X-RAY SPECTROMETRY
X-Ray Spectrom. 2008; 37: 328–337
Published online 4 March 2008 in Wiley InterScience
(www.interscience.wiley.com) DOI: 10.1002/xrs.1024
Pigment characterization and state of conservation
of an 18th century fresco in the Convent of S. António
dos Capuchos (Estremoz)
M. Gil,1,2∗ M. L. Carvalho,2 A. Seruya,1,2 I. Ribeiro,3 P. Alves,3 A. Guilherme,2 A. Cavaco,2
J. Mirão4 and A. Candeias5
1
2
3
4
5
Conservation and Restoration Department, Science and Technology Faculty, Lisbon New University, 2829-516 Caparica, Portugal
Atomic Physics Center, Lisbon University, Av. Professor Gama Pinto 2, 1649-003 Lisboa, Portugal
Institute of Museums and Conservation (IMC), Rua das Janelas Verdes 22 1300-001 Lisboa, Portugal
Geosciences Department and Geophysics Center of Évora, University of Évora, Rua Romão Ramalho 59, 7000-671 Évora, Portugal
Chemistry Department and Évora Chemistry Center, University of Évora, Rua Romão Ramalho 59, 7000-671 Évora, Portugal
Received 10 January 2008; Accepted 15 January 2008
This article describes a study carried out on a mural painting in the Convent of Santo António dos
Capuchos in the town of Estremoz (southern Portugal). Experimental work was undertaken to identify
pigments and to elicit hypothesis about their local origin. Another aim was to ascertain the painting
technique (binders, stratigraphy) and to try to investigate the causes that led to the deterioration of the
blue and green pigments.
Elemental and mineralogical analyses of the pigments were performed by x-ray diffraction
(m-XRD), portable energy dispersive x-ray fluorescence (EDXRF) and scanning electron microscopy
(SEM), complemented by microchemical tests and Fourier transform infrared spectroscopy (FTIR). These
techniques have shown that a variety of pigments were used, namely earth pigments (red and yellow
ochres, green earth and probably black earth and umber), copper pigments (azurite, malachite), probably
from the Estremoz region, and smalt, used pure or in mixtures. The results also revealed the presence of
salt veils, biological colonization and possibly secco applications with lime (lime painting), which may
have contributed to the actual state of conservation of fresco. Copyright  2008 John Wiley & Sons, Ltd.
INTRODUCTION
The Convent of Santo António dos Capuchos in the town
of Estremoz was built in 1654 and served two ecclesiastical
orders, S. António and Nossa Sra do Monte da Virgem,
before becoming extinct in 1834. The extinction accelerated
the decay and vandalization of the building, especially after
1910, a period in which the church was profaned and the
altars destroyed. Afterwards, the building was used as a
cork factory and barn. Nowadays, the convent is closed to
the public, is in an advanced state of ruin and is surrounded,
since 1890, by the town’s public cemetery.1
The fresco, measuring 4.80 ð 4.92 m, occupies the entire
altar wall of a small quadrangular chapel and is a testimony
to the rich mural painting produced in the Alentejo
region. The composition, characteristic of the 18th century
Barroc style, presents Solomonic columns, volutes, exuberant
flower ornamentation, two faint side niches with devotional
figures—S. Archbishop and S. Francis of Assisi—and
Calvary1 in the central panel.
The painting seems to be left unfinished and has visible
marks of interventions probably due to the removal of the
Ł Correspondence
to: M. Gil, Conservation Restauration Centro de
Fı́sica Atómica da Universidade de Lisboa Faculdade de Ciências
Av. Prof. Gama Pinto 2, 1649-003, Lisboa, Portugal.
E-mail: [email protected]
Copyright  2008 John Wiley & Sons, Ltd.
wooden sculpture of Jesus on the cross. Other enigmatic
small holes are still present in the external Solomonic
columns. From the existent lacunae in the painting, one
can see that it was executed after the application of three
layers of mortar over the original wall. A scratch in the
mortar is visible all along the borders of the central panel.
Its regularity and the small elevation of some of the borders
seem to indicate the presence of a structure at the time
of their application. The paintings do not present signs of
ulterior restoration interventions, except in the sky of the
Calvary scene that could have very small repainted areas.
Many lacunae in the chromatic layer, especially in the blue
and green pigments, can be seen.
Yellow and red colors dominate the palette. The origin
of these pigments is unknown. There are almost no
historical data available about commercial trade concerning
pigments between Portugal and abroad, and are even less
within Portuguese territory. However, it is known by some
famous treatises, such as Plinio’s (1st BC), Pedro Nunes’s
(16th century), Francisco Pacheco’s (17th century) and later
mineral reports (18th/19th century), that Portugal had red
and yellow earths and clays which could have been applied
in paintings.2
Particularly significant is the fact that the Estremoz region
is geologically rich in pigment raw materials—ochres from
schist weathering, terras rossas (ochres from weathering of
Study of pigments used in an 18th century Portuguese fresco
carbonate rocks) and ochres, malachite and azurite from
copper ore mines—that could have been used as pictorial
materials. Ochre raw materials were cheap materials,
normally easy to extract from nature and to prepare
for painting purposes. In the Alentejo region, they were
used until 50–60 years ago in traditional homemade limewashings.3 So there is a hypothesis that the artists who
made the painting of S. António dos Capuchos could have
benefited from local natural resources.
EXPERIMENTAL
Microscopical, chemical and analytical techniques were
applied to identify all mineral species present, so as to provide information about painting techniques (stratigraphy),
and these techniques were applied in the case of the blue and
green layers to detect any organic binder that might indicate
a secco technique (tempera). Another aim of the analyses
performed was to hypothesize the origin of the pigments.
Sampling
In situ analyses were performed by energy dispersive x-ray
fluorescence (EDXRF) on 43 spots, and additionally, 26
microsamples were taken in order to carry out crosssection and chemical analysis. Figure 1 presents the sample
locations in the painting, studied by EDXRF, Fourier
transform infrared (FTIR), scanning electron microscopy
(SEM), x-ray diffraction (-XRD) microscopic techniques and
microchemical tests.
Figure 2. Portable EDXRF spectrometer.
of the corresponding photographic documentation were
carried out in reflected light configuration, after enclosing
the polished sections in polyester resin Epofix Fix (25 parts
of resin to 3 parts of hardener by weight). Microchemical
spot tests were applied to pigment analysis by the use of
different reagents following a dichotomic grid for each color.
Pigment discrimination was achieved as described by Joice
Plester.4
The elemental composition was obtained in situ by an
EDXRF portable equipment (Fig. 2) using an Amptek x-ray
source Eclipse II (operated at 25 kV and 50 µA) with a
Analytical techniques
The optical microscopy observations and the production
of the corresponding photographic documentation were
obtained by a stereomicroscope Leitz-Wetzler equipped with
a Leica DC500-2002 photo camera, with 65ð, 110ð and
220ð magnifications. The observations and the production
Figure 1. Sample locations and analytical technique used
(EDXRF, FTIR, DRX, optical microscopy and microchemical
analysis).
Copyright  2008 John Wiley & Sons, Ltd.
Figure 3. Details of the painting and optical micrograph of a
red (a) and yellow (b) layer cross-sections. It is generally
accepted that iron oxides are the phases responsible for ochre
color. Of them, hematite (˛-Fe2O3) and goethite (FeO(OH))
configure iron as the main chromophore for red and yellow,
respectively. However, these two phases, in the red and
special yellow layers, are hardly perceptible probably due to
the manufacturing process of these pigments.
X-Ray Spectrom. 2008; 37: 328–337
DOI: 10.1002/xrs
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M. Gil et al.
Figure 4. EDXRF spectrum of the brown sample ecsac034 (b) and optical micrograph of a brown layer cross-section (a). In reflected
light microscopy, it can be distinguished as black and opaque or weakly translucent brown particles. Other phases are less visible.
tantalum disc collimator, so that the x-ray beam had a 2 mm
diameter, and the anode material used was Ag. The detector
was an Amptek model XR-100CR with an effective area of
7 mm2 , a detector diode, a thickness of 300 µm and a Be
window of 12.5 µm thickness. In order to easily adjust the
sample position at a fixed distance of 7 mm from the tube and
detector, there are two point lasers mounted on the tube and
detector holder. However, this fixed position was not always
achieved due to impracticalities imposed by the tripod, or
even due to a barely reachable pigment on the wall. The
angle between the incident beam and emitted beam from the
sample is arranged at 90° .5 – 8
The spectra were collected using the software provided
with the detector. The calibration of this software was
performed with a variable radioactive source using the K
series energies of four different elements: copper, rubidium,
molybdenum and silver. The spectra were analyzed using
WinQxas program.
One must note that in the EDXRF analysis there were no
critical instrumental characteristic lines added to the sample
characteristic emission lines. This kind of possibility was
tested by means of the pure dispersion spectrum of this
system.
The -XRD was performed on a Bruker AXS powder
diffractometer, model D8 Discover, using Cu K˛ radiation.
The step size used was 0.02° (within the angular range from
2.2° to 67.6° ). The step time was 1 s. The EVA code was used
for the identification of the peaks.
Copyright  2008 John Wiley & Sons, Ltd.
The transmission IR spectra were recorded using an FTIR
Perkin Elmer Paragon 1000 PC spectrophotometer. Twentyfive signal-average scans were acquired on the samples. The
KBr (IR grade, Merck, Germany) disks of powdered pigment
samples were examined in the region 4000–400 cm1 at a
resolution of 4 cm1 . To prepare the samples, 1–2 mg of
pigment was mixed homogenously with anhydrous KBr in
an agate mortar. A pressure of 10 tonnes was applied to this
mixture in order to obtain transparent disks. Identification
was based on comparing the bands of the recorded FTIR
spectra with those of reference materials, and from library
spectra.
Finally, SEM investigation was carried out using a Hitachi
S-2400 SEM equipped with a Rontec standard x-ray energydispersive spectrometer. The samples were coated with a
thin conductive film of gold. The high voltage applied was
25 kV.
RESULTS
The nature of pigments
Reds and yellows (Fig. 3(a) and (b)) are the dominant colors
and can be identified on the architectural backgrounds
(niches) in the sun and flower decorations on the upper panel
(Fig. 1). In situ EDXRF analyses of the red colors revealed
high abundance of chalcophile chemical elements, namely
Cu C Zn, and also Pb and As, suggesting that most of the reds
were probably ochres from alteration caps of nearby copper
X-Ray Spectrom. 2008; 37: 328–337
DOI: 10.1002/xrs
Sample
ecsac003
ecsac004
ecsac016
ecsac017
ecsac018
ecsac019
ecsac020
ecsac012
ecsac025
ecsac037
ecsac038
ecsac007
ecsac030
ecsac034
ecsac010
ecsac002
ecsac008
ecsac015
ecsac023
ecsac029
ecsac031
Location
Right panel
Right panel
Central panel
Central panel
Central panel
Central panel
Central panel
Central panel
Left panel
Left panel
Left panel
Right panel
Left panel
Left panel
Right panel
Right panel
Right panel
Central panel
Central panel
Left panel
Left panel
Copyright  2008 John Wiley & Sons, Ltd.
Red
Red
Red
Red
Dark red
Red
Red
Dark red
Red
Red
Red
Orange-red
Orange
Brown
Brown
Yellow
Yellow
Yellow
Yellow
Yellow
Yellow
Color
4 410
4 200
3 510
4 460
2 690
2 325
4 360
2 120
3 160
2 180
2 370
870
2 370
2 075
660
1 480
1 250
4 020
6 160
2 930
2 340
Si
4 550
3 100
1 620
2 600
1 670
1 840
1 760
800
2 500
1 560
1 380
—
2 740
2 290
—
1 000
850
2 660
4 470
2 950
2 500
S
28 200
22 570
21 125
19 700
17 900
19 420
16 640
18 900
20 430
1 800
20 300
10 000
19 430
20 000
9 220
8 630
11 900
19 200
21 200
21 640
19 550
K
480 900
395 000
222 300
268 000
231 300
261 300
169 400
211 950
289 800
211 450
246 550
97 750
274 400
301 600
75 350
122 440
108 200
335 700
271 850
330 800
238 000
Ca
850
—
—
680
—
710
430
1 650
220
770
316
—
600
600
720
940
1 195
1 080
230
490
Ti
1 330
1 380
1 640
3 590
8 520
1 250
2 380
5 890
1 655
730
1 590
370
1 580
20 400
3 070
970
1 000
1 545
1 250
2 525
1 925
Mn
Table 1. Peak intensity (š10%) obtained by EDXRF for the red, orange, brown and yellow pigments
48 700
70 200
90 850
66 360
399 500
40 300
52 230
281 750
60 680
16 630
51 740
15 310
90 390
118 670
19 140
35 180
39 090
44 720
67 720
116 500
92 850
Fe
—
—
—
—
—
—
9 480
—
—
—
—
—
—
—
—
—
—
—
—
—
—
Co
—
—
—
6 610
—
—
5 500
—
—
—
—
—
—
—
—
—
240
—
—
—
—
Ni
—
1 280
30
10 560
1 950
1 965
2 180
370
—
1 100
500
—
730
515
315
210
340
—
500
—
—
Cu
1 170
1 320
670
4 300
1 080
—
2 290
600
1 050
—
—
390
400
—
370
285
650
1 160
485
—
—
Zn
—
—
—
17 600
—
—
21 650
4 425
1 650
—
—
—
—
—
—
—
—
—
—
—
—
As
Ba
—
—
—
—
—
800
—
—
—
1 900
—
290
—
—
—
1 280
370
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
290
—
—
—
—
—
Sr
4 500
2 350
—
—
—
—
—
—
—
—
—
—
—
—
—
—
250
—
—
—
—
Pb
Study of pigments used in an 18th century Portuguese fresco
X-Ray Spectrom. 2008; 37: 328–337
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M. Gil et al.
ore mines (Table 1). Particularly, the Mostardeira mine, in
the vicinity of Estremoz, could be a probable source of these
pigments. This copper mine, in the past, was a well-known
local source of red clay for pottery painting9 and its ochres
are clearly enriched in As.
The two samples (ecsac018 and ecsac012), corresponding
to darker reds, show higher amounts of Fe and Mn.
Manganese oxides are black or brown, thus rendering, due
to their chromophore contribution, a stronger or weaker
brownish hue to the pigment’s final color.10
The low amounts of Cu, Zn, Pb and As indicate that the
yellow pigments, unlike the reds, may have a terrigenous
source, specially for samples ecsac029 and ecsac031, in which
these elements are absent (Table 1). However, in the other
four samples, one cannot exclude the contribution of sediments from alteration of sulfide ores present in the region.
The orange hues can be found in natural ochres, but the
intermediate values of Cu and Zn may also indicate that
a mixture of yellow and red ochres could have been used
(Table 1 and Fig. 8).
In the case of browns, the high amount of Mn in sample
ecsac034 may indicate an intentional addition of pirolusite.
Nevertheless, one cannot exclude the use of natural umber
earth pigments. Geologically, umbers are very fine grained
sedimentary rocks composed of manganese hydroxides and
oxides (primarily the minerals manganite and pyrolusite).
As natural materials, these are not pure substances and
other minerals may be present.10 This fact could explain
the presence of other elements (e.g. Si, S, K, Ca, Ti, Fe,
Cu and Zn) found in the two brown samples analyzed
and the differences in composition between them (Table 1).
The reflected light-observable opaque particles seem to be
manganese oxides and hydroxides due to their black or very
dark brown and weak translucency (Fig. 4).
A high amount of Mn (which is indicative of the presence
of pirolusite, MnO2 ) is also present in two black samples.
Figure 5. Optical micrograph of blue layers: azurite (a), smalt (b) and -XRD pattern (c). Smalt is easily distinguished from azurite by
its color and by its elongated sharp particles with fractured edges visible. The coarse-grained particles of azurite present greenish
overtones, which indicate alteration to malachite.8
Table 2. Peak intensity (š10%) obtained by EDXRF for the blue pigments
Intensity (pick area)
Location
Sample
Si
S
K
Left panel
Left panel
Left panel
Left panel
Left panel
Central panel
Central panel
ecsac026
ecsac027
ecsac028
ecsac032
ecsac036
ecsac041
ecsac043
5 340
6 380
2 500
7 680
1 800
3 400
1 640
1 200
3 200
1 590
2 400
—
2 790
890
14 700
13 480
12 800
20 900
17 790
22 200
11 100
Copyright  2008 John Wiley & Sons, Ltd.
Ca
Ti
Cr
96 120
800 —
53 170
600 —
139 700 1 000 700
209 700
900 —
223 860
100 —
325 000
645 —
84 270
540 —
Mn
Fe
Co
3 500
1 970
2 790
2 460
2 060
1 255
3 210
55 600
45 330
35 600
41 130
45 390
14 850
42 500
35 580
30 900
5 900
23 080
—
2 555
26 060
Ni
Cu
Zn
As
Ba
Pb
17 500
4 485 4 220 87 300 — 2 100
14 180
2 255 2 160 83 430 —
830
3 780
—
—
14 170 —
—
10 625
3 700 3 100 46 420 250 —
—
211 150 —
1 420 —
—
2 340
—
600 5 465 —
—
13 380
4 630 —
65 500 — 2 800
X-Ray Spectrom. 2008; 37: 328–337
DOI: 10.1002/xrs
Study of pigments used in an 18th century Portuguese fresco
These pigments probably came from black earths formed in
oxidizing sedimentary environments, but it can also be due
to burnt umber. In four microsamples taken, microchemistry
tests have detected the presence of phosphates, which are
normally attributed to bone black.
The results of EDXRF (Table 2) and -XRD show that two
types of blue pigments were used (Fig. 5(a) and (b)). A sample
of ecsac036 shows a higher Cu content and absence of Co or
Ni, suggesting that azurite (the blue copper basic carbonate
Cu3 CO3 2 .OH2 ) was the pigment used. Nevertheless, by
-XRD (Fig. 5(c)) only malachite was found, due probably
to the fact that azurite tends to turn into malachite when
exposed to air.11 Samples ecsac028 and ecsac041 show high
values of Co, Ni and As, and absence of Cu, indicating
that the pigment applied was smalt (cobalt-doped glass).
Samples ecsac026, ecsac027, ecsac032 and ecsac043 indicate
the presence of Co, Ni and Cu, suggesting that a mixture
of azurite and smalt was used. This was also possible to
observe by cross-section analyses in which two types of blue
pigments with different morphologies were identified. Smalt
is easily recognized by its coarse elongated sharp particles
with visible fractured edges (Fig. 5(b)).10
The presence of As and Ni are due to the fact that these
elements are common in cobalt ore minerals, such as cobaltite
((Co,Fe)AsS) or smaltite ((Co,Ni)As3 – 2 ),12 which were used
to obtain CoO in the preparation of smalt glass in Europe
since the Middle Ages.12 During the metallurgical process,
As would tend to volatilize, and therefore, the high content of
this element may be understood as a result of an incomplete
industrial process.
In the manufacture of smalt, cobalt ore is roasted and the
cobalt oxide (CoO) thereby obtained is melted together with
quartz (SiO2 ) and potash (K2 O) or added to molten glass. The
presence of Fe in all the samples can result from the cobalt
ore used or possibly from the red ochre layers underneath or
near the area analyzed.
Smalt was used extensively for the background of the
decoration in the upper panel. There are also traces of this
pigment in the sky area of the central panel, in the garments
of the Virgin and in one of the Solomonic columns (Fig. 1).
Remains of azurite have only been found in some details of
the architectural and floral decoration in the lateral panels.
The origin of the smalt could have been somehow tied to
the products of glazed pottery manufacture in the town of
Estremoz.
As for the green colors, the high EDXRF Cu yield (Table 3)
indicate that the pigment used was malachite (basic copper
carbonate Cu2 CO3 .OH2 ). This is corroborated by the XRD results (Fig. 6) and by the presence of Zn, which usually
accompanies Cu in carbonates from alteration caps of copper
ores. Three of the samples (ecsac042, ecsac033 and ecsac013)
show slightly lower intensities of Cu, which accompanied
Figure 6. Optical micrograph of a green layer cross-section (a) and XRD pattern of malachite C green earth (b). Strong green
polycrystalline particles of celadonite are clearly distinguished. Malachite particles are more translucent with blue-green overtones.
Copyright  2008 John Wiley & Sons, Ltd.
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M. Gil et al.
Table 3. Peak intensity (š10%) obtained by EDXRF for the green pigments
Intensity (pick area)
Location
Sample
Right panel
ecsac009
Central panel ecsac011
Central panel ecsac013
Central panel ecsac021
Left panel
ecsac024
Left panel
ecsac033
Left panel
ecsac035
Central panel ecsac042
Si
S
K
Ca
Ti
Cr
Mn
6 120
4 235
2 860
3 080
1 130
2 820
3 530
3 455
3 130
1 490
2 230
1 300
860
2 200
1 700
3 300
37 400
32 750
21 390
20 520
14 680
21 100
24 060
21 800
262 250
153 080
248 000
103 800
118 700
245 060
250 400
250 300
700
640
190
870
70
400
670
955
—
—
640
860
—
—
—
—
4 260
7 390
600
2 600
775
2 320
2 920
1 920
Fe
Ni
206 860 —
320 790 —
21 670 —
150 000 —
33 090 300
67 990 —
85 300 —
79 020 —
Cu
Sr
29 580 —
23 620 300
3 450 —
16 110 —
16 700 —
4 900 —
78 900 —
1 480 —
Zn
As
Pb
2 155
—
600
1 540
790
—
—
—
1 200
—
—
—
—
—
—
—
—
1 090
—
1 385
—
—
—
—
by a high Ca yield may indicate lower pigment/binder ratio
used or a thinner paint layer that increases the volume of
the ground calcium carbonate analyzed. The higher counts
of K and Fe observed in some cases (especially in samples
ecsac009, ecsac011, and ecsac021) and the -XRD results
(Fig. 6(b)) indicate the concomitant use of malachite and
celadonite (K [(Al,FeIII),(FeII,Mg)]AlSi3 , Si4 O10 OH2 ), and
hence, reveal that green earth pigments were also used
(Table 3 and Fig. 6(a) and (b)).
Painting technique and state of conservation
The painting technique was very simple, with most areas
of the decoration applied with layers of a single pigment.
A variety of pigments were used as shown by the results
described above. These consisted of red and yellow ochres,
probably black earths and umber, bone black, malachite,
azurite, smalt and green earth. The palette of the scheme
was extended by mixing (possible some oranges, greens and
blues) and layering the pigments in the light, shadows or
in the architectural decorative motifs to achieve different
hues within the same color, as well as a variety of chromatic
effects (Figs 6, 7 and 8). The dominant colors were easy
to obtain and handle because they were mineral earth
pigments. Probably for reasons of economy, malachite and
azurite, which were more expensive pigments, were mostly
used in conjunction with green earth (greens in general) and
Figure 7. Optical micrograph of blue layer cross-section
(Solomonic columns) where particles of smalt and azurite are
visible below a thin layer of ochre pigment.
Copyright  2008 John Wiley & Sons, Ltd.
Figure 8. Example of mixing pigments (green C orange). From
the dark green hue of the particles it seems that it was green
earth that was added. Optical observation was unable to reveal
if the orange is a result of a mixture of yellow and red ochres or
is a natural orange ochre.
smalt (blues in the Solomonic columns), respectively. As pure
pigment, azurite seems to have been used only as a finishing,
probably already a secco. Also, the extensive lacunae areas
in the blue and green pigments raised the possibility of a
secco technique (tempera). Nevertheless, FTIR analyses were
not conclusive due to a series of interfering factors (e.g. the
presence of the aerial lime magnesium mortar matrix and
biological colonization). No clear evidence of organic binders
except lime was found (Fig. 9(a) and (b)). Lime painting is
another secco technique that is normally found in finishing
details (e.g. highlights). It consists in applying the pigments
mixed with lime (water or milk) on a dry surface that may or
may not have been previously wetted. It could have been an
option in this case.
Observations with SEM revealed biological colonization
and some deterioration of the lime matrix (Fig. 10). The
actual state of conservation can be explained by the presence
of whitish salt veils, probably from the recrystallization of
calcium and magnesium carbonates from the mortar detected
by the naked eye, and within the chromatic layer by SEM. But
the possible lime secco application of azurite, malachite and
green earth cannot be dismissed. Applied to a dry mortar,
these layers are liable to flake off and are much less durable.
Finally, smalt has also a reputation for being difficult to work
X-Ray Spectrom. 2008; 37: 328–337
DOI: 10.1002/xrs
Study of pigments used in an 18th century Portuguese fresco
Figure 9. FTIR spectra of blue (a) and green (b) paint layers. The presence of calcium carbonate is identified by the combination
bands at 2514 and 1798 cm1 , elongation band C–O at 1427 cm1 and deformation bands (O–C–O) at 874 and 712 cm1 .
Elongation band C–H at 2983 and 2875 cm1 could reveal the presence of organic material. Nevertheless, these bands can also
appear naturally to the reference spectra of calcium carbonate.
with and to fade due to Co and K lixiviation from the glass
matrix.11
Significant passages of underdrawing are visible in the
four painting panels due to the high level of deterioration
and due to the fact that this painting seems to have been left
unfinished. The painting was executed in an upper dolomitic
aerial lime plaster layer, with approximately 1 mm thickness.
The slaked lime was probably obtained by calcination of
dolomites, from regional quarries. Once the plaster was
applied, the architectural scheme was planned. First, the
wall space was divided into sections with the help of a
snapping rope while the mortar was still fresh. Then, in the
upper part that was the first to be painted (due to the presence
of a pontata), the contours of the two angels were incised,
while in the lower parts, the figures were first outlined with
black pigment. Tools such as ropes, triangles (with different
angles) and rulers were used to make straight lines, circles
and arcs. In terms of the painting execution, although the
stylistic quality of the central panel is clearly poorer than the
lateral panels, there are not enough evidences to affirm that
different hands made them.
Copyright  2008 John Wiley & Sons, Ltd.
CONCLUSIONS
Conservation requires a critical approach based on the
definition of the main characteristics of the object to be
dealt with. For paintings, a correct physical and chemical
characterization of pigments is crucial for their appropriate
appreciation.
There are still few systematic studies done in the mural
paintings from the 16th to 18th century in the Alentejo region
that allows one to make comparisons and conclude about
technical options and materials that were used in southern
Portugal. This study has provided important data on the
painting of Santo António dos Capuchos.
It revealed a range of solutions that were taken concerning the pigments and painting techniques, especially in the
cases of the blue and green color, probably for overcoming
economical issues. Elemental and mineralogical compositions reveal some possible geological sources of the pigments.
It is impossible to be certain that some of the local geological
sources were used but that is a likelihood, since the raw materials are similar to those found in colorant earths from the
X-Ray Spectrom. 2008; 37: 328–337
DOI: 10.1002/xrs
335
336
M. Gil et al.
Figure 10. SEM micrograph and EDX spectrum of the recrystallization of the calcium magnesium carbonate of the mortar (left) and
lime matrix deterioration (right) possibly due to biological activity.
Estremoz region,3 especially the red ochres. The exceptions
are the green earth pigment and the smalt found. Celadonite
(green clay mineral) is a micaceous mineral typical of basalt
weathering or sedimentary basins unlikely to be found in
the metamorphic geological environment of Estremoz, and
smalt is an artificially made glass. It was not possible to
confirm that terras rossas, which are abundant materials
Copyright  2008 John Wiley & Sons, Ltd.
near the church, were used in the painting. High amounts of
calcium normally enables one to identify this type of ochre3 ;
however, in this case, the calcium carbonate matrix of the
mortar did not allow reaching such a conclusion. Finally,
SEM observations allowed further insights into the fresco
structure and painting deterioration by revealing the nature
of the whitish veils on the top of the painting layers, and
X-Ray Spectrom. 2008; 37: 328–337
DOI: 10.1002/xrs
Study of pigments used in an 18th century Portuguese fresco
deterioration of the matrix of lime mortar was probably due
to biological colonization.
Acknowledgements
The authors wish to acknowledge the Fundação para a Ciência e
Tecnologia for financial support (PhD grant SFRH/BD/1263/2003
and project POCI/HEC/59555/2004) through Program Ciência e
Inovação 2010 (POCI2010) cofinanced by the EU trust FEDER. The
authors wish to thank the collaboration in this project provided by
the expertise of the professional photographer Manuel Ribeiro and
of Dr Machado de Leite (INETI).
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