from the period 1850–1910. This movement, also
called Japonism, was most likely stimulated by the world
expositions organized in Europe by the end of the 19th
century. While the 1867 and 1878 fairs witnessed the first
exhibition of Japanese artifacts and rapidly promoted this
form of art in Europe [4,5], the Japan-like representation
* Correspondence: marc.vermeulen@kikirpa.be
1
Laboratory of polychrome artifacts, Royal Institute for Cultural Heritage, Parc
du Cinquantenaire 1, B-1000 Brussels, Belgium
Full list of author information is available at the end of the article
© 2015 Vermeulen et al.; licensee Springer. This is an Open Access article distributed under the terms of the Creative
Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and
reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain
Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article,
unless otherwise stated.
Vermeulen et al. Heritage Science (2015) 3:9
DOI 10.1186/s40494-015-0040-7
reached its climax during the world fair in 1900 in
Paris with the Panorama du tour du Monde and its three
imposing towers [9]: one Moorish in style, another one
Hindu and the third one, the most massive, Japanese
(Figure 1). King Leopold II of Belgium visited this Panorama
du tour du monde in 1900 and hired the architect Alexandre
Marcel to build a pagoda similar to the Japanese one
for the fair on the Royal domain in Laeken, Brussels,
Belgium [10].
The construction of this Japanese tower took three
years and it was inaugurated in 1905. The main entrance
porch was taken from the original Parisian pagoda while
other elements such as the sliding doors and decorated
panels were shipped from Japan; in some cases, these ar-
tifacts were re-used elements from disassembled tem-
ples. Finally, some elements were created in Europe, by
European craftsmen [10,11].
Its fate has not been as bright as the King had intended:
due to construction defects, the first floor allegedly served
as his unofficial office for only one year and was then
abandoned, together with the four other floors [11]. After-
wards, the lobby, the main staircase and the ground floor
were transformed into the Far East Museum managed by
the Royal Museums of Art and History, Brussels, Belgium.
Due to their limited access, the first to fifth floors did not
suffer as much from the visiting public as the ground
floor, but the materials present here did degrade drastic-
ally due to unsuitable conservation conditions resulting
from the aforementioned construction defects. An inter-
disciplinary study of the tower for a later conservation/
restoration has been undertaken to identify the materials
used in the decorative elements
a
. During this investiga-
tion, many sulfur-containing pigments such as mercury
sulfide, ultramarine blue or arsenic sulfide have been iden-
tified. These pigments present different levels of degrad-
ation based on their type and localization within the
tower. For example, the mercury sulfide pigment was gen-
erally found to be much degraded on the fourth floor of
the tower (Figure 2a) whereas arsenic sulfide found one
level below, with more or less the same light exposure, did
not exhibit any apparent degradation (Figure 2b). This
apparent stability of arsenic sulfide, a pigment notori-
ous for its instability, seemed rather uncommon. The
light-induced degradation process of arsenic sulfide trans-
forms it from bright yellow arsenic sulfide (As
2
S
3
)to
white/transparent arsenic trioxide (As
2
O
3
) [12-14]. This
phenomenon of fading seems to be a surface alteration,
the lower part of the paint system being unaffected [15].
Similarly, red vermillion (HgS) is converted to grey/black
calomel (Hg
2
Cl
2
) by exposure of light as can be observed
on the red decorative panels of the fourth floor of the
tower [16]. Previous studies [2,3] have focused on the syn-
thesis and analysis of arsenic sulfide pigments and five
major types of arsenic sulfides have been identified based
on their origin or manufacturing processes: natural orpi-
ment obtained from mining, so-called artificial orpiment
obtained from a wet process (never encountered in any
works of art up to now) and from several dry processes
(three types depending on the original reactants) [17]. Ex-
cept for the dry process pigment obtained from natural
orpiment and sulfur as starting materials which can be
considered as artificial orpiment, all of the other forms
have to be referred as arsenic sulfide glass [18].
To understand this unusual arsenic sulfide stability, the
characterization of the pigment used in the panels has
been undertaken using a multi-technique approach. Since
arsenic sulfide is a good Raman scattering material,
Raman spectroscopy (MRS) along with polarized light
microscopy (PLM) seemed the best suited methods to
identify the type of arsenic sulfide present in the tower.
Nonetheless, scanning electron microscopy coupled with
X-Ray detection (SEM-EDX) also seemed useful to some
extent. On the other hand, more sophisticated methods
such as microscopic X-Ray diffraction (μ-XRD) or time of
flight secondary ion mass spectrometry (ToF-SIMS) did
not seem very promising due to the poor ionization of the
arsenic in the case of SIMS and the lack of signal - except
for the broad band characteristic for amorphous material -
in the case of μ-XRD.
Materials and methods
–Samples
Among 165 samples taken from the tower for a
complete technical study, a total of 24 samples
containing arsenic sulfide pigment and sampled on
different floors were selected. The samples were
Figure 1 Photograph of the Panorama du tour du monde with,
on the South-East side (left hand side of the photograph) the
Hindu style tower and on the North-East side the Japanese
pagoda that was used as model for the Japanese tower in
Laeken, Belgium.
Vermeulen et al. Heritage Science (2015) 3:9 Page 2 of 9
numbered P201.061 to P210.036 for archiving. They
were then mounted as cross-sections (C87.129 to
C90.158) in order to be analyzed. The cross-sections
were prepared by embedding the samples between
acrylic resin cubes. The bulk sample was first fixed
to a 1 cm
3
poly(methyl methacrylate) cube using a
white PVA glue, after which the acrylic copolymer
resin (Spofacryl®, Spofa Dental CZ-10031, Prague)
was poured on the sample and the second cube
placed on top. The cross-sections thus obtained
were left to dry, then polished with water until the
sample surface was nearly exposed. Then, polishing
was continued in set circumstances using Micro
Mesh© polishing cloths in a sequence of grits (2400,
4000, 6000 and 8000 mesh) leading to a mirror-like
surface. In the case of the reference samples, a
JEOL Cross Section Polisher IB-09010CP (JEOL,
Tokyo, Japan) was used for 12 hours with a
4.0 kV accelerating voltage, 4.4 argon gas flow
and a swinging stage. The cross-sections were
photographed with an optical microscope Axio
Imager 2 (Carl Zeiss, Oberkochen, Germany) under
visible and ultraviolet light (excitation bandpass filter
from 390 to 420 nm) with magnifications up to 500x.
Reference samples used in this study were the
natural orpiment (Kremer Pigmente GmbH & Co,
Aichstetten, Germany) and laboratory-prepared
arsenic sulfide glass. The latter was synthesized by
mixing arsenic trioxide with sulfur (1:1) in a glass
tube and heating it for a few minutes over a Bunsen
burner as described by Rötter [2]. After grinding, a
fraction of the material was mixed with Arabic gum
(2/3 in water) until a good consistency was reached.
It was then applied on a calcium carbonate coated
board before being mounted as a cross-section;
other material was kept loose for PLM analysis.
–Methods and instrumentation
SEM-EDX
SEM analyses (backscattered electron images, elemental
mapping and point analyses) were carried out on gold-
coated (SPI-MODULE™Sputter Coater, SPI, West Chester,
PA, USA) cross-sections using a JEOL JSM6300 scanning
electron microscope (JEOL, Tokyo, Japan) equipped with
Pentafet Si(Li) and BSE (Tetra Link) X-ray detectors, both
from Oxford Instruments. EDX-analyses were run at an
acceleration voltage of 15 kV and a working distance of
15 mm. Data was collected using the INCA software sys-
tem, v. 4.06 (Oxford Instruments).
Micro-Raman spectrometry (MRS)
Micro-Raman spectra were acquired with a Renishaw
inVia multiple laser dispersive Raman spectrometer with
a Peltier-cooled (203 K), near-infrared enhanced, deep-
depletion CCD detector (576 × 384 pixels) using a high-
power diode laser (Toptica Photonics XTRA, Graefelfing
(Munich), Germany) operating at 785 nm in combin-
ation with a 1200 l/mm grating. Based on the particle
size, samples were analyzed using either the 50x or 100x
objectives in a direct-coupled Leica DMLM microscope
with enclosure. To avoid degradation or heat induced
physical changes, the power on the samples was reduced
to 1 mW with neutral density filters. Integration times
of 30 seconds and 5 accumulations were employed; this
resulted in an adequate signal-to-noise ratio. Spectra
were acquired using the Wire 2 Raman software and
were subsequently baseline corrected when necessary.
PLM
PLM was carried out on a Zeiss Axio Imager 2 microscope
(Carl Zeiss, Oberkochen, Germany) using a 50x or 100x
objective. Samples were dispersed and mounted in Canada
balsam (n = 1.55) and observed in slightly polarized or
cross-polarized light.
Figure 2 Cross-sectional photomicrographs of samples (a) C90.065 and (b) C90.101 under ultraviolet illumination. C90.065 clearly
shows color-modified pigment particles in the upper part of the vermilion layer (darkening) while C90.101 does not exhibit any sign of
color-changed pigments.
Vermeulen et al. Heritage Science (2015) 3:9 Page 3 of 9
Results and discussion
Due to the complexity of the sampling and despite the
many samples that were taken/studied, only three samples
will be discussed here. They are representative of the ar-
senic sulfide found and the different techniques in which
it was used: samples C90.058 and P210.011 (loose mater-
ial) are representative for arsenic sulfide mixed with ultra-
marine blue, bound with protein-based medium and used
as underlayer; sample C90.094 (P209.066) corresponds to
arsenic sulfide mixed with Prussian blue, used in finishing
layers in an urushi-containing oil medium
b
; finally, sample
C90.101 (P209.074) features unmixed arsenic sulfide used
in urushi-containing finishing layers.
For each sample, the same analytical procedure was
followed: after embedding into cross-sections, the arsenic
and sulfur distribution was recorded via SEM-EDX, the
yellow particles were analyzed by means of Raman spec-
troscopy. Then, a fraction of the remaining loose sample
was dispersed in Canada balsam for PLM analysis. The
same procedure was used for the natural orpiment and
laboratory-made arsenic sulfide used as reference samples.
SEM-EDX
SEM backscattered electron images of the samples ex-
hibit irregularly shaped and sized particles (Figure 3a, b
and c). The high-Z particles have both round and sharp
edges. Semi-quantitative SEM-EDX analyses have been
undertaken on these high-Z particles and in all cases
present a similar composition: sulfur (47 weight % ± 6%)
and arsenic (53 weight % ± 6%). This composition allowed
us to identify these particles as an arsenic sulfide pigment.
According to the backscattered electron images (Figure 3),
the size of those particles is rather variable and ranges
from 2 to 10 μm.
The nature of the arsenic sulfide pigment –natural orpi-
ment, artificial orpiment or arsenic sulfide glass –cannot
be determined with SEM-EDX analyses only. Nevertheless,
none of the foliated structure or mica-like appearance
characteristic for natural orpiment (Figure 4a) often de-
scribed in the literature [2,13,19,20] is observed in the
Japanese tower samples; rather, they feature a strong
resemblance to the structural pattern of the arsenic sul-
fide glass (Figure 4c) also very similar to the pigment with
conchoidal fractures reported in Grundmann et al. [3] and
confusingly reported as natural orpiment in Eastaugh et al.
[1]. This strongly suggests the use of synthetic arsenic sulfide
rather than the natural form of the pigment.
FitzHugh described the amorphous synthetic arsenic
sulfide particles prepared through wet chemistry from
thioacetamide solution round in morphology with a par-
ticle size of about 1 μm [13]. Grundmann and Rötter dif-
ferentiated the extremely homogeneous, fine (1–2μmin
diameter) bright yellow particles when obtained from a
thioacetamide solution described by FitzHugh from the
even smaller (0.1-0.4 μm) particles obtained when pre-
pared from hydrogen sulfide [3]. On the other hand,
synthetic arsenic sulfide pigment produced by the dry
process is described as being likely to be composed of
fine to medium particles [19] with an average size of
4μm depending on the grinding [21]. The dry processes
give rise to glassy arsenic sulfide cakes (Figure 4b) that
contain irregularly shaped and sized particles with con-
choidal fractures after grinding as described in the litera-
ture [3,19] and as observed in the cross-sections of the
laboratory-made g-As
x
S
x
(Figure 4c). Because the pigment
investigated in the frame of this study is an artificial ar-
senic sulfide pigment, the size, and shape of the particles
observed in Figure 3 tend to indicate a pigment obtained
from a dry rather than from a wet process.
MRS
Raman spectra show the same features in all of the three
samples discussed here: a major broad band at 337 cm
−1
with a shoulder at 362 cm
−1
(Figure 5) as well as small
bands at 234 cm
−1
and 471 cm
−1
. The band at 471 cm
−1
is always encountered but can range from small to
Figure 3 Backscattered electron images of samples (a) C90.058, (b) C90.094 and (c) C90.101. In all cross-sections, the high-Z particles have
been identified as arsenic sulfide.
Vermeulen et al. Heritage Science (2015) 3:9 Page 4 of 9
medium in intensity. It most likely corresponds to sulfur
remainders from the dry process preparation. Indeed,
when analyzed in Raman spectroscopy, sulfur has major
bands at 219 and 473 cm
−1
(Figure 6c). In that regard, the
band at 218 cm
−1
observed for sample C90.101 (Figure 5c)
can also be considered as a feature for some sulfur re-
mainder. Even though the yellow pigment in the three
cross-sections has been identified as arsenic sulfide by the
presence of arsenic and sulfur in SEM-EDX, these wave-
numbers do not correspond to the one observed for
natural orpiment (136, 154, 179, 202, 293, 311, 354,
367 (sh), 383 cm
−1
) and the observed spectra do not
match any of the references (Figure 6a). Comparison of
the spectra obtained with laboratory-synthetized arsenic
sulfide analyzed with Raman spectroscopy (Figure 6b)
shows that the pigment used is an arsenic sulfide glass.
The different ratios of As
4
S
4
monomer units in its
structure (band at 234 cm
−1
as well as the shoulder to the
main band at 360 cm
−1
) [22,23] between C90.101 (Fig-
ure 5c) and the two other cross-sections (Figure 5ab),
most likely indicates that the orpiment used has been
synthetized following different conditions. Indeed, the
Raman bands for the As
4
S
4
monomer units can give an in-
dication on the quenching temperature (Tq); the more im-
portant the intensities, the more important the quenching
temperature [22]. Here, the small bands observed for
C90.058 (a) and C90.094 (b) most likely indicate a mid-
range quenching temperature whereas the more intense
bands observed for sample C90.101 (c) would indicate a
much higher Tq. Based on the comparison of our spectra
with the ones obtained by Georgiev et al. [22], the
quenching temperature for C90.058 and C90.094 could
be around 450°C and 550°C for C90.101. According to
Bonazzi et al. [24] and Grundmann et al. [18], the As
4
S
4
Figure 4 Backscattered electron images for (a) natural orpiment reference material, (b) laboratory-made arsenic sulfide glass cake
(b) before and (c) after grinding.
Figure 5 MRS spectra for the arsenic sulfide pigment in samples (a) C90.058, (b) C90.094 and (c) C90.101, exhibiting characteristic
bands for g-As
x
S
x
(cfr. Figure 5b). The stars * indicate peaks characteristic for sulfur.
Vermeulen et al. Heritage Science (2015) 3:9 Page 5 of 9
monomer units present in the arsenic sulfide glass most
likely correspond to a mid-state between the As
4
S
4
β–
phase and the As
4
S
4
χ–phase because of broader bands
observed at 219, 235 and 245 cm
−1
than expected for the
more molecular ordered realgar or β–phase. Even
though Raman spectroscopy was very helpful for identify-
ing the type of arsenic sulfide used in the decorative
panels of the Japanese tower as arsenic sulfide glass, this
technique does not provide any information on the start-
ing materials.
PLM
Polarized Light Microscopy can provide information about
the starting materials. Thorough investigation of the shapes
and interference colors as well as comparison with refer-
ence materials are very helpful in this regard [2,17,19]. In-
deed, natural orpiment crystals have a pronounced layer
lattice with angular and lamellar-foliated morphology [1].
They show anisotropy effects and green to blue interfer-
ence colors when observed under slightly polarized to
cross polar light (Figure 7a) [19]. On the other hand, due
to its isotropic characteristic Arsenic sulfide glass does
not show these interference colors and varies from bright
yellow to dark when working under crossed polarizers
(Figure 7b). The internal light reflection within this ma-
terial leads to an image showing a spherical yellow par-
ticle with a dark cross in the middle (top right corner of
Figure 7b) [2].
Thorough investigation under microscope of the three
selected samples did not reveal particles with interfer-
ence colors; rather, spherical particles with distinctive
features of arsenic sulfide glass comparable to the one found
in literature - dark center, round edges, bright yellow/dark
brown/yellow areas, conchoidal fractures [3,19] - were ob-
served (Figure 8). This most likely indicates that no
natural orpiment was used as a starting material for the
Figure 6 MRS reference spectra for (a) natural orpiment, (b) laboratory-synthetized arsenic sulfide glass (g-As
x
S
x
) and (c) sulfur.
Figure 7 Polarized light photomicrographs of (a) natural orpiment and (b) laboratory-synthetized arsenic sulfide glass (g-As
x
S
x
) under
non-polarized and crossed-polarizer illumination.
Vermeulen et al. Heritage Science (2015) 3:9 Page 6 of 9
synthesis of the pigment, since otherwise grains of this
material would have been found in the thin section [21].
Compressed corners and edges resulting from crushing
round particles can give information on the brittle de-
formation structures. These structures can be observed in
Figure 8b and c. In this case, the deformations are either
due to the pigment preparation before use or to the sam-
ple preparation for PLM analysis. PLM photomicrographs
of the selected samples strongly suggest the use of arsenic
sulfide glass synthetized from arsenic oxide and sulfur as
described by Grundmann and Rötter [3].
Conclusion
Scanning Electron microscopy coupled with an EDX de-
tector, Micro- Raman spectroscopy and polarized light
microscopy have been used as part of a multi technique
approach to identify the arsenic sulfide pigment(s) used
in the decorative panels of the Japanese tower in Laeken,
Belgium. Table 1 is a summary of the results obtained
from the representative samples discussed here and from
the reference materials. Based on the size and shape of
the particles (SEM-EDX data), the wavenumber and
spectrum profile obtained in Raman spectroscopy as well
as the optical properties of the pigments in PLM, the
arsenic sulfide that was employed, could be identified
as arsenic sulfide glass (g-As
x
S
x
). This material was
synthesized from arsenic trioxide and sulfur as suggested
by the sulfur remainders detected in Raman spectroscopy.
No remainders of natural orpiment were found during the
thorough microscopic investigation of the three samples.
Figure 8 Polarized light microphotographs of (a) P210.011, (b) P209.066 and (c) P209.074 under non-polarized and cross-polar illumination.
Table 1 Recapitulative table for the two reference materials and the 3 representative types of arsenic sulfide/
techniques found in the decorative panels of the Japanese tower in Laeken, Belgium
Natural orpiment Kremer g-As
x
S
x
laboratory-made
C90.058/
P210.011
C90.094/
P209.066
C90.101/
P209.073
Particle shape - Thin and elongated forms Various shapes from
spherical to sharp-edged
- Round to elliptical-shaped particles
- Laminated masses or granular and powdery
with a fibrous structure (Figure 4a)
- Spherule can be smooth and round
(Figure 4c) - Both round and sharp edges
- Irregular sizes
- No smooth and round structures - Figure 3
Raman wavenumbers 136, 154, 179, 202, 293, 311, 354,
367 (sh), 383 cm
−1
220, 235, 339, 367 (sh),
473 cm
−1
234, 337, 362 (sh),
471 cm
−1
218, 234, 337, 362 (sh),
471 cm
−1
(Figure 6a) (Figure 6b) (Figure 5a, b) (Figure 5c)
PLM characteristics - Birefringent - Strong refraction - Isotropic and amorphous
- Anisotropic - Isotropic and amorphous - No interference colors
- Bright pink and green to blue
interference colors
- No interference colors - Full extinction
- Compressed corners and edges resulting
from crushing spherical particles
- Roundish morphology
- Foliated, micaceous structure
- Brittle, jagged
fracture behavior
- Figure 8- Ductile when exposed to mechanical strain
- Figure 7b- Figure 7a
Vermeulen et al. Heritage Science (2015) 3:9 Page 7 of 9
This absence strongly suggests that another material than
natural orpiment was used as a starting material in the
synthesis of the arsenic sulfide glass.
Different band ratios in the As
4
S
4
monomer units (as
suggested by the relative intensities of the Raman bands at
234 and 362 cm
−1
) tend to show that the different g-As
x
S
x
used in the various panels were manufactured in different
batches and were quenched at different temperatures. The
more intense the bands for the As
4
S
4
monomer units are,
the higher was the quenching temperature.
Now that the arsenic sulfide pigment found in the dec-
orative panels of the Japanese tower has been identified
as arsenic sulfide glass synthesized from arsenic trioxide
and sulfur, further investigations will be conducted in
order to investigate stability of the different forms of ar-
senic sulfide glass and the influence of media [25] and en-
vironmental factors on its degradation.
Only hypotheses can be formulated at this stage of the
study. As mentioned by Grundmann and Richter [17],
the artificial arsenic sulfide glass might have been intro-
duced in order to replace the very light sensitive natural
pigment. In that regard, the glassy nature of the studied
pigment could be the origin of its unusual stability. An-
other factor determining the stability of a pigment can
be its use in a lacquer-containing layer in which the pig-
ment is embedded. The lacquer-containing binder might
also protect the pigment from oxidation and light due to
its high stability.
Endnotes
a
The unpublished report of this study is archived at
KIK-IRPA under the number 2010.10826.
b
Samples analyzed by py-GCMS (Thermo, Waltham,
MA, USA) with TMAH 2.5% in MeOH and pyrolyzed at
550°C for 12 sec. Detailed procedure and results can be
found in the unpublished report of this study archived at
KIK-IRPA under the number 2010.10826.
Competing interests
The authors declare that they have no competing interests.
Authors’contributions
The analyses and interpretation of the results were carried out by MV and
coordinated by JS. MV wrote the first draft of the manuscript, that was
revised by JS and, finally, by KJ. All authors read and approved the final
manuscript.
Acknowledgments
We cordially thank Günter Grundmann for his precious advice regarding PLM
and arsenic sulfide glass. This research is made possible with the support of
the Belgian Science Policy Office (BELSPO) through the research program
Science for a Sustainable Development –SDD, “Long-term role and fate of
metal-sulfides in painted works of art –S2ART”(SD/RI/04A).
Author details
1
Laboratory of polychrome artifacts, Royal Institute for Cultural Heritage, Parc
du Cinquantenaire 1, B-1000 Brussels, Belgium.
2
AXES Research Group,
Department of Chemistry, University of Antwerp, Groenenborgerlaan 171,
2020 Antwerp, Belgium.
Received: 7 October 2014 Accepted: 10 February 2015
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