Vibrational spectroscopy at the service of industrial archaeology: Nineteenth-century wallpaper
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ARTICLE IN PRESS
Trends in Analytical Chemistry, Vol. XX, No. X, 2007 Trends
Vibrational spectroscopy at the
service of industrial archaeology:
Nineteenth-century wallpaper
K. Castro, A. Sarmiento, E. Princi, M. Pérez-Alonso, M.D. Rodrı́guez-Laso,
S. Vicini, J.M. Madariaga, E. Pedemonte
We present an overview of the application of some vibrational spectroscopic 1. Introduction
techniques (Fourier transform infrared (FTIR) and Raman) to industrial arc-
haeology in the field of cultural heritage, particularly centered on the Scientific study of artworks used to be in
wallpaper industry. Both techniques present a better performance for cost vogue because of its novelty and, in many
than other set-ups applied to the analysis of multilayer artworks on cellulose cases, to test the analytical instrumental
supports. To illustrate the applicability of these techniques, we present techniques on matrices different from the
examples of different decorative wallpapers from the whole nineteenth classical ones (e.g., wastewaters and pol-
century and compare the results obtained with other artworks from the same luted soils). Nowadays, by contrast, these
century. kinds of scientific study are common
Raman spectroscopy was mainly used in pigment determination with the practice in many museums and institu-
help of FTIR spectroscopy. The study of the binder was better achieved using tions dedicated to study and protection of
FTIR spectroscopy, and FTIR could also be used to evaluate semi-quantita- cultural heritage. Chemical analysis of the
tively the degree of the degradation of the cellulose. artworks can be of great value prior to any
The wallpaper industry was a very prosperous sector in the nineteenth restoration process, even though it can be
century that followed the same pattern of the other crafts from the same focused on many other aspects. For
century, applying the new pigments available in that period. Antique example, it provides historians with very
pigments (e.g., minium, red oxides and carbon black) were determined interesting information about techniques
together with new ones, first synthesised during the nineteenth century (e.g., and materials used during a period of time
copper-arsenic pigments and ultramarine blue). or by an artist. This information can help
We observed a transition in the use of the antique pigments to the new to characterise and to understand in a
ones in the wallpaper items going through the century. The great transfor- deeper way the context in which the art-
mation of the chemical industry was clearly reflected in the evolution of the work was created. At the same time, it can
wallpaper industry during that century. be used to discover forgeries, antique
ª 2007 Elsevier Ltd. All rights reserved. copies or later re-paintings. Besides,
damage to the materials caused by the
Keywords: Artwork; Binder; Cellulose oxidation; Fourier transform infrared; FTIR;
environment or by human activities can
Pigment; Raman; Wallpaper
be ascertained only if chemical analysis is
carried out [1].
K. Castro*, A. Sarmiento, M. Pérez-Alonso, J.M. Madariaga In any case, the knowledge of the his-
Department of Analytical Chemistry, University of the Basque Country, P.O. Box. 644, 48080 torians and experts in fine arts should not
Bilbao, Spain
be dismissed. Moreover, the opinion of
E. Princi, S. Vicini, E. Pedemonte these professionals is fundamental in
Dipartimento di Chimica e Chimica Industriale, University of Genova, Via Dodecaneso 31,16146 interpreting the scientific data, so as to
Genova, Italy reduce the time and the money needed for
the analysis, so scientific studies of art-
M.D. Rodrı́guez-Laso
works must be multidisciplinary. Restorers
Department of Painting, University of the Basque Country, P.O. Box. 644, 48080 Bilbao, Spain
and curators have to explain their
requirements, and scientists have to be
*
Corresponding author. Tel.: +34 94 601 8298; Fax: +34 94 601 35 00; aware of those priorities and design all the
E-mail: qabcaork@lg.ehu.es
0165-9936/$ - see front matter ª 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.trac.2007.02.003 1
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Trends Trends in Analytical Chemistry, Vol. XX, No. X, 2007
experimentation to focus on them, including the selec- In binder analysis, chromatographic techniques have
tion of the analytical techniques. In the case of the been used successfully [8]. However, they need long,
analysis of artworks on paper support, vibrational spec- complicated sample preparation, they are destructive
troscopic techniques present some advantages over the and they can be applied to only organic compounds. For
other analytical techniques. Of all of them, infrared (IR) analysis of inorganic compounds, X-ray diffraction
and Raman should be highlighted, as the number of (XRD) has been applied, but it is destructive and needs
contributions using one or both techniques has in- sample preparation, so it is invasive and ‘‘in situ’’
creased, especially in the past decade. analysis cannot be performed; also, XRD cannot be ap-
Both techniques perform molecular analysis (i.e. they plied to organic compounds. However, recently, some
provide the information about the molecules present in portable micro-XRD instruments have presented some
the artworks, and therefore about the raw materials used interesting characteristics [9].
by the artists). This is a great advantage over the tech- By contrast, IR and Raman spectroscopies can detect
niques of elemental analysis, that quantify the individual both organic and inorganic compounds, and, in some
elements present in the samples but do not provide cases, they can provide not only molecular information
information about how those elements are linked. Ele- but also structural data, because it is possible to distin-
mental analysis has been applied, among other appli- guish anatase (TiO2) from rutile (TiO2), for example. In
cations, mainly in archaeometallurgy [2], pottery and addition, one reason for the success of vibrational spec-
stained-glass analysis [3,4], where the results are pro- troscopic techniques is that they complete analysis easily
vided in terms of oxides of the elements, but that is not at a reasonably low cost compared with other tech-
very useful in the analysis of polychromatic artwork on niques.
paper support. As Raman and IR spectroscopies are complemen-
Besides, almost all elemental techniques are destruc- tary, they have been applied simultaneously in cul-
tive and need sample preparation. In the case of Raman tural heritage [10]. Moreover, there are already
spectroscopy, non-destructive, non-invasive, ‘‘in situ’’ equipments that combine both techniques (i.e. Raman
analysis can be performed using portable fiber-optic and IR spectra can be collected from the same spot
probes. This means that the instrument can be moved to [11]). Several reviews on artwork analysis by Raman
the location where the artwork is placed and the analysis spectroscopy have been published [12–14] as well as
is achieved directly over the object. As ‘‘in situ’’ analyses some applications of FTIR spectroscopy in the field of
are totally non-destructive, there is no damage to the cultural heritage (e.g., together with XRF and Raman
artwork, and they can make as many measurements as spectroscopy) [15].
needed so that the results are very reliable. This is a Artworks on paper support are very delicate if we
great advance with regard to classical instrumentation compare them with other types of artwork, and that
that performs only a few measurements in the labora- requires new strategies of analysis based on non-
tory, sometimes with partial results (e.g., scanning destructive, non-invasive analysis, as we will show
electron microscopy with energy-dispersive X-ray anal- below. Raman spectroscopy and IR spectroscopy have
ysis (SEM-EDX), inductively coupled plasma mass spec- probably demonstrated the best characteristics for
trometry (ICP-MS), neutron diffraction, atomic achieving this aim.
absorption spectroscopy (AAS)).
Laser-induced breakdown spectroscopy (LIBS) and 1.1. Studies of artworks on paper
X-ray fluorescence (XRF) may present some interesting In IR spectroscopy, there have not been too many
characteristics but they provide only elemental infor- studies of artwork on paper support. In the most recent
mation. Giakoumaki et al. [5] presented new LIBS years, only Romero et al. [16] and Sistach et al. [17]
equipment that is combined with Raman spectroscopy to have related the use of FTIR. More recent is a report by
provide analysis at the same point. There is a complete Ferrer and Vila [18] on analysis of Spanish stamps
review of this technique applied in art and archaeology from the nineteenth century. IR was also used in
[6]. analyzing manuscripts [19], sometimes in conjunction
In many cases, artworks, such as wallpapers, comprise with visible microspectroscopy [20] or attenuated total
a superimposition of coloured layers on a paper support. reflectance (ATR) and a diamond cell [21]. The char-
This characteristic is very critical when elemental anal- acteristics of IR make it difficult to analyze manu-
ysis is done. For example, XRF could be a very interest- scripts, from which it is almost impossible to take a
ing technique because there are available arrangements sample to make a pellet and acquire a standard FTIR
that are portable and non-destructive [7]. Nevertheless, spectrum.
when applied on multilayered artworks, due to the By contrast, Raman spectroscopy has become in a
penetration power of the beam, data from more than one very powerful tool in the analysis of artworks on paper.
layer can be recorded in the same spectrum, so the It was interesting to see the review by Vandenabeele and
results could be very difficult to interpret. Moens [22] on the analysis of illuminated manuscripts
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by Raman spectroscopy assisted sometimes with XRF The most important period in the use and the design
analysis (e.g., to obtain the impurity pattern in order to of wallpapers started in the second half of the eigh-
characterise the source of the pigments). Other inter- teenth century, finishing in the middle of the nineteenth
esting works have been published on Raman charac- century. Wallpaper manufacture involved superposing
terisation of manuscripts [23,24], antique bibles [25], paint layers until the whole drawing was composed
Persian poetry books [26], postage stamps [27] and using the blocks of wood in which the drawing was
lithographs [28]. engraved, so it was a multilayer work (block printing).
An interesting work that sums up the interdisciplinary To accomplish a wallpaper, more than 40 different
nature of artwork analysis as well as a real application of blocks could be needed, depending on the complexity of
Raman spectroscopy in the design of strategies of con- the drawing and the numbers of colours and shades it
servation of damaged works is that by D. Wise et al. [29]. had. Moreover, some scenic wallpapers needed more
The authors discuss the benefits that a detailed knowl- than 1000 wood-blocks and more than 100 colours or
edge of inks and pigments can have for both conserva- shades [38].
tors and curators. Several works have been published on The technical improvements in the manufacturing of
wallpaper by Meharg [30] on the manufacturer William modern continuous paper by Louis Robert and the use
Morris, and there is also a paper by Welsh [31]. More of cylinders in the printing process (engraved cylinder
recent are works on pigment characterisation of scenic invented by Dickinson) was of great importance from
wallpapers and other historic wallpapers from the the second third of the nineteenth until the beginning
nineteenth century [32–35]. of the twentieth century. They provided the possibility
The characterisation of organic binders is crucial since of making cheaper wallpapers, allowing manufacturers
it is a source of important information for both recon- to use larger formats. However, their quality decreased,
structing the working techniques used in a particular as they were more fragile and more difficult to pre-
artwork and defining a programme for restoration and serve.
conservation of the work itself. Besides, many processes
of deterioration are due to the greater reactivity of or-
2. Cases studied
ganic binders compared to inorganic pigments also
found. Binders on paper supports have so far been
We considered several wallpapers from throughout
determined in few studies. However, several authors
nineteenth century in order to view differences and
have used FTIR to determine binders in artwork on other
similarities with respect to their chemical composition.
kinds of support [36].
Table 1 summarises the artworks from the beginning,
middle and the end of the nineteenth century involved in
1.2. Decorative wallpapers the study. We characterized some of them for the first
In the sixteenth century, society underwent a sharp time but we included other samples previously studied
change, when dealers and sellers established a new because we determined new materials.
social class – the bourgeoisie – who had access to wealth Wallpapers can be classified in three groups:
and built their own houses. In Europe, there was a boom (1) old (until ca. 1832–35), using block-printing on
in all popular arts. In many cases, the bourgeoisie could little sheets of hand-crafted paper;
not decorate their houses with expensive marbles, (2) transition (from ca. 1832 to ca. 1850), using little
tapestries or velvet. By contrast, they ordered from sheets of paper and block-printing, but introducing
craftsmen to manufacture painted papers resembling all new synthetic pigments and continuous paper; and,
expensive decorations mentioned above, trying to (3) modern (from ca. 1850) using engraved cylinders
imitate the luxury of the nobility [37]. on continuous paper.
Table 1. List of the artworks considered in this article
Title Date Manufacturer Type Ref.
Les Monuments de Paris (wallpaper) 1812–1814 Dufour et Leroy (Paris) Old [34]
Chasse de Compiègne (wallpaper) 1812–1815 Jacquermart et Bernard (Paris) Old [35]
Angels (border wallpaper) 1812–1815(doubts) Jacquermart et Bernard (Paris) Old This article
Naval battle (wallpaper) 1828–1840(doubts) Unknown Transition [33]
Santa IsabelÕs factory wallpaper (I) 1846–1850 Santa Isabel factory (Spain) Modern [32]
Santa IsabelÕs factory border wallpaper (II) 1846–1850 Santa Isabel factory (Spain) Modern This article
First generation of pigmented wallpapers 1850–1870(doubts) Unknown Modern [39]
Oil on paper 1880–1900(doubts) Unknown Modern This article
Low-cost pigmented wallpapers 1880–1900(doubts) Unknown Modern This article
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Table 2. Summary of the pigments found in the samples analysed
Les Chasse de Angels Naval Santa Santa First- Oil on Second-
Monuments Compiègne (border Battle Isabel (I) Isabel (II) generation wallpaper generation
de Paris wallpaper) pigmented pigmented
wallpaper wallpaper
Year 1812–1814 1812–1815 1812– 1828–1840 1846–1850 1846–1850 1850– 1880– 1880–
1815(doubts) 1870(doubts) 1900(doubts) 1900(doubts)
OLD MATERIALS
ARTICLE IN PRESS
Yellow iron oxide Antique X X
Lead white Antique X X X
Calcium carbonate Antique X X X X X X X X X
Gypsum Antique X X X X
Massicot Antique X
Minium Antique X X X X X X X
Vermilion Antique X X X X
Brown earths Antique X X X X X
Carbon/bone black Antique X X X X X X X X X
Red iron oxide Antique X X X X X
Lead tin yellow type II 1300 X X
Trends in Analytical Chemistry, Vol. XX, No. X, 2007
Prussian blue 1704 X X X X X X X X
NEW MATERIALS
ScheeleÕs green 1778 X ? X
Brochantite c.a. 1800 X
Chrome yellow 1803–1818 X X X X X X
Chrome orange 1809–1818 X
Barium sulphate 1810–1820 X X X X X
Emerald green 1814 ? X
Ultramarine blue 1828–1830 X X X
Synthetic organic pigments 1850–2006 XARTICLE IN PRESS
Trends in Analytical Chemistry, Vol. XX, No. X, 2007 Trends
3. Results and discussion source was available when Naval battle and pigmented
wallpapers were manufactured.
3.1. Wallpaper manufacturing materials (Industrial It is curious how, in old wallpapers, we determined
archaeology) only iron oxides as the yellow pigment, whereas, in the
Studies of wallpaper samples from different periods of the other samples, only chrome yellow was found. This is a
nineteenth century demonstrate how the wallpaper- clear example of how cheap pigments of industrial origin
manufacturing industry was incorporating the new were incorporated into the palette, and that there was
pigments available at that time, as well as their period of always a period of time before introducing pigment.
introduction (see Table 2). This is very important be- Chrome yellow was discovered in 1797, but it was not
cause the chemical industry underwent huge develop- recognised as a pigment until ca. 1803. It is supposed
ment during the nineteenth century, so pigments used that the industrial production of the pigment started ca.
were mainly of industrial origin instead of being hand- 10 years later with the discovery of mineral chromite.
crafted on a small scale. Interestingly, the Santa Isabel This is why chrome yellow was not found in the samples
Wallpaper Factory (1845) was set up next to a pigment from 1812 but was found in the modern samples. As
factory [33]. Pigment analysis has been performed happened with the yellow chrome pigment, we
according to the methodology described elsewhere [34] determined chrome orange only in the modern samples
using several databases of spectra [40,41]. (Naval battle).
From Table 2, interesting differences can be noticed The green colour is related to blue and yellow pig-
among the pigments used in the wallpapers. Regarding ments. In almost all samples, the green colour was a
the white pigments, we must point out that lead white mixture of a blue and a yellow pigment, and even to a
was determined in the samples only from 1812. By complex mixture of yellow, blue and green pigments
contrast, in the most modern wallpapers, calcium car- (e.g., Prussian blue was found mixed with chrome
bonate, gypsum and barium sulphate were found. Zinc yellow in the most modern samples (Santa Isabel, Naval
white and titanium white replaced lead white at the end battle and first-generation pigmented wallpapers)). This
of the nineteenth century, because of the high toxicity of mixture could be considered a green pigment, because,
lead white, even though they had been available since at the beginning of the nineteenth century, there was a
the middle of the nineteenth century. However, in the pigment sold as chrome green that was a mixture of
most modern wallpapers analyzed, zinc white and tita- Prussian blue and chrome yellow. However, in first-
nium white were not found. Calcium carbonate and generation pigmented wallpapers, we also identified a
gypsum were also found in the samples from 1812, and mixture of ultramarine blue and chrome yellow.
they must be seen as extenders and fillers of the other The green colour analyzed in the sample from Santa
pigments. By contrast, barium sulphate was not found in Isabel Factory (I) needs further explanation. We ob-
the samples from 1812. Natural barium sulphate was served severe oxidation of the paper below the green
introduced as an artistsÕ material in 1782 but it was not colour. This degradation was not visible in the blue
used extensively until the introduction of the synthetic (Prussian blue) and yellow (chrome yellow) areas, so
barium sulphate in 1810–20, so this finding agrees with presence of these pigments alone could not explain this
data found in literature. oxidation process. A third pigment had to be present.
Barium sulphate has been related to the presence of Later analysis of this colour, carried out with a por-
synthetic organic pigments in some of the most modern table XRF instrument, revealed a massive presence of
samples (first-generation pigmented wallpapers), as well arsenic and copper. Unfortunately, no Raman or FTIR
as an extender. However, in the Raman analysis of the spectral record was obtained, so we could only suggest
sample from Santa Isabel Factory (I), we found that what could be the pigment present. In the literature, we
BaSO4 had been used as the white pigment for the found two different kinds of arsenic-copper pigment –
background of the wallpaper. ScheeleÕs green (copper arsenate) and emerald green
Blue, green and yellow pigments provided very valu- (copper aceto-arsenite). ScheeleÕs green was found in Les
able information about the transformations in the Monuments de Paris, but, in this case, we did not ob-
manufacturing processes of wallpapers, and therefore in serve any degradation, even though the state of con-
the chemical industry. In the samples from 1812 (Table servation of the sample was much worse than the
1), only Prussian blue (a very common pigment syn- sample from Santa Isabel Factory (I). We postulated that
thesized since the middle of the eighteenth century) was the pigment present in the sample from the Santa Isabel
found as the blue pigment, whereas, in some of the most Factory (I) could be at least emerald green, that being
modern wallpapers, artificial ultramarine blue was found the acetate anion responsible for the cellulose-oxidation
together with Prussian blue. We need to take into ac- process, catalyzed by the presence of copper ions [42].
count that ultramarine blue was not produced as a To obtain Raman evidence of the presence of emerald
pigment in factories until 1828–30, so a plentiful, cheap green in the sample from Santa Isabel Factory (I), we
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analyzed a second sample from the same factory with the not used in the years in which the wallpaper was
same oxidation process – border wallpaper Santa Isabel manufactured, so it can be considered a late, or out of
Factory (II) found in the same room. As can be seen in time, use of it. It would also be very important to analyse
Fig. 1, we could demonstrate the presence of emerald other known artworks from these manufacturers (Jac-
green and ScheeleÕs green in the green colours together quemart et Bernard) in order to check if this pigment
with Prussian blue and chrome yellow, that being the was also present. We found the same pigment in the
emerald-green pigment responsible for the oxidation yellow areas of the Angels wallpaper. Both samples ap-
process. peared in the same room, but, whereas Chasse de
In Les Monuments de Paris, the green colour was a Compiègne is catalogued and the manufacturer is
mixture of Prussian blue and ScheeleÕs green in different known, the sample of the Angels is completely un-
proportions, whereas in Chasse de Compiègne, Prussian known. The strange presence of this pigment (lead-tin
blue was mixed with yellow iron oxide. Besides, in yellow type II) could suggest that the manufacturer of
Chasse de Compiègne, we found lead-tin yellow type II both samples was the same.
together with basic copper sulphates brochantite and Finally, other pigments such as minium, vermilion,
antlerite. In this case, antlerite might be considered a brown earths, carbon black and red iron oxide have been
degradation product of brochantite, as discussed else- found without distinction in all samples along the cen-
where [35]. tury. These pigments are known since antique and are
ScheeleÕs green was available from the end of eigh- used even nowadays.
teenth century, but it was used only until the beginning
of nineteenth century because of its high toxicity. It 3.2. Binders in wallpapers
could be very interesting to analyse other artworks from We carried out FTIR analysis of the binders after solvent
these manufacturers (Dufour et Leroy and Santa Isabel extraction (with dicloromethane and water), according
Factory) to check the involvement of this pigment in to the methodology described [44]. While the spectra
their production. obtained after the extraction with dicloromethane did
In the same way, emerald green was extensively used not give any signal, the spectra obtained from the
during the nineteenth century with very adverse con- aqueous extract of wallpapers Santa Isabel, Les Monu-
sequences in the health of people and wallpaper-manu- ments de Paris and Chasse de Compiègne presented the
facturing-industry workers [30]. characteristic bands of Arabic gum (Fig. 2). The spec-
Lead tin yellow type II was surprisingly determined in trum of a polysaccharide has a strong broad band at
Chasse de Compiègne. According to Kuhn [43], it was about 1080 cm 1 due to C-O. Besides, the C-H stretches
Figure. 1. Raman spectra of the green area where oxidation was observed (Em: Emerald green; Sch: ScheeleÕs green; ChY: Chrome yellow;
Pr: Prussian blue). In the box at the top, the spectral window around 2000 cm 1 is shown with the characteristic bands of Prussian blue.
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Figure 2. FTIR spectra of the aqueous extracts from the wallpapers Santa Isabel, Les Monuments de Paris and Chasse de Compiegne.
tend to be weak and poorly resolved (around 2920 cm 1 preparation, a very rich pictorial layer was elaborated
and 2850 cm 1) and are very similar to those from with a drying oil.
animal glue, for which they are better resolved, and Oil spectra contain a medium, sharp carbonyl band at
glues do not present the broad band at 1080 cm 1. around 1750–1740 cm 1, as observed in the organic
However, there were a displacement in the band extract. It is the only natural organic binder that has an
located at 1616 cm 1 associated with carboxyl groups intense carbonyl band in this region. Besides, the CH2
and intermolecular water (appearing at 1647 cm 1in stretches (2966 cm 1, 2925 cm 1 and 2854 cm 1) of
these wallpapers) and there was a shoulder located at the sample and the standard coincide. However, there
1558 cm 1. This seemed to indicate that the binder of are important differences in the region of the fingerprint
the three wallpapers was a mixture of Arabic gum and a (1600–400 cm 1) as well as in the area of the olefinic
proteinaceous binder. Fourier self-deconvolution was C‚C–H bond. The intensity of this last band (centered
used to study the components of the peak at 1647 cm 1, on 3020–3010 cm 1) depends on the dryness of the oil,
revealing the presence of absorption bands due to amide and, in well-dried oils, this band will be very small or
I (1650 cm 1) and amide II (1550 cm 1), together with even disappear. This was the case of our real sample,
the band at 1616 cm 1 of carboxyl groups in the where the oil had dried. The same occurs in the region of
spectra, confirming again the presence of both types of the fingerprint, where the chemical changes that take
binder. place during the drying of the oil cause changes in the
However, it was necessary to know the layers from spectrum.
which both binders come, or if they where mixed to- The spectrum of the aqueous extract reveals the
gether. We analyzed a sample containing only the pic- presence of gypsum hemihydrate (bands at 3609, 3554,
torial layer after aqueous extraction showing only the 1547, 661 and 601 cm 1). This calcium sulphate was
characteristic peaks of Arabic gum without any kind of applied using animal glue as binder. Characteristic bands
displacements or shoulders (i.e. the pictorial layer was of the binder are present in the spectrum at 1650 cm 1
made with Arabic gum over a paper support previously and 1550 cm 1 due to amide I and amide II bonds,
coated with animal glue). This preparation layer was together with the well-resolved C-H stretches around
quite usual in hand-made wallpapers in the nineteenth 2920 cm 1 and 2850 cm 1.
century. To confirm the composition of the background layer,
By contrast, FTIR analysis after dicloromethane we obtained a spectrum of an aqueous extract of a non-
extraction of one of the specimens revealed an unex- pigmented area, and obtained the same results, but, in-
pected way of manufacturing a painted paper. This stead of obtaining gypsum hemihydrate, we detected
wallpaper contains a preparation layer that comprises a anhydrite. Apparently, those compounds are not the
mixture of gypsum and animal glue. Then, over this original materials used in the preparation layer because
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both are insoluble. However, if gypsum was the original Indeed, FTIR analysis carried out on the Santa Isabel
compound, a little calcium and sulphate could be dis- wallpaper showed the characteristic band of carbonyl
solved in the aqueous extract. After evaporating the stretching in line with the oxidised regions of the sample.
water to obtain the pellet to be analysed in the FTIR The FTIR analysis on the Whatman paper oxidised
equipment, we re-precipitated calcium and sulphate with sodium metaperiodate allowed us to perform a
ions. Depending on the final degree of moisture after semi-quantitative evaluation of the degree of oxidation of
evaporation step, we could obtain gypsum hemihydrate cellulose, calculating the ratio (R) between the absor-
or anhydrite, so the preparation layer was definitely bency stretching bands of the C‚O at 1720 cm 1 and
formed with gypsum and animal glue. CH2 at 2900 cm 1. R increases with time and concen-
tration, and even short oxidation times are sufficient to
3.3. Degree of cellulose oxidation induce noticeable degradation of cellulose. In this way, a
It is well known that photo-degradation, acid hydrolysis, calibration curve can be obtained for use in analyzing
oxidation by atmospheric oxygen and biodeterioration unknown aged paper samples. In this case, after
are the main factors that act on cellulose, causing its recording the spectrum, the ratio R is calculated and is
alteration. FTIR spectroscopy represents a useful tool to fitted to the calibration curve in order to have an idea of
monitor the behaviour of cellulose when it undergoes the degree of oxidation of cellulose. For example, the
the oxidative attack. This oxidation involves the primary analysis carried out on the Santa Isabel wallpaper (oxi-
and secondary hydroxyl groups of the pyranose ring, dation due to the presence of copper pigments) showed a
leading to the formation of carbonyl and carboxyl value of R about 1.2, indicating strong oxidation of the
groups. Sometimes, the progressive fragmentation of the paper support.
cellulose chain is observed, so the degree of polymeri-
sation (DP) and the mechanical strength are noticeably
reduced [45]. 4. Comparative analysis
To investigate the behaviour of cellulose at different
levels of oxidation in the laboratory, we undertook an It is interesting to compare the results obtained from the
artificial treatment by oxidising the Whatman paper analysis of the wallpapers (Table 2) with the materials
with sodium metaperiodate at two different concentra- found in other artefacts from the same century, in order
tions, 0.1 M and 0.4 M, for different times. Periodate to check if there are differences or if there are the same
oxidation is a highly specific reaction to convert 1,2- patterns with regard to the materials used and the
dihydroxyl groups into aldehyde groups, without sig- introduction of new materials first synthesised in the
nificant side reactions [46]. When applied to glucose in nineteenth century.
the cellulose chain, this reaction cleaves the C2–C3 Comparing Tables 2–4, we can notice that, until
bond, in according to the mechanism of Malaprade 1830–40, the materials determined in the samples cor-
reaction [47], leading to the formation of dialdehyde respond to pigments known since antiquity, even
cellulose (DAC) [48]. Increasing the reaction time and though, by that time, others had already been artificially
the methaperiodate concentration, the degradation is synthesised and were available. In contrast, in the
more considerable. second third of the century, new materials were intro-
The oxidation reaction leads to the presence of two duced into the palette of artists and artisans. It seems
characteristic bands of DAC in the 1720 cm 1 and that there is always a period of some years after new
880 cm 1 regions of the spectrum and they increase materials are available industrially (i.e. cheaper and
from a small shoulder to a distinct band, increasing the easier to obtain) before they are incorporated into the
oxidation level giving the sharp band at 1720 cm 1 colour palette and intensively used, as in the case of
characteristic of carbonyl groups [49]. wallpapers. However, some early use of some new
The band of the unbonded water (1635–1670 cm 1) material can be possible, as well as later use of some
is very close to the bands of the carbonyl groups, which antique pigments.
it can hide. In addition, identification of the aldehydic In general, the materials found in the samples in-
group is very difficult, since DAC can exist in partially or volved in this study (wallpapers) were the common ones
completely hydrated forms, as hemiacetal or hemialdale, used during the nineteenth century. Antique pigments
that do not present the classical peak of aldehydic car- (e.g., yellow and red iron oxide, lead white, minium,
bonyl, so the thermal treatment of KBr disks before FTIR carbon black, calcium carbonate, vermilion, brown
analysis is fundamental to reducing the amount of water earths, and natural organic pigments) together with
in the cellulose. Prussian blue were used throughout the century in all
From these considerations, it is clear that the oxidative kinds of artefact, even though new materials were
phenomena can be easily monitored with FTIR analysis, available by that time (e.g., cadmium pigments, and
evaluating qualitatively if the oxidation reaction leads to yellow and red synthetic organic pigments). It is true
the formation of carbonyl groups in the cellulose chain. that these new pigments were not lightfast, but they did
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Table 3. Summary of the pigments found in artifacts on paper from nineteenth century
Flora Thai 1 Hawaiian Mauritius Thai 2 manuscript Thai 3 manuscript Wallpapers Lithographs
Danica manuscript stamps stamps
Technique Raman Raman Raman Raman Raman Raman XRF Raman
Ref. [50] [51] [52] [28] [51] [51] [53] [28]
Year End 18th– ca. 1800 1851–1852 1847–1862 1880 ca. 1900 Second half of 19th Second half of 19th
Beginning
19th
OLD MATERIALS
Lead white Antique X X X X
Yellow iron oxide Antique X
Calcium carbonate Antique X X X
ARTICLE IN PRESS
Gypsum/Anhydrite Antique X
Minium Antique X X X X X X X
Vermilion Antique X X X X X X X
Brown earths Antique X
Green earths Antique X
Carbon black Antique X X X X X X
Red iron oxide Antique X X
Orpiment Antique X X X
Massicot/Litharge Antique X X
Natural indigo Antique X
Natural organic pigments Antique X X
Silver/Gold Antique X
Prussian blue 1704 X X X X X
NEW MATERIALS
ScheeleÕs green 1778 X
Atacamite 1801 X
Chrome yellow 1803–1818 X X X X
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Chrome orange 1809–1818 X X
Barium sulphate 1810–1820 X X
Cadmium yellow 1818 X
Ultramarine blue 1828–1830 X X X X X
Synthetic organic pigments 1850–2006 In forgeries X
Indigo blue 1880 X
Phthalocyanine pigments 1936 Impurity In forgeries X
Trends
9ARTICLE IN PRESS
Trends Trends in Analytical Chemistry, Vol. XX, No. X, 2007
Table 4. Summary of the pigments found in other artifacts from nineteenth century
French miniatures Greek icon Monet painting Pigment Arnold Böcklin
collection
Technique Raman Raman SEM-EDS XRD, Spot test, XRD, Spot test, Emission
Emission Spectroscopy,
spectroscopy, Microscopy
Microscopy observations
observations
Ref. [54] [54] [55] [56] [57]
Year 18th–19th century Early 1800s 1887 19th century 1827–1901
OLD MATERIALS
Yellow iron oxide Antique X X
Lead white Antique X X X X X
Calcium carbonate Antique X
Gypsum/Anhydrite Antique X X X
Minium Antique X X X
Vermilion Antique X X X X
Brown earths Antique X X X
Green earths Antique X X
Carbon/bone black Antique X X X
Red iron oxide Antique X X X
Orpiment Antique X X X
Massicot/Litharge Antique X X
Natural indigo Antique X
Natural organic pigments Antique X X X X
Manganese black Antique X
Azurite Antique X
Realgar Antique X
Silver/Gold Antique X X X
Verdigris Antique X X
Smalt Antique X X
Naples yellow Antique X X
Prussian blue 1704 X X X
NEW MATERIALS
ScheeleÕs green 1778 ?
Cobalt green 1780 X
Zinc white 1780 X
Brochantite c.a. 1800 X
Cobalt blue 1804 X X
Zinc yellow 1809 X
Chrome oxide 1809 X
Chrome yellow 1803–1818 X X X X
Barium sulphate 1810–1820 X X
Emerald green 1814 ? X X X
Cadmium yellow 1818 X X
Cerulean blue 1821 X
Ultramarine blue 1828–1830 X X X
Viridian 1850 X X
Synthetic Indigo blue 1880 X
Synthetic organic pigments 1850–2006 X
not follow the pattern of other new pigments (e.g., show that it was found even in samples from the second
chrome yellow, chrome orange or barium sulphate) that half of the nineteenth century. This is not strange, be-
were incorporated into the colour palette in a very sort cause, even though other white pigments where avail-
period of time after their date of synthesis. Orpiment, able, lead white remained throughout the whole
another traditional yellow pigment, appears throughout century.
the century, although it was not found in any of the With the synthesis of Prussian blue, the traditional old
wallpapers analysed. In the wallpapers, lead white was blue pigments (azurite, smalt, and lapislazuli) almost
found only in the oldest samples, whereas Tables 3 and 4 disappeared from the colour palette, but smalt blue still
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Trends in Analytical Chemistry, Vol. XX, No. X, 2007 Trends
appeared in two collections of pigments [56,57]. The that used paper as the support (e.g., playing cards)
introduction of artificial ultramarine blue was introduced into their colour palette the same or other
noteworthy, if we take into account that other blue pigments.
pigments synthesised in the same period (e.g., cobalt By using IR spectroscopy, we have shown how almost
blue and cerulean blue) did not make the same impact as all the wallpapers were made with an Arabic gum over a
ultramarine blue. After ultramarine blue was synthe- paper coated with a proteinaceous binder. However, one
sized, the hegemony of Prussian blue ended. This situa- of the specimens analysed was made with an oil tech-
tion remained until the introduction of phthalocyanine nique directly over the cellulosic support. This is very
blue at the beginning of the nineteenth century. interesting because, on the one hand, we have demon-
In almost all cases, green colour is obtained by mixing strated that, with the tested methodology, we can
different pigments, blue and yellow mainly, but some- determine different kinds of binder, and on the other
times, a green pigment can be present (e.g., in one of the hand, we discovered an oil-on-paper technique that is
Santa Isabel Factory wallpapers, the green colour was a not at all common. We need to take into account that
complex mixture of Prussian blue, chrome yellow, the oil is very acidic and it degrades and damages the
emerald green and ScheeleÕs green). Even though this cellulosic support quickly and extensively
mixture might seem strange, Burgio et al. [54] found a To complete the analysis, we have presented a simple
very similar mixture of pigments in some French min- method to get to know the degree of oxidation of the
iatures from the eighteenth-to-nineteenth century. cellulosic support. We were able to establish that the
Unfortunately, they can not confirm which pigments, oxidation due to the presence of copper pigments was
emerald green and/or ScheeleÕs green, are present. very great in the wallpaper sample from the Santa Isabel
Besides, they do not report any deterioration process. Factory.
Arsenic green pigments were extensively used during Taking into account all the results and the expertise
the nineteenth century, if we take into account the that we acquired, it is possible to state that vibrational
notable occurrence of emerald green and ScheeleÕs spectroscopic techniques present good advantages and
green (Tables 2–4), even though they were very toxic. qualities in analyzing artworks. The possibility of per-
By contrast, other new pigments synthesised in the forming non-destructive analysis as well as the capabil-
nineteenth century (e.g., cobalt green, chrome oxide ity of determining both organic and inorganic
and viridian) rarely occurred in artifacts in the nine- compounds make FTIR and Raman spectroscopy very
teenth century. Besides, antique green pigments (e.g., suitable for use in the field of cultural heritage.
verdigris and green earths) were replaced by the new
ones.
With regard to the organic pigments, we can say that 6. Future work and improvements
natural organic pigments were used in the samples from
the beginning of the nineteenth century, whereas syn- With the experience acquired during this work, we can
thetic organic pigments started to be used at the end of make several comments about future work and research
the nineteenth century (e.g., Wise and Wise [29] found guidelines. In cultural heritage, the sample under study
aniline dyes in a sketchbook by Tommy McRae from the is always a complicated matrix of several materials (e.g.,
1880s). In some cases, the determination of synthetic substrate, binding media and pigments). In pigment
organic pigments was the clue to discovery of forgeries, analysis by Raman spectroscopy, the analysis of the
later copies or reproductions [52]. It is significant the spectra performed peak-by-peak is usually easy and does
case of indigo blue, a natural organic pigment was not present special difficulties. However, FTIR analysis of
replaced by synthetic one around 1880–97. binders presents many problems, it is tedious and does
not always give good results.
To assist the visual examination of spectra, a model
5. Conclusions based on the chemometric treatment of the data should
be used, at least for binder analysis. Although there are
By using direct, non-invasive and non-destructive many statistical techniques available for identifying the
Raman analysis, this work has shown which materials major features responsible for defining ‘‘pattern recog-
were used in the manufacturing process of wallpapers nition’’ in a sample, the most common technique is
during the nineteenth century, the beginnings of the principal components analysis (PCA). This technique
industrial era, also reflecting the beginning of the mod- can often be so efficient in reducing the dimensionality of
ern chemical industry. It would be very interesting to analytical data so that it can provide an immediate vi-
study other wallpapers of the same century from other sual indication of patterns within data. We have at-
countries to see if they used the same pigments in the tempted some chemometric analysis of the spectra that
manufacturing process. It could also be very interesting allows differentiation between the five families of binders
to study how, during the same century, other industries under study (gums, glues, casein, oils and varnish).
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Trends Trends in Analytical Chemistry, Vol. XX, No. X, 2007
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This work was partially funded by the European Project (2004) 781.
PAPERTECH (INCO-CT-2004-509095). K. Castro is [24] M. Clarke, Stud. Conserv. 49 (2004) 231.
grateful to the Ministry of Education and Science for his [25] T.D. Chaplin, R.J.H. Clark, D. Jacobs, K. Jensen, G.D. Smith, Anal.
contract at the UPV/EHU (PTA 2003-02-00050). Chem. 77 (2005) 3611.
A. Sarmiento is grateful to Ministry of Education and [26] R.J.H. Clark, S. Mirabaud, J. Raman Spectrosc. 37 (2006) 235.
[27] T.D. Chaplin, A. Jurado-Lopez, R.J.H. Clark, D.R. Beech, J. Raman
Science for his pre-doctoral grant. The access to the Spectrosc. 35 (2004) 600.
wallpaper samples is grateful acknowledged to the Dip- [28] K. Castro, P. Vandenabeele, M.D. Rodrı́guez-Laso, L. Monees,
utación Foral de Álava, Ikastola Almen, Barona family J.M. Madariaga, Anal. Bioanal. Chem. 379 (2004) 674.
and Diputación Foral de Guipuzcoa. The authors also [29] D. Wise, A. Wise, J. Raman Spectrosc. 35 (2004) 710.
want to thank the Department of Inorganic Chemistry [30] A. Meharg, Nature (London) 423 (2003) 688.
[31] F.S. Welsh, Microscope 49 (2001) 35.
and the Department of Physical-Chemistry from UPV for [32] K. Castro, M.D. Rodriguez-Laso, L.A. Fernández, J.M. Madariaga,
letting them use FTIR equipment as well as Peter Van- J. Raman Spectrosc. 33 (2002) 17.
denabeele and Luc Moens from Ghent University for all [33] K. Castro, M. Pérez-Alonso, M.D. Rodrı́guez-Laso, J.M. Madariaga,
their support. Spectrochim. Acta, Part A. 60 (2004) 2919.
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[34] K. Castro, M. Pérez, M.D. Rodriguez-Laso, J.M. Madariaga, [58] C. Ricci, I. Borgia, B.G. Brunetti, C. Miliani, A. Sgamellotti,
J. Raman Spectrosc. 35 (2004) 704. C. Seccaroni, P. Passalacqua, J. Raman Spectrosc. 35 (2004)
[35] K. Castro, M. Pérez-Alonso, M.D. Rodrı́guez-Laso, N. Etxebarria, 616.
J.M. Madariaga, Anal. Bioanal. Chem. 387 (2007) 847. [59] K.S. Andrikopoulos, S. Daniilia, B. Roussel, K. Janssens, J. Raman
[36] M.T. Doménech-Carbo, A. Doménech-Carbo, J.V. Gimeno-Adel- Spectrosc. 37 (2006) 1026.
antado, F. Bosch-Reig, Appl. Spectrosc. 55 (2001) 1590. [60] M. Schreiner, B. Fruhmann, D. Jembrih-Simburger, R. Linke,
[37] L. Hoskins, The Papered Wall, Thames and Hudson, London, UK, Powder Diffr. 19 (2004) 3.
1994.
[38] O. Nouvel, French Scenic Wallpaper, Musée des Arts Décoratifs, K. Castro is a Doctor in Analytical Chemistry and he is engaged in the
Flammarion, Paris, France, 2000 1795–1865. Department of Analytical Chemistry, University of the Basque Country,
[39] K. Castro, P. Vandenabeele, M.D. Rodrı́guez-Laso, L. Monees, Bilbao, Spain, on a research project funded by the European Commis-
J.M. Madariaga, Spectrochim. Acta, Part A. 61 (2005) 2357. sion (EC). He worked at the Guggenheim Museum, Bilbao, Spain, in
[40] K. Castro, M. Pérez, M.D. Rodriguez-Laso, J.M. Madariaga, Anal. 1999 while he finished his studies in analytical chemistry. His research
Chem. 75 (2003) 214A. focuses on XRF, Raman and IR spectroscopy applied to artwork
[41] K. Castro, M. Pérez-Alonso, M.D. Rodriguez-Laso, L.A. Fernandez, analysis.
J.M. Madariaga, Anal. Bioanal. Chem. 382 (2005) 248.
[42] V. Kireyeva, Restaurator 16 (1995) 86. A. Sarmiento is a Ph.D. Student in the Department of Analytical
[43] H. Kühn, in: A. Roy (Editor), ArtistsÕ Pigments: a Handbook of Chemistry and he is working on the determination of binders and other
their History and Characteristics, vol. 2, Oxford University Press, organic material in artworks by using IR spectroscopy, chemometrics
Oxford, UK, 1997, p. 83. and gas chromatography.
[44] A.Sarmiento, M. Maguregui, M. Pérez-Alonso, M.D. Rodrı́guez-
Laso, J.M. González-Cembellı́n, K. Castro, J.M. Madariaga, Proc. M. Pérez-Alonso is a Doctor in Analytical Chemistry and her research
16th Int. Meeting Heritage Conservation, Valencia, Spain, Novem- involves analytical methodologies in the restoration of buildings and
ber 2006, Universidad Politécnica de Valencia, Valencia, Spain. artworks.
pp. 1989.
[45] S. Vicini, E. Princi, G. Luciano, E. Franceschi, E. Pedemonte, M.D. Rodrı́guez-Laso is an Associate Professor in the Department of
D. Oldak, H. Kaczmareck, A. Sionkowska, Thermochim. Acta 418 Painting. Her research interests centre mainly on the restoration of
(2004) 123. artworks on paper (e.g., wallpapers, books and prints).
[46] U.J. Kim, S. Kuga, M. Wada, T. Okano, T. Kondo, Biomacromol-
ecules 1 (2000) 488. J.M. Madariaga is Professor in the Department of Analytical Chem-
[47] P. Cremonesi, B. Focher, L. DÕAngiuro, Cell. Chem. Technol. 6 istry. His research focuses on artwork analysis, environmental analysis,
(1972) 145. and the design of analytical procedures to regenerate polluted sites
[48] A.J. Varma, M.P. Kulkarni, Polym. Deg. Stab. 77 (2002) 25. (soils, sediments, wastes and buildings) with authentic raw materials.
[49] P. Calvini, A. Gorassini, Restaurator 23 (2002) 48.
[50] L. Burgio, R.J.H. Clark, H. Toftlund, Acta Chem. Scand. 53 (1999) E. Princi is a Doctor in Industrial Chemistry; she is working on
181. tailoring, synthesis and application of polymeric materials in the
[51] L. Burgio, R.J.H. Clark, P.J. Gibbs, J. Raman Spectrosc. 30 (1999) field of conservation of cultural heritage.
181.
[52] T.D. Chaplin, R.J.H. Clark, D.R. Beech, J. Raman Spectrosc. 33 S. Vicini is a Researcher at the Dipartimento di Chimica e Chimica
(2002) 424. Industriale. Her activity is focused on polymer science and its appli-
[53] A. Meharg, Spectrosc. Eur. 16 (2004) 16. cation in different fields, such as artwork conservation and the prepa-
[54] L. Burgio, K. Melessanaki, M. Doulgeridis, R.J.H. Clark, D. Anglos, ration and characterisation of antifouling paints and coatings.
Spectrochim. Acta, Part B 56 (2001) 905.
[55] P. Dredge, R. Wuhrer, M.R. Phillips, Microsc. Microanal. E. Pedemonte is a retired Professor of Industrial Chemistry of the
Microstruct. 9 (2003) 139. University of Genova. The main topics of his research are the science
[56] E.L. Richter, H. Härlin, Stud. Conserv. 19 (1974) 76. and technology of polymeric materials and chemistry for the conser-
[57] E.L. Richter, H. Härlin, Stud. Conserv. 19 (1974) 83. vation of cultural heritage.
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