JOURNAL OF RAMAN SPECTROSCOPY
J. Raman Spectrosc. 31, 407–413 (2000)
Raman spectroscopic studies of a 13th
century polychrome statue: identification
of a ‘forgotten’ pigment
H. G. M. Edwards,1 * D. W. Farwell,1 E. M. Newton,1 F. Rull Perez2 and S. Jorge Villar3
1
Chemical and Forensic Sciences, University of Bradford, Bradford BD7 1DP, UK
Cristalografia y Mineralogia, Facultad de Ciencias, Universidad de Valladolid, Prado de la Magdalena S/N, 47011 Valladolid,
Spain
3
Area de Geodinamica, Facultad de Humanidades y Educacion, Universidad de Burgos, Calle Villadiego S/N, 09006 Burgos,
Spain
2
A Raman microscopic analysis of pigments applied to a 13th century polychrome stone statue of Santa Ana
in Santa Maria la Real, Sasamon, Spain, has successfully identified the materials used. The spectral analysis
reveals that the stone substrate had been treated with gypsum prior to the application of the pigments.
The use of cinnabar, mercury(II) sulfide, in admixture with lead(II) lead(IV) oxide (minium), is a feature of
interest; the presence of calcite in the cinnabar could point to a local mineralogical source. The presence of
organic compounds in the pigments analysed suggests their use as binding agents or surface varnishes for
protection or enhancement of the appearance of the statue. The use of ‘mosaic gold’, tin(IV) sulfide, in place
of gold on the hem of the cape, identified by Raman spectroscopy and confirmed by SEM points to the use
of a forgotten technology. Our results also suggest a spectroscopic protocol for the identification of tin(IV)
sulfide in ancient pigment mixtures in the presence of other sulfide pigments such as orpiment, realgar and
cinnabar. Copyright  2000 John Wiley & Sons, Ltd.
INTRODUCTION
The use of Raman spectroscopy as a technique for
the characterization of mineral pigments on historiated
manuscripts and wall-paintings has been demonstrated for
several scenarios.1 – 5 A major difference in the information
provided from these sources arises from the conditions
under which the artefacts have been preserved. Generally,
historiated manuscripts have been maintained in scriptoria,
libraries and museums, often under controlled environments, whereas wall-paintings and frescoes have been
subjected to climatic changes and environmental damage. Atmospheric pollution in recent years is thought to
have been particularly responsible for serious deterioration of decorated monuments and artwork exposed to
the elements.6 – 9 Biodeterioration of wall-paintings and
their substrata by lichens, algae and bacteria is important where sources of nutrients are available from external
agencies, including hydrocarbon emissions from vehicle
exhausts.7,8,10,11
Despite this, wall-paintings from the Roman and mediaeval eras have survived, although sometimes only in
a fragmentary state,2,12 – 14 and vibrational Raman microscopy has been used to especially good effect in providing archaeologists and conservators with information
on ancient technologies with regard to the preparation
of pigments and substratal surfaces. The identification of
* Correspondence to: H. G. M. Edwards, Chemical and Forensic
Sciences, University of Bradford, Bradford BD7 1DP, UK; e-mail:
[email protected]
Copyright  2000 John Wiley & Sons, Ltd.
pigment mixtures has been another area of success1 – 3
in conjunction with databases constructed from visible and near-infrared excitation of Raman spectra. The
use of organic-based pigments, although identified in
manuscripts,1 is less well-substantiated for wall-paintings
where it was recognized even in antiquity that dyes
extracted from plants were fugitive.5,15,16
Hitherto, there has been no report of the Raman spectroscopic study of pigments from polychrome statuary;
this type of artefact is of great interest since it represents a class of painting which is intermediate between
manuscripts and wall-paintings. Since mediaeval times,
religious statues have been displayed in public places and
moved in procession from one site to another. Physical handling and exposure to environmental changes of
humidity and temperature often result in detachment of
pigmentation, and conservation requires knowledge of the
materials used in ancient times, i.e. pigment, binder and
substrate and their interaction. In the present work, we
report the first analysis by Raman spectroscopy of a mediaeval stone polychrome statue, viz. that of Santa Ana
from Santa Maria la Real, Sasamon, near Burgos, northern
Spain.
A description of the Santa Ana statue
An important polychrome statue of Santa Ana, mother of
the Virgin Mary, in Santa Maria la Real, Sasamon, Burgos,
Spain, is 1.65 m in height and dates from the end of the
13th century (Plates 1, 2 and 3). The Gothic figure stands
on a plinth with an inscription. Eleven small fragments
Received 15 September 1999
Accepted 5 November 1999
408
H. G. M. EDWARDS ET AL.
of paint for our analysis were taken from different parts
of the statue as follows: 1 red cape head-dress; 2 green
tunic sleeve; 3 green dress; 4 black sandal; 5 yellowbrown dress hem; 6 yellow cape hem; 7 black tunic cuff;
8 flesh pink hand; 9 grey head-dress; 10 dark red belt;
11 brown coif.
A ‘forgotten’ pigment
The ancient pigment aurum musivum, mosaic gold, featured strongly in early alchemical texts because as yellow,
crystalline tin(IV) sulfide it closely resembles gold. The
oldest European text referring to mosaic gold is an anonymous 14th century manuscript in the Biblioteca Nazionale
in Naples; the tin(IV) sulfide was prepared in the laboratory from tin amalgam, sulfur and ammonium chloride.17,18
It is clear that, although tin(IV) sulfide is precipitated on
reaction of a tin(IV) salt with hydrogen sulfide,19 the product is not suitable for artistic work as it blackens on drying,
to form a mixture of tin(IV) oxide and sulfide. Heating
a mixture of tin and sulfur produces tin(II) sulfide unless
the reaction is undertaken at high pressure, and the role of
the ammonium chloride is seen to be a vital one, probably
through the formation of an ammonium polysulfide.20
Mosaic gold was known through alchemical Chinese
texts which predate European manuscripts by over a
millennium; however, the preparation of Chinese mosaic
gold was substantially different in that ingots of tin were
heated with an alum and ammonium chloride in a sealed
iron vessel at 500 ° C for many days.21
Although popular in mediaeval and Renaissance times,
mosaic gold is rarely mentioned in modern texts devoted
to ancient pigments and their composition.15,16 Yet, yellow
pigments such as massicot, lead tin yellow types I and
II, lead antimonate yellow, orpiment, realgar and chrome
yellow are much discussed in comparison;22 it is equally
manifest that the identification of ancient pigments used
in works of art is sometimes not possible on the basis of
limited knowledge and databases currently in operation.
With this purpose, we have studied the Raman spectrum
of ‘mosaic gold’ and compared the results with the spectra
recorded here from regions of the mediaeval statue in an
attempt to identify ancient pigments.
pigment specimens from the 13th century statue required
2000 scans accumulation at 4 cm 1 operating at 1064 nm
and a nominal power of 20 mW. Spectra from other pigmented specimens were recorded over 4000 scans accumulation with a spectral resolution of 8 cm 1 and a 40ð
objective, which represents a sample ‘footprint’ of about
20 µm. Wavenumbers are accurate to š1 cm 1 and spectra
were corrected for a white light source intensity calibration.
RESULTS AND DISCUSSIONS
Good-quality Raman spectra were obtained which facilitated the identification of the pigments, pigment mixtures
and substrate material. Reference to literature databases
on coloured manuscripts and previous work carried out in
our laboratories on wall-paintings and frescoes enabled us
to assign the majority of the spectroscopic features unambiguously. The Raman spectrum of the standard (commercially available) tin(IV) sulfide sample is shown in
Fig. 1; the spectrum is very simple and consists of a very
strong band at 313 cm 1 , assignable to (SnS) symmetric
stretching, and weaker bands at 571 and 203 cm 1 .
Figure 2 shows a stack-plot of some sulfide pigments
which were used in antiquity, namely orpiment, realgar,
Figure 1. FT-Raman spectrum of tin(IV) sulfide powder (Aldrich
Chemical Co); 1064 nm excitation, 200 scans at 4 cm 1 spectral
resolution; wavenumber range 50 1000 cm 1 .
EXPERIMENTAL
Samples
The standard sample of tin(IV) sulfide was obtained from
the Aldrich Chemical Co. as a 99% pure, golden yellow,
crystalline material. It was used without further purification.
Raman spectroscopy
Raman spectra were obtained using a Bruker IFS66
infrared instrument with FRA106 Raman module attachment and 1064 nm near-infra-red radiation from a Nd3C /
YAG laser. The tin(IV) sulfide standard sample proved
to be a very strong scatterer and spectra of good signalto-noise could be obtained at 4 cm 1 spectral resolution
with 200 accumulations. The yellow and brownish-yellow
Copyright  2000 John Wiley & Sons, Ltd.
Figure 2. Stack-plotted Raman spectrum of sulfide pigments
used in antiquity: a orpiment; b realgar; c mosaic gold;
d cinnabar. Conditions as for Fig. 1 but wavenumber range
50 650 cm 1 .
J. Raman Spectrosc. 31, 407–413 (2000)
RAMAN SPECTROSCOPIC STUDIES OF A 13th CENTURY STATUE
409
Table 1. Raman band wavenumbers (ñ) for sulfide
pigments used in antiquity
Pigment
Cinnabar
Mosaic Gold
Orpiment
Realgar
(Q)/cm
253
285
347
203
313
144
160
205
298
309
360
387
125
147
156
170
194
230
239
308
342
353
1
Protocol for identificationa
vs
w
m
vw
vs
w
w
vw
m
ms
vs
w
w
w
w
w
m
w
ms
w
ms
ms
p
p
p
p
p
p
p
a
This protocol represents the band(s) in the Raman
spectra of the pigment which are considered most
suitable for characterization.
cinnabar and mosaic gold, from which it is seen that the
strong 313 cm 1 band in tin(IV) sulfide is characteristic of
this material. The main vibrational Raman spectroscopic
bands are given in Table 1, from which it is seen that the
following protocol could be suggested for the discrimination between ancient sulfide pigments. The Raman spectra
of orpiment and realgar (Fig. 2a and b) are clearly much
richer in vibrational bands than those of cinnabar and
mosaic gold. Nevertheless, the suggested protocol from
Table 1 would be that cinnabar is clearly characterized
by a feature at 253 cm 1 ; the strong band at 313 cm 1
in mosaic gold differentiates this material from cinnabar,
but there is a band nearby in orpiment at 309 cm 1 . However, orpiment has another band at 360 cm 1 of similar
intensity which is not present in the spectrum of tin(IV)
sulfide. Realgar can also be distinguished from the other
pigments, but this involves a three-band identification pattern at 239, 342 and 353 cm 1 , all of similar peak heights
to each other under the experimental spectroscopic conditions of the present work. The spectroscopic protocol
(Table 1), therefore, involves single identification bands
for cinnabar and mosaic gold but the use of a doublet for
orpiment and a triplet for realgar.
However, admixture or adulteration of pigments was
quite a common practice in antiquity and this can pose
further problems for analytical spectroscopy, while the
information obtained from these analyses can sometimes
provide unique molecular information about ancient technologies and painting techniques.
Red pigments
These occurred on two areas of the figure; the cape was
a bright orange-red (1 in Plate 1) and the belt was a dark
red (10 in Plate 2), and thus appear to be painted with two
Copyright  2000 John Wiley & Sons, Ltd.
Figure 3. FT-Raman spectra of the red pigment (specimen 1 in
Plate 1) from the statue compared with standard red pigments
in use at mediaeval times and the substrate; 1064 nm excitation,
wavenumber range 50 1200 cm 1 . Spectra from top: a cinnabar
from Almaden mines; b cinnabar from Tarna mines; c red
pigment, specimen 1, from statue; d lead(II) lead(IV) oxide;
e specimen of substrate from statue.
different pigments. The Raman spectrum (Fig. 3) of the
cape sample showed evidence for a mixture of cinnabar,
mercury(II) sulfide (HgS), with bands at 252, 283 and
342 cm 1 and lead(II) lead(IV) oxide, red lead (Pb3 O4 ),
with bands at 544 and 387 cm 1 . As the cape is of uniform
colour throughout, it may be inferred that the pigment
mixture was chosen for its special colour initially; later
restoration might have resulted in a rather ‘patchy’ appearance. Weaker bands in the spectrum (not shown) occur at
1007 and 1086 cm 1 , characteristic of gypsum and calcite, respectively—the former probably applied as a wet
layer to the stone statue substrate before application of the
pigment colour. Cinnabar was always expensive, and its
adulteration with haematite (Fe2 O3 ) or lead(II) lead(IV)
oxide was common in Roman and mediaeval times, particularly as an economic necessity. However, we do not
believe that the adulteration here is attributed to economy
because of the religious significance and importance of the
statue. Also, the cinnabar used does not contain the Raman
band of ˛-quartz at 463 cm 1 which is always associated
with an Almaden mines volcanic source; instead, the presence of the small amount of calcite could indicate a local
mineralogical source such as the Tarna mines in Castille
y Léon, Spain. A previous Raman spectroscopic study13
of Roman frescoes from King Herod’s summer palace
in Jericho (ca. 10 BC) has provided a base for our identification of Almaden and Tarna-sourced cinnabar. From
quantitative measurements of the relative intensities of the
544 and 252 cm 1 bands in red lead and mercury(II) sulfide, respectively, and comparison with calibration graphs
constructed from red lead-cinnabar mixtures of known
composition12 we calculate that the composition of the
red pigment used in the cape of the statue is about 90%
red lead and 10% cinnabar.
There is a possibility that the red pigmentation of
the cape and belt were achieved by a two-stage process
of application of cinnabar over red lead, which is a
documented practice in mediaeval polychromy. However,
the ‘masking’ effect of the very much stronger cinnabar
bands over those of the weaker red lead (molar scattering
coefficient ratio of the bands at 252 and 547 cm 1 of
HgS and Pb3 O4 , respectively, is about 65), would tend to
J. Raman Spectrosc. 31, 407–413 (2000)
410
H. G. M. EDWARDS ET AL.
Yellow-brown pigments
Figure 4. FT-Raman spectra of dark red pigment from statue.
Conditions as for Fig. 3. From top: a specimen 10 in Plate 1;
b red lead; c cinnabar from Tarna mines.
negate this possibility as our Raman spectra from several
particles of red pigment are identical.
The Raman spectrum of the dark red pigment (Fig. 4)
on the belt of the statue (sample 10 in Plate 2) shows
several unusual features. Firstly, there is no evidence in
the spectrum for the usual red mineral pigments such
as cinnabar, red ochre, Mars red or red lead. Two weak
features at 1086 and 1051 cm 1 are assignable to .CO3 2 /
modes in calcite and lead white, respectively. Broad bands
at 1599 and ¾1300 cm 1 indicate carbonaceous material
and in the absence of (CH) modes near 3000 cm 1 , we
conclude that this is probably amorphous carbon and not a
coloured resin. The identification of this deep red pigment
is, therefore, not possible on the basis of the spectra
obtained here, but the broad band at 239 cm 1 could be
indicative of a metal oxide.
Black pigments
Specimens 7 and 4 in Plates 2 and 3, from tunic cuff
and sandal, respectively, are clearly lamp-black soot-based
pigments with characteristic Raman bands due to amorphous carbon at 1590 and 1330 cm 1 (Fig. 5). Absence
of a feature at 960 cm 1 due to phosphate indicates that
the carbon is not based on calcined bone or ivory.
Figure 5. FT-Raman spectra of black pigment from statue
(specimens 4 (Plate 3) and 7 (Plate 2)). Conditions as in Fig. 3.
Wavenumber range 200 1700 cm 1 .
Copyright  2000 John Wiley & Sons, Ltd.
Specimens 5 and, 6 (Plate 3) and 11 (Plate 1) represent samples from the dress hem, cape hem and coif,
respectively. The Raman spectrum of specimen 5 shows
a medium intensity band at 281 cm 1 , with weaker features at 156 and 388 cm 1 . This does not match that of
any known yellow mineral sulfide pigment, but bands at
1086, and 712 cm 1 indicate the presence of calcite or
chalk white and bands at 1317, 1437, 1582 cm 1 indicate
that an organic source is likely.
Specimen 6 (Plate 3) has a very different Raman spectrum (Fig. 6) in that it has prominent features at 145,
253, 284, 390, 550 cm 1 as well as the chalk mode at
1086 cm 1 and one ascribed to limewash or silicates near
784 cm 1 . A mixture of red lead and cinnabar with chalk
and an unidentified organic pigment is indicated here.
Specimen 11 (Plate 1) is more brown than the other
two studied here and with bands at 253, 286, 343 and
396, 415 cm 1 is considered to be a mixture of yellow
ochre and cinnabar.
The Raman spectrum of the golden-coloured specimen
(SA6) from the 13th century Santa Ana statue is clearly a
mixture since several bands due to lead(II) lead(IV) oxide,
red lead or minium, are present along with other features.
However, the orange-red colour of the minium is changed
to a deep golden colour by admixture with another pigment; a band at 313 cm 1 is now attributable to tin(IV) sulfide and other bands at 253 and 343 cm 1 can be ascribed
to cinnabar. In Fig. 6 the stack-plot of SA6, cinnabar, red
lead and tin(IV) sulfide is shown; the characteristic features of red lead and cinnabar are clearly broadened in the
SA6 sample, but the presence of a new, broad feature of
medium-strong intensity at 290 cm 1 is also present. The
broad, medium intensity band at 150 cm 1 along with the
290 cm 1 feature indicates the presence of massicot or
litharge, PbO. The Raman spectrum of a 1 : 1 molar mixture and tin(IV) sulfide (Fig. 7) shows that the presence of
mosaic gold in admixture with red lead can be detected.
Our calculations reveal that the molar scattering factors
for SnS2 : Pb3 O4 are in the ratio of 125 : 1, based on the
characteristic features of each specimen at 313 cm 1 and
547 cm 1 , respectively, although the band of red lead at
125 cm 1 is considerably stronger than that at 547 cm 1 ,
it is also in a region which is susceptible to considerable
Figure 6. Stack-plotted Raman spectra of a golden-yellow sample from the 13th century statue of Santa Ana (SA6) with
b cinnabar; c red lead (minium); d tin(IV) sulfide for comparison.
Conditions as for Fig. 2.
J. Raman Spectrosc. 31, 407–413 (2000)
RAMAN SPECTROSCOPIC STUDIES OF A 13th CENTURY STATUE
interference from spectral features of other components in
mixtures.
Hence, we conclude that the composition of the golden
yellow pigment SA6 on the Santa Ana statue is a complex
one consisting of minium, cinnabar, mosaic gold and
litharge/massicot. The identification of genuine massicot
(PbO) and the historical confusion in terminology with
other lead oxide pigments, especially lead tin yellow and
lead antimonate yellow has been elegantly considered
in a previous paper by Clark et al.22 The reason for
the presence of such an apparently complex mixture of
pigments on the 13th century polychrome statue will be
considered later.
In contrast to the pigment composition of the specimen SA6, the Raman spectrum of the brownish-yellow
specimen SA5 cannot be similarly ascribed (Fig. 8). It
appears that this specimen is a simple mixture of massicot/litharge, lead(II) oxide, and red lead; clearly there is
no mosaic gold present here as the band at 313 cm 1 is
absent. Visually, the two pigmented regions of the statue
are significantly different.
The very different material compositions of these two
yellow pigments which are in close proximity to each
other on the polychrome statue (Plate 3) raises the interesting question as to the possible significance of the mixtures: SA5: massicot/litharge and red lead; SA6: minium,
cinnabar, massicot/litharge and mosaic gold.
411
The red cape of the statue has been identified as a
minium-cinnabar mixture; from quantitative studies of the
Raman spectra of standard minium-cinnabar mixtures, we
have calculated that the composition of the cape and of
the minium-cinnabar content of the hem are identical, and
this represents a 90 : 10 mixture of red lead and cinnabar.
In an experiment designed to evaluate the relative
molecular scattering factors of SnS2 and Pb3 O4 , an equimolar mixture of tin(IV) sulfide and red lead represented
by masses of 30 mg and 70 mg, respectively, was finely
ground in an agate pestle and mortar and subjected to
Raman spectroscopic analysis. The result is shown in
Fig. 7; here, although the strong band ascribed to .SnS2 /
stretching is clearly seen at 313 cm 1 , there is only little
evidence for red lead in the spectrum at all. As indicated above, the relative molar-scattering factor for tin(IV)
sulfide and red lead bands at 313 and 547 cm 1 , respectively, is about 125. Inspection of the grinding surface of
the pestle following the mixed pigment preparation was
undertaken; this was found to be coated with a golden mirror deposit. In a further experiment, a small quantity of
the equimolar mixture of red lead and tin(IV) sulfide was
ground between two polished glass plates. The golden mirror formed was washed and its Raman spectrum recorded;
only a weak, broad feature centred on 500 cm 1 could be
seen, no Raman bands could be identified and ascribed to
red lead or to tin(IV) sulfide and we attribute the formation
of the mirror to a lead-tin alloy.
The golden mirror formed by the burnishing of the
red lead/tin sulfide mixed pigment for several minutes at
room temperature was subjected to an EDAXS analysis
using LINK ISIS and a germanium detector. The crystalline material (Fig. 9) gave an energy spectrum which
demonstrated the presence of lead and tin with sulfur and
a trace of copper (Fig. 10). The origin of the copper signal
can only be speculated on. This result is consistent with
our supposition of the formation of a lead–tin alloy by the
burnishing of the pigment mixture. The absence of Raman
bands due to lead oxide and tin sulfide from this specimen
is also explicable as, clearly, the red lead and tin sulphide
have chemically reacted to produce a lead–tin alloy. The
presence of sulfur in the EDAXS spectrum analysis could
suggest the origin of the weak Raman band at ¾500 cm 1
Figure 7. FT-Raman spectrum of equimolar (1 : 1) mixture of
SnS2 and Pb3 O4 . a red lead; b 1 : 1 red lead and tin(IV) sulfide;
c tin(IV) sulfide. Conditions and range as for Fig. 3.
Figure 8. FT-Raman spectrum of: a brownish-yellow pigment
(SA5) on Santa Ana statue; b red lead; c tin(IV) sulfide;
d massicot/litharge, PbO.
Copyright  2000 John Wiley & Sons, Ltd.
Figure 9. Scanning electron microphotograph of the golden
mirror formed by the burnishing of a red lead/tin sulfide pigment
mixture for several minutes at room temperature. Magnification
950ð, eht 8.3 kV, scale bar 10 µm.
J. Raman Spectrosc. 31, 407–413 (2000)
412
H. G. M. EDWARDS ET AL.
Figure 10. EDAXS energy spectrum of the golden mirror sample
in Fig. 9 showing the presence of lead, tin, sulfur (and trace of
copper).
in the spectrum of the mirror specimen, since elemental sulphur (S8 ) has a strong band at 494 cm 1 . On the
basis of these analyses, we therefore suggest that a reaction has taken place between the lead(II) lead(IV) oxide
(2PbOÐPbO2 ) and the tin sulfide (SnS2 ) to give a lead-tin
alloy and elemental sulfur.
An interesting conclusion can be drawn from these
results, for it appears that the addition of tin(IV) sulfide
to lead(II) lead(IV) oxide yields a mixture which can be
easily burnished to give an attractive deep golden mirrorlike finish, suitable perhaps for delicate statuary and works
of art. We repeated the grinding experiments with tin(IV)
sulfide alone and found that it was difficult to produce a
good mirror finish; also, heavier, prolonged burnishing of
tin(IV) sulfide and lead tetroxide using rougher materials
did not give a mirror finish but resulted in black, powdery
deposits, probably of PbS and SnO.
With regard to the specific treatment found here on
the Santa Ana statue, it is apparent that the application
of a layer of tin(IV) sulfide to the cape pigment (a 9 : 1
mixture of red lead and cinnabar) has resulted in a deepgolden metallic colour. The Raman spectrum of the SA6
sample hence shows the band of tin(IV) sulfide weakly
at 313 cm 1 , with the red lead and cinnabar features also
being apparent.
Organic components are also present in several of the
yellow-brown specimens since there are (CH) modes at
2852, 2887 and 2933 cm 1 , as well as υ.CH2 / modes near
1440, 1406, 1362 and 1298 cm 1 . These in conjunction
with the sharp peak at 1050 cm 1 are possibly due to a
resin binder.
Flesh pink pigment
In Fig. 11, the major bands in sample 8 in Plate 2
(statue hand) arise from an organic and inorganic pigment
mixture; cinnabar is evident from the band at 253, 283 and
343 cm 1 , whereas a broader weaker feature at 415 cm 1
indicated iron(III) oxide bands at 1050 and 1086 indicate
lead white and calcite (chalk), used as whitening agents,
but weaker υ.CH2 / modes near 1300, 1350 and 1438 cm 1
along with (CH) modes at 2856, 2888 and 2936 cm 1
(Fig. 12) indicate the presence of an aliphatic organic
compound.
Copyright  2000 John Wiley & Sons, Ltd.
Figure 11. FT-Raman spectra of flesh-pink pigment (specimen
SA8) from Santa Ana statue: a specimen SA8; b red lead;
c cinnabar from Tarna mines. Conditions as in Fig. 3, wavenumber range 50 1200 cm 1 .
Figure 12. As for Fig. 11, but wavenumber range 2700
3100 cm 1 ; only the SA8 specimen has a Raman signal in this
wavenumber region, the red lead and cinnabar do not.
Grey pigment
A specimen from the head-dress of the statue, sample 9
in Plate 1 again shows evidence of calcite and lead
white with no evidence of carbon. Bands at 2914, 2880
and 2853 cm 1 in the (CH) stretching region and a
broad feature centred at 1307 cm 1 may be ascribed to
an organic binder. The grey colour is attributed to a
deterioration of the lead white to black lead sulfide; this
effect has been reported hitherto for manuscripts.1
The green samples, specimens 2 and 3 (Plates 2 and
3), did not give good Raman spectra with near-infrared excitation at 1064 nm—no pigment bands could be
identified, only medium-strong intensity features due to
calcite and gypsum.
While in the course of preparation of this paper, we
became aware of the publication of a Raman spectroscopic
study of mediaeval illuminated Latin manuscripts23 in
which the authors had attempted to identify mosaic gold in
their samples. Their conclusion was that metallic gold had
been used in their specimen; however, they commented
on two types of crystalline tin(IV) sulfide which had been
synthesized by co-workers in their project, one of which
was likened to a shiny silver-like material. The Raman
spectra of both contained a strong band at 305 cm 1 ,
but the golden crystals also had a weaker feature at
J. Raman Spectrosc. 31, 407–413 (2000)
11
1
2
10
7
9
8
Plate 1. Photograph of the XIIIth century Santa Ana Statue, indicating
the locations from which pigment specimens were taken for Raman
spectroscopic analysis
Plate 2. Photograph of the XIIIth century Santa Ana Statue,
indicating the locations from which pigment specimens were taken for
Raman spectroscopic analysis
6
3
5
4
Plates 3. Photograph of the XIIIth century Santa Ana Statue, indicating the locations from which
pigment specimens were taken for Raman spectroscopic analysis
Copyright © 2000 John Wiley & Sons, Ltd.
J. Raman Spectrosc. 31 (2000)
RAMAN SPECTROSCOPIC STUDIES OF A 13th CENTURY STATUE
226 cm 1 . We would confirm the assignment of both
synthetic species as mosaic gold, but also suggest on the
basis of our experiments that the ‘shiny silver’ form of
SnS2 reported by these authors could be a mirror-like
crystalline deposit. We actually could obtain a mirror-like
film from SnS2 alone, but the depth of colour and ease
of formation when in admixture with Pb3 O4 is worthy of
note here.
413
indicated the presence of organic compounds; the aliphatic
(CH) stretching modes and bands in the 1300–1500 cm 1
region are suggestive of the presence of gums or resins
which perhaps were used either as binders to assist the
adhesion of pigments to the substrata or varnish which
has been applied post-decoratively for the protection and
enhancement of the statue’s appearance.
Acknowledgements
CONCLUSIONS
The Raman spectroscopic analysis of paint specimens
from a 13th century polychrome statue has produced
some novel information. In almost all cases, the spectra
We are grateful to the Junta de Castille y Leon for permission to take
pigment samples from the 13th century statue, to the British Council
(Madrid) and the Spanish Ministry of Science for an Accion Integrada,
during the tenure of which this work was carried out, and to Ken
Robinson of the British Antarctic Survey at Cambridge for the EDAXS
results.
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