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Analysis of pigments from Roman wall paintings found in
Vicenza
G.A. Mazzocchin a,*, F. Agnoli a, S. Mazzocchinb, I. Colpo b
a Dipartimento di Chimica Fisica, Universita CaFoscari di Venezia, Calle Larga S. Marta 2137, Venezia 30123, Italyb Dipartimento di Scienze dellAntichita, Universita di Padova, Piazza Capitaniato 7, Padova 35139, Italy
Received 18 February 2003; received in revised form 6 May 2003; accepted 23 May 2003
Abstract
The analysis of about 60 samples of wall paintings was carried out using different chemicophysical techniques: optical
microscopy, scanning electron microscopy (SEM) equipped with an EDS microanalysis detector, X-ray powder
diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The identified pigments were cinnabar,
hematite, red ochre, celadonite, cuprorivaite (Egyptian blue), yellow ochre, goethite and carbon. Only in one case some
lead white was found instead. In general, the mortar preparation did not correspond to the complex structure suggested
by Vitruvius (De Architectura), but it generally showed a porous layer, with crushed grains under the pigment layer. Incertain cases two superposed pigment layers were found: yellow superimposed on both red and pink, black on pink,
green on black.
# 2003 Elsevier B.V. All rights reserved.
Keywords: Roman pigments; Wall paintings; Physicochemical analysis; EDS; XRD; FTIR
1. Introduction
Paintings and colour remains of the Roman Age
have been discovered and picked up for over a
century. Among the most important discoveries,Pompeii and Rome stand out [1].
In France and Switzerland, a systematic analysis
on the found fragments was performed [2/5]; in
Spain, scientific research on archaeological finds is
sprouting[6,7].
In Italy, there is a lack of a systematic analysis
of the numerous Roman painting finds, but the
research is now increasing.One of the most important questions in the
analysis of ancient paintings is the nature of the
pigments used. The analysis, in fact, gives infor-
mation useful in defining the gamut of pigments
available at a local, regional or even wider scale
and to understand the techniques of colour pre-
paration and application. In addition, through the
study of pigments, it is possible to discover the
lines of communication and trade exchange.
* Corresponding author. Tel.: /39-041-234-8530; fax: /39-
041-234-8594.
E-mail address: [email protected] (G.A.
Mazzocchin).
Talanta 61 (2003) 565/572
www.elsevier.com/locate/talanta
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The aim of the present work is the study of
about 60 fragments of few square centimetres of
wall painting coming from an archaeological
excavation in a Roman Villa in Vicenza (ContraPedemuro, S. Biagio) directed by the Sovrinten-
denza Archeologica per il Veneto by Dr. Luigi
Malnati and Prof. Gian Pietro Brogiolo of the
University of Padova.
The techniques used were optical microscopy,
scanning electron microscopy (SEM) equipped
with an EDS microanalysis detector, X-ray pow-
der diffraction (XRD) and Fourier transform
infrared spectroscopy (FTIR).
The coupling of the used techniques, most of
which non-destructive, suitable for the determina-tion of anionic groups, crystalline phases, structure
and elemental composition allowed us to have a
complete enough characterisation of the used
pigments, materials and techniques.
2. Experimental
2.1. Sampling
The sampling was made by the archaeologicalteam, which collected pieces representative of the
variety and differences of colour. The dimension
of the fragments analysed ranged from 2 to 20/25
cm2, but it is quite hard to have a precise idea of
the dimensions of the whole frescoes because all
the painted walls were found as fragments covered
by mould and rubble.
2.2. Optical microscopy
The samples were observed by means of an
optical microscope Wild-Leitz M8 with a 19.2/
to 256/ zoom. The samples were illuminated
using a movable fibre glass system. This technique
was used specially in the examination of the grains,
crushed calcite or other tiny stones inside mortars.
2.3. Scanning electron microscopy
SEM images were taken using a Jeol (Tokyo,
Japan) JSM 5600 LV equipped with an Oxford
Instruments 6587 EDS microanalysis detector.
The images were taken under low vacuum condi-
tions where samples did not show any charging
effects; in this way, it was possible to avoid the
coating of the samples with a high-conductancethin film (gold or graphite films).
EDS microanalysis was made to obtain infor-
mation on the elemental composition of the
sample.
2.4. X-ray powder diffraction
XRD was used to identify the different crystal-
line phases present in pigments. A Philips XPert
vertical goniometer with Bragg-Brentano geome-
try, connected to a highly stabilised generator, wasused for XRD analysis. Cu Ka Ni-filtered radia-
tion, a graphite monochromator on the diffracted
beam and a proportional counter with pulse height
discriminator were used. Measurements in a 5/608
range were taken with a step size of 0.058 and 2
seconds per point.
2.5. Infrared spectroscopy (FTIR)
Absorption spectra in the IR region were
collected using a Nicolet Magna 75 FTIR spectro-meter. Thirty-two signal-averaged scans were ac-
quired on the samples. Few milligrams of each
sample were diluted in KBr (IR grade, Merck)
pellet with a diameter of about 13 mm.
3. Results and discussion
3.1. Pigments identification
The analysed samples, the stratigraphic unitthey belong to, the identified pigments and the
analytical techniques used are shown in Table 1.
3.2. Black
In Fig. 1, we show a 200/ SEM image
performed on a black sample (S.U. 784). From
this image one can see the homogeneous distribu-
tion of a fine-grained black. A trace, left on the
mortar during its preparation, is also visible.
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XRD analysis does not show the presence of
crystalline phases related to the presence of black
colour, and this suggests the use of amorphouscarbon for the preparation of this pigment. FTIR
analysis showed that the pigment is mainly made
of CaCO3, as demonstrated by the bands centred
at 1435, 875 and 715 cm1 assignable to CO3
group and the band centred at 3450 cm1 related
to the water OH group stretching, while the band
around 1100 cm1 is due to small amounts of
silicates.
The black colour disappears when the sample is
heated at 500 8C in muffle oven, confirming the
use of carbon (coal black, soot) as dyestuff. EDS
analysis (Fig. 2) showed the presence of C and
revealed the absence of P (due for example to bone
black) and of dark metal oxides, which suggest the
use of coal black as a basis for the preparation of
this pigment. The presence of Al, Si and Ca is
related to the mortar below.A sample, belonging to the stratigraphic unit
256, showed the presence of a pink colour laying
on a coal black layer. Both colour layers were
spread before the complete exsiccation of the
support because, looking at the FTIR spectrum,
Table 1
The analysed samples, the stratigraphic unit they belong to, the identified pigments and the analytical techniques used
Colour Number of sam-ples Stratigraphicunit Identified pigments Technique
Black 4 784 Coal black FTIR, SEM, EDS, XRD, muffle
oven test
Pink on black 1 256 Coal black FTIR, SEM, EDS, XRD, muffle
oven test
Grey 8 456, 784 Coal black and bone black FTIR, SEM, EDS, XRD, muffle
oven test
Blue 3 784 Cuprorivaite FTIR, EDS, XRD
Clear blue 2 784 Cuprorivaite FTIR, EDS
Red 10 313, 766, 784 Hematite FTIR, EDS, XRD
Violet 3 226, 784 Hematite FTIR, SEM, EDS, XRD
Cinnabar red 2 784, 766 Mercuric sulphide FTIR, SEM, EDS, XRD
Green 5 766, 784 Cuprorivaite, celadonite, glauconite FTIR, SEM, EDS, XRDIvory 2 766 Calcite, yellow ochre FTIR, SEM, EDS, XRD
Yellow 5 766 Limonite, yellow ochre, goethite FTIR, SEM, EDS, XRD
Stripes, bands and
figures
10 456, 784 Lead whites and other pigments
above cited
SEM, EDS
Fig. 1. SEM image of the black sample.
Fig. 2. EDS spectrum of the black sample.
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around 2900 cm1 we did not find detectable
quantity of organic matter as binder or dyeing
stuff; the matching of different colour layers is
reported in literature[2].The EDS analysis of thepink colour revealed the presence of large quan-
tities of Al, Si and small quantities of Fe and K,
suggesting the presence of clay minerals together
with CaCO3.
3.3. Grey
Many grey samples, belonging to the S.U. 456,
were found in the excavation site.
EDS analysis (Fig. 3) revealed a small amount
of C, big quantity of Ca and O, significantamounts of P, Al and Si, and traces of Fe, Mg,
K and S. Like the black sample, when the grey
sample was heated in a muffle oven at 500 8C, the
colour tends to disappear and this behaviour is
indicative of the presence of carbon.
Looking at the low-magnification SEM images,
one can see that the colour seems to be spread
smoothly throughout and adherent to the layer
below, while calcite reflecting crystals crop out.
XRD analysis (Fig. 4) revealed the presence of
calcite, with traces of quartz and phosphoruscompounds.
FTIR analysis shows the main presence of
calcite, with traces of Fe oxides (560 and 470
cm1) and silicates (900/1100 cm1).
Hence, we can state that our grey sample is not
constituted of ash containing metal oxides, as
suggested by Bearat [3], but mainly of coal black
with traces of bone black and of superficial calcite
crystals added to confer brilliance to the painting.
3.4. Blue and clear blue
All the examined blue samples were constitutedby Egyptian blue (differently diluted by CaCO3), a
compound produced since the time of ancient
Egypt time by means of a high-temperature (/
800 8C) synthesis starting from siliceous sand, a
copper compound, calcium carbonate and sodium
carbonate as a flux. In the correct proportion,
these chemicals together create a product of
formula CaCuSi4O10, which corresponds to the
cuprorivaite mineral[8,9].
EDS analysis of a deep blue sample is shown in
Fig. 5. XRD analysis confirmed that the blue
sample was constituted by cuprorivaite with tracesof silica and residual calcite. The presence of
calcite, as confirmed by FTIR analysis, could
also be indicative of an incomplete synthesis. The
spectrum also reveals the presence of the Si/O
stretching bands at 1011 and 1051 cm1 [10].
This pigment, which Vitruvius and Pliny defined
caeruleus, was found in the wall paintings of
many Roman sites [1,11,12]. It is used alone or
added to other colours to confer more brilliance or
different hues. In the case of the villa in Vicenza,Fig. 3. EDS spectrum of the grey sample.
Fig. 4. XRD spectrum of the grey sample with the crystallinephases calcite, phosphorous oxides and quartz, and a diffuse
halo typical of amorphous substances.
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the blue pigment was added just to the green made
of celadonite and glauconite.
3.5. Red and violet
Red samples were rather numerous; different
red hues were analysed: an orange red; a brick red;
a brilliant red; a violet red and a wine violet.
The XRD analysis of a wine violet, the EDS
spectrum of the violet red (Fig. 6) and the FTIR
allowed us to verify that the colour is due to the
presence of hematite in different quantities, ac-
cording to the areas of FTIR and EDS peaks and
to the hue of the sample: in the lighter samples
(orange red) a smaller quantity of hematite was
present with respect to the darker ones like the
wine violet which is made of pure hematite [6]. By
diluting hematite with CaCO3 a pink colour is
obtained, while brilliant red hues could be ob-
tained by using different ochres.
3.6. Brilliant red*/cinnabar
A particular attention was paid to the brilliant
red sample. In fact, it is not made of hematite, but
of cinnabar (mercuric sulphide). Though cinnabar
is considered a precious pigment, we did not find
substantial differences in the preparation of themortar below, which was made by a Ca(OH)2layer of about 1/2 mm immediately below the
pigment, followed by Ca(OH)2 with crushed
calcite crystals and then by a mortar with sand
and/or tiny river stones. In one of the examined
sample, a thin yellow pictorial film was found
below the brilliant red. It is worth noting that all
the samples are very well preserved [13]. EDS
spectrum is shown in Fig. 7, while the XRD
spectrum is shown inFig. 8. In both spectra, one
can see the sole presence of cinnabar. The extrac-tion of the possible protective films carried out
using methylene chloride or xylene did not show
any characteristic of oils or preservative pitch by
FTIR analysis.
Fig. 5. EDS spectrum of the blue sample.
Fig. 6. EDS spectrum of the violet red sample. Fig. 7. EDS spectrum of the cinnabar sample.
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3.7. Green
There were a number of green samples of
different hues, from grey green to blue green to
mossy green to grass green.
Some samples are characterised by a double
pictorial layer: a dark grey under a light green
layer.
XRD spectra of a grass green sample pointedout the presence of celadonite and cuprorivaite
besides traces of glauconite. The presence of
celadonite confers to the sample the green colour.
3.8. Ivory
An ivory white sample was made of calcite with
traces of dolomite and iron oxides, as can be
clearly seen from EDS (small peak of Fe) and
FTIR (560 and 490 cm1) spectra. This hue of
colour can be reached also by pinkish and greenpigments which underwent changes as time passed.
3.9. Yellow
The yellow ochre painting pigments analysed
are characterised by a double pictorial layer. We
found a yellow on red and a yellow on a pink
basis. We also got a yellow with plain traces of
coal black on the surface. In Fig. 9, the XRD
spectrum of a yellow sample shows goethite as
main crystalline phase, besides other iron hydro-
xides.
EDS and FTIR analyses confirmed that the
pictorial layer is mainly made of iron oxides and
hydroxides[6]. The absence of As and Pb allowed
us to exclude the use of orange compounds like
Pb3O4 or As2S3 to obtain the yellow colour. Thepresence of Al, Fe, Si and K, revealed by means of
EDS analysis, suggests the use of clay minerals,
which allowed us to define the yellow pigment as
an ochre.
The yellow ochre sample with traces of coal
black put in muffle oven at 500 8C showed the
disappearance of the surface blackish patina and
the persistence of the yellow, which got a darker
hue. Consequently, the coal black can be ascribed
to the residual combustion products due to the
lighting of the env
ironment, or as a consequence ofa fire.
3.10. Non-homogeneous pieces (lines, stripes,
figures)
Together with monochromatic wall painting
pieces, many fragments with white, pink, dark
red, and blue lines and stripes on a grey layer were
found. Some of these pieces are shown in Fig. 10.
Fig. 8. XRD spectrum of the cinnabar sample with the
crystalline phases cinnabar and calcite. Fig. 9. XRD spectrum of the yellow sample with the following
crystalline phases: goethite, quartz, calcite and other iron
hydroxides.
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FTIR analysis of the grey layer showed the
typical bands of the carbonate and of the silicon/
oxygen group. Generally, the grey of the striped
samples had the same characteristics of the mono-
chromatic grey sample. XRD analysis confirmed
that the pigment is mainly made of calcite. The
crystals on the surface confer brightness to the
colour.
The v
iolet and blue stripes of the pieces inFig.10did not show any novelty, since they were made,
respectively, of hematite and cuprorivaite, while
the white line of these pieces revealed the presence
of Pb, due to the use of cerussite (PbCO3), or white
lead (2PbCO3 /Pb(OH)2).
Among the non-homogeneous pieces there was
a blackish grey angular piece (decorated with
white, pink and blue stripes) which, most prob-
ably, was the rounded edge of a wall. The material
below the painting was very hard, perhaps because
accurately worked. SEM, EDS and FTIR analyses
showed that the pigment used was the same blackcoal of the grey monochromatic sample previously
described. Also in this case, the pink line was made
of hematite diluted by calcite, the white was made
of pure calcite and the blue was cuprorivaite.
In this group of samples we also examined a wall
fragment painted with colours from lilac to pink,
with blue strokes of brush and weak yellow stripes
(Fig. 11). The main components of the used
pigments are analogous to the red and blue already
described for the monochromatic samples, except
for the thick pink colour, which is not made of
diluted hematite, but of diluted cinnabar, confirm-
ing the preciousness of the painting.
4. Conclusions
Ev
en if modest with respect to the v
ariety ofcolours found in other archaeological sites like in
Rome or Pompeii [1,11,12], the Vicenza palette is
rich and includes, besides the ordinary pigments,
precious pigments like cinnabar and Egyptian blue
and well-done paintings.
The adding of refracting materials such as
Egyptian blue was used exclusively for the green
pigment, while calcite was used for the grey one;
we also found the use of different combinations of
pictorial layers.
We did not find a wide use of lead as orange
(minium, Pb3O4) or as white (cerussite, PbCO3;white lead, 2PbCO3 /Pb(OH)2), while we found
practically the whole gamut given by hematite
(orange red, red, brick red, violet) and by cinnabar
(brilliant red and pink). We never identified
organic ligands or pigments which could lead one
to think about pictorial techniques different from
frescoes.
We did not find As-based pigments which, on
the contrary, were found in Gallia, in Argentoma-
gus[14].
Fig. 10. Picture of some pieces with white, pink, dark red andblue lines on a grey layer.
Fig. 11. Picture of a wall fragment painted with colours fromlilac to pink and with blue strokes and yellow stripes.
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Different kind of mortars were used for the
walls of this villa, but, in general, the preparation
of these supporting materials was not exactly the
one already suggested[15,16].
However, we think that the white and porous
layer of Ca(OH)2 with crushed calcite crystals of
about 2 mm of length (Fig. 12) was made on
purpose in order to make the layer resistant and at
the same time resilient and porous. Finally, we can
state that the employed analytical techniques are
suitable to give the information required for thecharacterisation of the pigments found.
Acknowledgements
The authors are grateful to Dr. Carlo Bragato
and Mr. Danilo Rudello for helpful assistance.
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Fig. 12. SEM image of crushed calcite grains under the
cinnabar pigment layer.
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