Applications of Spectral Analysis Methods in the Restoration
and Preservation of Some Easel Paintings from
Romanian Museum Collections
POLIXENIA GEORGETA POPESCU 1,2,*, CRISTIAN ENACHE-PREOTEASA3, FLORIN DINU BADEA1
1
University “Politehnica” of Bucharest, Faculty of Applied Chemistry and Material Science, 313 Splaiul Independenþei,
060042, Bucharest, Romania
2
Brukenthal National Museum, 4-5 Piaþa Mare, 550163, Sibiu, Romania
3
Central Phytosanitary Laboratory, 11 Voluntari Blv., 077190, Voluntari, Romania
In this study the analysis of the painting medium (vegetable oil based binder) from nine canvas paintings,
belonging to the national cultural heritage is presented. The paintings were investigated and restored in the
Brukenthal National Museum, Sibiu laboratories. Seven paintings belong to the Brukenthal Painting Galleries
and two artworks belong to other collections. The nine artworks are painted in oil or mixed oil-tempera
techniques and date from late 15th century to first half of 20th century. The investigated canvas paintings
required urgent restoration. Due to the fact that the restoration techniques and materials are greatly influenced
by the nature of the binders found in the painting layers, a number of 15 microsamples (around 1 mg) were
carefully collected. In order to identify the nature of the binders, these samples were then analyzed using
nuclear magnetic resonance (NMR), gas chromatography coupled with mass spectroscopy (GC-MS) and
Fourier transformed infrared spectroscopy (FT-IR). We aimed to confirm the presence of linseed oil in the
investigated artworks. To this end, we focused on the identification of saturated fatty acids biomarkers, as
these substances are not directly involved in the polymerization processes. The biomarkers were evidenced
as methyl esters by GC-MS, the most accessible analysis for their detection. The method presented herein
allows the analysis of the palmitic and stearic acids methyl esters, found in the old paintings microsamples.
It was thus possible to identify the presence of siccativated linseed oil in 13 out of the 15 investigated
samples. The results confirmed the proposed painting technique and allowed the correct choice of compatible
restoration materials and methods.
Keywords: canvas paintings, mixed oil-tempera techniques, restoration techniques, binders,
siccativated linseed
Paintings have a complex, layered structure containing
different inorganic and organic materials: support (wood,
canvas), pigments, binders and varnishes.
During time, paintings suffer different degradations due
to the action of environmental factors (light, temperature
and humidity), inadequate storage conditions and human
interventions. The preservation state of such artworks can
be gauged through their physico-chemical investigations.
The analysis of a painting (and in general of any artwork) is
primarily concerned with the identification of the
constituent materials. This knowledge is indispensable in
the scientific control of further restoration interventions.
These works can be performed only by respecting the
restoration principles - „Primum non nocere” and by using
identical or similar materials, compatible with the painting
technique employed by the artist.
The chemical characterization of organic substances
found in old paintings is of great importance in the
conservation of such artworks, as the organic components
of paintings are the most easily degraded. The identification
of organic compounds found in old paintings is challenging
due to both their complexity and to the changes inflicted
by the passage of time (aging, environmental influence,
external contamination), as well as to the non-homogeneity
of the structural layers. The identification is hindered by
the presence of inorganic compounds, the small sample
size and low quantity of such samples and by the
contamination risk inherited in the sampling and handling
of the painting samples [1]. Furthermore, the analyzed
samples must be representative for the investigated
paintings and they must be sampled without affecting the
integrity of the artworks.
In the area of cultural heritage, the GC-MS technique
can be successfully employed to identify and characterize
organic compounds and their degradation products [2].
This holds true especially when microsamples are involved,
as mass spectrometry is recognized as the best method to
identify organic materials, such as proteins, drying oils,
waxes, terpenic resins, and polysaccharide gums [3].
Furthermore, the analyses methods employed in the
present study (GC-MS, NMR and FT-IR) were also
successfully used for the characterization and identification
of binders [4, 5], both in qualitative and quantitative studies
[6].
The study of binders is of foremost importance in the
painting restoration process, as the binders define the
painting technique used. A binder is a compound having
the ability of joining together different materials and acting
as a dispersion medium for the pigments found in colored
layers. Successive painting layers do not usually contain
the same binder, making them hard to separate, extremely
thin and irregular.
In the complex structure of a painting binders usually
play a large role, leading to different painting techniques:
oil painting, tempera, watercolor, gouache, mixed
techniques etc. The study of binders thus helps to shed
light on the artist technique and even to identify the artistic
* email: polixenia.popescu@gmail.com Tel. +40 748 854082
REV. CHIM. (Bucharest) ♦ 63 ♦ No. 4 ♦ 2012
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Tabel 1
LINSEED OIL COMPOSITION
period or movement of the painting while playing an
important role in the restoration process.
Starting with the second half of 15th century, vegetable
oil has started to be used as binder in canvas painting. The
most common oil was linseed oil, due to its siccative
properties. Upon mixing with pigments, the oil forms
suspensions or emulsions, more durable the finer the
dispersion. In time, the oil layer darkens, thus making the
pigments have a darker tone. Light, atmospheric oxygen
and water transform the color layer into a thin, solid, elastic
and resistant film. Linseed oil has a complex composition
(table 1) [7] and its drying process has been thoroughly
studied due to its practical significance. It is unanimously
recognized that linseed oil drying takes places through an
oxidative radical mechanism, favored by light and
temperature conditions. The first step, of hydrogen
extraction form the bis-allyl methylene group of linoleic
acid, is favored by the conjugation stabilization of the
radical formed [8]. The same mechanism is involved in
the natural drying in time of oil found in older painting layers.
The situation where linseed oil is air oxidized at
temperatures of 150 – 300 oC is also common. Through
spectroscopic means it was possible to establish that by
increasing the drying temperature double bond oxidation
reactions, cis-trans isomerizations and Diels – Alder
reactions take place [9].
The formation of hydroxides and hydroperoxides was
additionally confirmed through mass spectroscopy. In the
oil oxidation process, free fatty acids are also formed.
These acids have a smaller chain than their parent acids
and are able to form soaps with some pigments [10]. The
degradation processes continue even after the oil layer is
dried and the polymer film is obtained [11]. The simplest
description of the polymer layer is that of a threedimensional structure encasing the esters of fatty acids.
The final step of the oil drying process is represented by
the polymerization of oleic acid. Only the palmitic and
stearic acids are not directly involved in the drying process
[12, 13].
Fatty acids can be identified through hydrolysis and
derivatization, followed by high pressure liquid chromatography coupled with fluorescence detection [13] or through
tetramethyl ammonium hydroxide pyrolysis and pyrolisisgas chromatography-mass spectrometry (Py-GC-MS)
technique [14], based also on the polymer film fatty acids
methylation reaction.
Although stearic acid is practically present in all
vegetable oils, in linseed oil palmitic acid is found in
quantities two or three times larger than stearic acid. For
this reason we have selected the methyl esters of palmitic
and stearic acids as GC-MS biomarkers. The mass spectra
of the aforementioned compounds are well known in the
literature. The most abundant cleavages in these
compounds are represented by α and β fragmentation of
the carboxylic ester group, followed by characteristic
fragmentation of the aliphatic chain, at m/z= 87, 143, 199.
In the present study, spectral analysis methods were
employed to identify the paint binder used in 15
microsamples taken from nine canvas paintings (table 2
for the list of collected samples). The paintings were
Table 2
LIST OF THE ANALYZED SAMPLES
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Table 2
continued
investigated and restored in the Brukenthal National
Museum, Sibiu laboratories. Seven paintings belong to the
Brukenthal Painting Galleries and two artworks belong to
other collections.
The Brukenthal Paintings Gallery was founded by Baron
Samuel von Brukenthal (1721-1803) and enriched since
then through donations and acquisitions. Today it consists
of an impressive number of artworks, grouped in several
collections: masterpieces (23 paintings), Dutch and
Flemish art (aprox. 450 paintings), Italian art, German and
Austrian art, modern and contemporary Romanian art. The
paintings investigated in this study belong to the European
and Romanian art collections.
Samples were collected from the nine investigated
paintings, all of which required urgent restoration
interventions. Eight artworks are painted in oil, on wood or
canvas. From these, the oldest date from the beginning of
17th century while the newest date from the first half of the
20th century. Twelve samples were carefully collected
during the initial investigations which preceded the
restoration work. Three more samples were collected from
the back side of the “Birth of Jesus” wood panel, from
“Proºtea Mare” polyptych altar. The wood painting was
done in the mixed oil-tempera technique and it dates from
the late 15th century. The samples were collected both
during the initial investigation (P 62) and during the
restoration works (P 139 and P 145), motivated in part by
the advanced decomposition of the paint layer of this
artwork.
Herein we discuss the confirmation of siccativated
linseed oil presence in the investigated microsamples, in
order to verify the painting technique used and to correctly
choose adequate restoration materials and methods,
compatible with the technique and binders.
In order to achieve the proposed goal, we have utilized
NMR, FT-IR and CG-MS spectrometric analyses to confer
valuable information on the presence of linseed oil in
painting layers. The reference materials, fresh and
siccativated linseed oil, were firstly characterized by NMR
and FT-IR. The experimental GC-MS method for the
REV. CHIM. (Bucharest) ♦ 63 ♦ No. 4 ♦ 2012
detection of siccativated linseed oil in microsamples was
then developed. After optimization, the methods were used
to investigate the samples. The analytical method for the
fatty acids detection from siccativated linseed oil, proposed
and verified in this paper, consists in sodium methoxide
methylation and analysis of the resulting isooctane extract
of palmitic and stearic methyl esters by GC-MS.
Experimental part
Materials and technique
The nuclear magnetic resonance spectra were recorded
at 298K on a Varian Gemini 300 apparatus at 300 MHz (1H)
and 75 MHz (13C) in deuterated chloroform using TMS as
internal standard. Infrared spectra were recorded on a
Bruker Tensor 21spectrophotometer using the ATR
(attenuated transmittance-reflectance) technique.
Gas chromatography was performed on a Trace GC Ultra
gas chromatograph fitted with an AS 2000 automatic
injector and a 10 μL Hamilton syringe, equipped with a TR
5 MS column of 30 m length, 0.25 mm diameter and 0.25
µm film thickness from Thermo. Detection was performed
on a Polaris Q ion trap mass spectrometer, all fitted modules
being provided by Thermo. Chromatographic data were
collected at an acquisition speed of three spectra/s. Data
was processed with the help of the Xcalibur software suite,
version 1.3 and for spectral identification was performed
by employing the NIST ‘02 library.
Methyl palmitate and methyl stearate were used as
purchased from Riedel, dry methanol was used as received
from Sigma-Aldrich, sodium and dry isooctane were used
as received from Merck. Helium was used as carrier gas.
Gravimetric measurements were performed on an AX 210
Mettler electronic balance. A Heidolph magnetic stirrer and
a Towson&Mercer ultrasonic bath were used during
laboratory work. Disposable syringe equipped with0.2 µm
cellulose filters were purchased from Schleicher&Schuell.
Procedure
Analysis strategy consists in few steps: 1. carefully
sampling, 2. methylation with sodium methoxide 3.
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369
extraction with isooctane, 4. filtration, 5. injection into gas
chromatograph-mass spectrometer. Sample preparation
consisted of mixing the microsample with 5 mL dry
methanol and 1 mL dry isooctane into a volumetric flask,
followed by the addition of 100 mg metallic sodium.
Constant stirring was applied until full sodium outlaying.
The samples were subject to sonication for 10 min, in order
to disintegrate the solids. As a result of the ensuing reaction,
the mixture heated and a part of isooctane evaporated.
The mixture was left to stand for 1 hour. The upper layer,
containing the dissolved isooctane methyl esters, was
separated by the methanol layer into a syringe, adjusted
with fresh isooctane to 0.5 mL and then subject to filtration
with disposable cellulose filter.
Chromatographic separation was performed at a 1 mL/
min helium carrier gas flow rate using the following
temperature program as: start at 100 oC, ramping up to
250o C at a 20 degrees/min rate and then isothermal regime
up to a final time of 12.5 min. Pressure increased from 81
psi at the analysis start up to 165 psi at the finish. Retention
times were 7.39 min for methyl palmitate and 8.53 min for
methyl stearate and compared against a reference solution
containing 0.1μg/mL of each ester. Injector port was heated
to 250oC and the injection volume was 5 μL with a split
flow of 10 mL/min. The high injection volume coupled with
low split flow assured a good sensibility and reliable
detection. Electron impact provided the ionization source,
at 70 eV. The scanning range was set at 50-350 atomic
mass units for 0.32 sec, at 300 V multiplier offset.
Results and discussions
The first step in this study was the recording of the
nuclear magnetic resonance spectra for commercially
available raw linseed oil. 1H-NMR (fig. 1) and 13C-NMR (fig.
2) spectra for raw linseed oil were presented as follow: 1HNMR(CDCl3, δ, ppm, J Hz): 5.37(m, H unsat); 4.30 (dd, 4.4,
11.8, 1H, CH2 -O), 4.15 (dd, 6.0, 11.8, 1H, CH2 -O), 2,81 (t,
6.0, CH2) ; 2.77 (dd, 4.4; 6.0, 1H); 2.31 (m, CH2); 1.60 (sl,
CH2); 0.98 (t, 7.4, CH3 terminal).
13
C-NMR(CDCl3 , δ, ppm): 173.33 (COO); 172.92 (COO);
132.05 (CH unsat ); 130.30 (CH); 130.11(CH); 129.81 (CH);
128.40 (CH unsat); 128.34 (CH unsat); 128.18 (CH unsat);
128.00 (CH unsat), 127.86 (CH unsat); 127.22 (CH unsat)
69.00 (CH-O); 62.21(CH 2O); 34.29 (CH 2), 34.13 (CH2),
32.01 (CH 2), 31.63 (CH 2 ); 29.87(CH 2); 29.81(CH 2);
29.70(CH 2); 29.70(CH 2 ); 29.43(CH 2 ); 29.28(CH 2);
29.22(CH 2); 27.32(CH 2 ); 25.73(CH 2 ); 25.64(CH 2);
24.94(CH 2); 22.79(CH 2 ); 22.68(CH 2 ); 22.60(CH 2);
14.38(CH2); 14.21(CH2).
The 1H-NMR spectrum of painting samples was recorded
and compared with that of reference siccativated linseed
oil, available from the Brukenthal Museum collections, in
order to identify the oil based binders. The 5.37 ppm NMR
multiplet signal (fig. 1) corresponds to the number of double
Fig. 1. 1H-NMR Spectrum for pure
linseed oil
Fig. 2.
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13
C-NMR Spectra for pure
linseed oil
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Fig. 3. 1H-NMR Spectra for siccativated
linseed oil from painting sample P 78
(below) and comparison with
reference (above)
Fig. 4. 13C-NMR Spectra for siccativated
linseed oil from painting sample P 78
bonds present in raw linseed oil, which sharply decrease
during the polymerization process. Thus siccativated oil
presents only saturated C-H signals, and the
aforementioned multiplet signal almost disappears. In
figure 3, the comparison between the 1H-NMR spectra of P
78 sample and reference is presented. As it can be noticed,
the spectra are almost identical and correspond to
siccativated linseed oil. The 5.37 ppm multiplet, specific
to the hydrogen atoms of double carbon-carbon bonds is
not found. As it can be seen in figure 2, the 13C-NMR
spectrum of raw linseed oil contains specific signals of sp2
carbons between 127 and 132 ppm. After the
polymerization process these signals disappear, as it is also
the case for the P 78 sample (fig. 4). The NMR behaviour is
consistent with the presence of siccativated linseed oil in
sample P 78. This observation is further strengthen by the
APT sequence (attached proton test) (CH 2, C2↑)(CH,
CH3↓), presented in figure 4.
The infrared spectrum of the reference siccativated oil
sample is presented in figure 5A. All peaks are broad, due
to the polymeric nature of the sample. The P 78 spectrum
is almost identical to that of the reference, confirming that
this sample mostly consists of siccativated linseed oil and
thus belongs to a paint layer done in the oil technique.
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The extraction procedure for the methyl esters was
optimized by using reference samples consisting of
siccativated linseed oil. Successive smaller samples were
methylated, extracted with iso-octane and analyzed by GCMS. The obtained fatty acid composition is in agreement
with the linseed oil composition, as palmitic acid is always
more abundant than stearic acid. The easiest way to
highlight the presence of these two acids is by comparing
the 7.39 and 8.53 min retention time peaks. Similar
abundance and fragmentation pattern was noticed for the
investigated and reference samples. At lower
concentrations, higher differences in fragment abundance
appear; for example the base peak changes from 143 m/
z to 87 m/z. In the case of samples with normalized ion
content of about 103, interference caused by background
noise are also apparent: peaks at 73 and 181 m/z,
characteristic for silanes, can be seen. These ions are due
to column bleeding. In order to improve the quality of
spectra with low normalized ion content, background noise
subtraction was performed. The signal-to-noise ratio (S/
N) was automatically computed for 7.39 and 8.35 min
retention times.
The mass spectrometer detector offers poor repeatability
of the results, which is only made worse by the decrease
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371
Fig. 5. Infrared spectrum for
siccativated linseed oil reference
sample (A), and for the painting
sample P 78 (B)
Fig. 6. Detection of palmitic acid methyl ester in sample P 77. Figure 6 A reference solution chromatogram, figure 6 B the
methylpalmitate spectrum from retention time 7.39 min, figure 6 C the chromatogram of the sample P 77 and
figure 6 D the spectrum corresponding to the retention time 7.39 min in figure 6 C.
of analyte concentration. Therefore results differed greatly
in different injections. However, such variation is acceptable
at such low concentrations. For this reason we choose as
a measure of detection the software generated signal to
noise ratio (S/N). In the case of P 66, P 70, P 75, P 77, P 78,
P 79, P 83, P 84, P 85B and P 93 samples vegetable oil was
detected by gas chromatography analysis, confirming that
the oil based painting technique was used.
Both the palmitic and stearic acid methyl esters were
detected in the P 70, P 77 and P 78 samples. Very good S/
N values were obtained for the palmitic acid derivative in
the case of the P 78 (S/N=313) and P 77 (S/N=612)
samples; good values were obtained in the case of the P
70 sample (S/N=270). Concerning the stearic acid ester,
low values of signal/noise were obtained: S/N=165 for P
77, S/N=188 for P 78 and S/N=214 for P 70 samples,
indicating trace presence of this compound.
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No methyl stearate was identified for the P 66, P 75, P
79, P 83, P 84, P 84B, P 85B, P 93 and P 96 samples.
Furthermore, P 84B and P 96 samples did not contain the
palmitic ester derivative.
A good detection of palmitic methyl ester was observed
for the P 79, P 84, P85B and P 93 samples, with S/N=316,
217, 207, 256, respectively. S/N values of 281 and 162 were
obtained for the P 66 and P 75 samples, for the
aforementioned compound. A low S/N=83 value was
obtained in the case of P 83.
The hypothesis that the “Birth of Jesus” panel is painted
in the oil – tempera mixed technique was confirmed by
the results of gas chromatography coupled with mass
spectrometry analysis on the P 62, P 139, P 145 micro
samples. The presence of acid methyl palmitate and
methyl stearate in the analyzed samples confirms the
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Table 3
LIST OF ANALYSES RESULTS
Fig. 7. Detection of stearic acid methyl ester in sample P 78. Figure 7 A reference solution chromatogram,
figure 7 B the methylstearate spectrum from retention time 8.53 min, figure 7 C the chromatogram of the sample
P 78 and figure 7 D the spectrum corresponding to the retention time 8.53 min in figure 2 C.
presence of vegetable oil and thus of the mixed painting
technique used to create the artwork. Both esters were
detected in the P 62 sample. The S/N value for the palmitic
derivative was 374 and for the stearic derivative a value of
233 was obtained. Negative results for methyl stearate
were obtained for the P 139 and P 145 samples. However,
the P 137 and P 145 samples showed the presence of
methyl stearate.
In the case of P 78, 1H-NMR analysis has confirmed the
presence of siccativated linseed oil, as it can be seen from
figure 3. Practically no double bond signals, present in raw
oil, can be noticed. In the case of FT-IR spectroscopy, the
broad 3400 cm-1 peak, corresponding to the presence of
OH groups can be noticed. The broad 800 – 1450 cm-1
peak was attributed to C-O-C and C-O bonds from esters
and hydroxides and the broad character can be explained
by the polymeric nature of the siccativated oil. The 1707
cm-1 peak, presenting a 1750 cm-1 shoulder corresponds to
carbonyl groups. The oxidation process may lead in time
to the formation of carbonyl groups, from hydroperoxides
fragmentations.
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The reference solution chromatogram is presented in
figure 6 A and that of sample P 77 in figure 6 C. The peaks
of interest, corresponding to palmitic acid methyl ester and
stearic acid methyl ester were found at retention times of
7.39 min and 8.53 min, respectively. Figure 6 B presents
the recorded spectrum at retention time 7.39 min from
reference solution containing methyl palmitate while
figure 6 D shows the similar spectrum of sample P 77. The
normalized level (NL) for the chromatograms had a value
of about 106 counts, which was large enough for a good
definition of chromatographic peaks (S/N > 10). Despite
the variation in the mass spectra, the retention times for
the compounds showed almost no variation. This fact gave
us confidence to assign the 7.39 min peak as methyl
palmitate for the P 77 sample. Lastly, the good value of this
result can be attributed to the presence of at least 10 data
points in the chromatogram peak, reinforcing the fact that
the experimental setup was correctly chosen. Negative
results were obtained in some cases (table 3).
Reference solution chromatogram is presented in figure
7 A and that of sample P 78 in figure 7 C. Figure 7 B shows
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373
the reference spectrum at retention time of 8.53 min
assigned as methyl stearate. A comparison with P 78 can
be seen in figure 7 D. The absolute abundance level of
base peak at m/z = 87 in the methyl stearate spectrum of
the reference solution was around ten times higher than
that of the sample. Despite of this fact, a good agreement
between ions and their abundance can be noticed. For this
reason, the 8.53 peak of P 78 could be assigned as methyl
stearate.
For each painting, the binder characterizes the paint
technique and the choice of restoration methods and
materials. In the case of oil paintings, the oil binder
polymerization leads in time to the formation of a resistant
layer. This layer allows wet cleaning with suitable solvents,
without risking the removal of color layers (as it is the case
for tempera paintings). Usually paintings have been
varnished several times. The varnish layer is thinned by
cleaning, but not entirely removed. The luminosity and
transparency depreciated, the first layer is thus removed.
The pigment layers are well fixed underneath the varnish
layer in paintings made with oil based binders. In the case
of tempera technique paintings, traditionally, restoration is
performed with egg emulsions, as the binders present are
egg – based. The binders lose their cohesion in time; the
emulsion acts to restore the color layer cohesion,
regenerating the binder layer in which pigments are
dispersed.
During the restoration work performed on the “Birth of
Jesus” polyptych altar panel from “Proºtea Mare” it was
observed that egg emulsion restoration could only be
successfully applied on some areas. This was true for both
the front and the back side of the artwork. Furthermore,
the macroscopic aspect of the color layer, as observed
after the varnish removal, suggested that the painting was
not done in the classical tempera technique. These facts
lead to the hypothesis that the panel was painted in the oil
– tempera mixed technique. This hypothesis is supported
by known historical data, as during the period in which the
work was created (late 15th century), the oil – tempera
mixed techniques was used experimentally in Europe.
During this time frame, the change from tempera to oil
painting took place. This corresponds to a change from
gothic style to renaissance style in European painting.
Conclusions
The analysis results confirm that siccativated linseed
oil is present in 13 out of 15 of the investigated samples.
This certifies that the artworks were painted using the oil
technique. Due to the fact that the painting technique is of
foremost importance in choosing adequate restoration
methods, these analyses had a great contribution to the
performed restoration works. In the particular case of the
“Birth of Jesus” panel, painted in the mixed oil – tempera
technique, the results were used not only in the restoration
and preservation processes, but also for the artwork
authentication in correlation with historical data.
The spectral analyses results presented herein will make
the object of a database which will be used for the
determination of painting techniques and, accordingly, for
paintings authentication, as well as in further restoration
and preservation activities of canvas paintings belonging
to the Brukenthal Paintings Gallery.
The quality of detection, as given by the S/N values, is
directly related to the investigated sample quantity for the
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samples P 66, P 70, P 75, P 77, P 78, P 79, P 83, P 84, P 85B
and P 93. In the case of P 78 sample, which had the highest
mass (1600 μg), S/N had great value for methyl palmitate.
For two samples (P 84B, P 96) positive detection was not
possible. The detection of palmitic acid methyl ester in the
investigated painting samples confirms the presence of
linseed oil, in high quantity. This means that the linseed oil
was employed as binder, certifying that the oil painting
technique was used.
For the samples P 62, P 139, P 145, GC-MS results are
not influenced by the sample mass, compound
identification is correlated with the oil quantity present in
the samples. The results confirm the presence of
siccativated linseed oil in these samples, certifying the
usage of the mixed oil – tempera technique for the painting
of “Birth of Jesus” panel.
Furthermore, the present study verifies that the proposed
method of investigation has proven to be suitable for the
goal of this paper.
Taking into account that the samples sizes were critical
small, around one milligram, the proposed method was
found to be quick, confident and reliable. The gas
chromatography method was successfully used to certify
the presence of linseed oil in old paintings and could be
routinely applied in further studies. Nuclear magnetic
resonance and Fourier transform infrared spectroscopy
were also successfully applied despite not being as
sensitive as gas chromatography-mass spectrometry.
Acknowledgement: Polixenia Georgeta Popescu thanks for the financial
support offered by the University „Politehnica” of Bucharest - POSDRU
ID 7713.
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Manuscript received: 12.12.2011
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