Publications of our work group at chair of Analytical Chemistry, University of Tartu, Estonia

The analytical chemistry research related to cultural heritage objects started in our group in 2003 and is specialised in conservation science, analytical chemistry of cultural heritage objects and more recently also archaeological objects.

We have good collaboration with different Estonian museums, conservation centres and archives, including other units of University of Tartu (Institute of History and Archaeology, Department of Geology, University of Tartu library). During the years (since 2003) we have published with our collaboration partners several scientific and popular scientific publications.

Here are list of our main publications. If you need more information please contact signe.vahur(at)




Identification and classification of textile fibres using ATR-FT-IR spectroscopy with chemometric methods.

AUTHORS: Pilleriin Peets, Ivo Leito, Jaan Pelt, Signe Vahur.
JOURNAL: Spectrochimica Acta Part A. 2017, 173, 175−181.
The possibility of classification of single- and two-component textile materials using ATR-FT-IR spectra and chemometric methods, principal component analysis (PCA) and discriminant analysis, was assessed. Altogether 89 textile samples belonging to 26 different types (11 one- and 15 two-component textiles) were investigated. It was found that PCA classification using only two or three principal components (PCs) enables identifying different one- and two-component textiles, although with two important limitations: it was not always possible to distinguish between the cellulose-based fibres (cotton, linen and in some cases viscose) and it was only partly possible to distinguish between silk and wool. The statistical discriminant analysis can use as many PCs as there are sample classes and due to that can discriminate between single-component fibres, including viscose from linen and cotton as well as silk from wool. Besides that, in both of these cases, involving optical microscopy as an additional technique enabled unequivocal identification of the fibres. The possibilities of semi-quantitative analysis of mixed fibres (cotton-polyester, wool-polyester and wool-polyamide) with PCA were investigated and it was found that approximate quantitative composition is obtainable if for the mixed fibre sample a number of spectra are averaged in order to minimize the effect of structural inhomogeneity. For approximate content determination 25 spectra of selected two-component samples were registered for calibration and the averaged spectrum for each sample was computed. Due to the structural inhomogeneity of mixed textiles, obtaining accurate quantitative composition from real samples is not possible with ATR-FT-IR. The main problems with ATR-FT-IR-PCA classification are (1) difficulties in getting high quality spectra from some textiles (e.g. polyacrylic), (2) inhomogeneity of the textile fibres in the case of two-component fibres and (3) intrinsic similarity between the spectra of some fibres (e.g. cotton and linen). In order to test the homogeneity of mixed fibres, microscopic and IR-microspectroscopic analysis was carried out.

Multi-method analysis of avian eggs as grave goods: revealing symbolism in Conversion period burials at Kukruse, NE Estonia.

AUTHORS: Tõnno Jonuks, Ester Oras, Julia Best, Beatrice Demarchi, Raivo Mänd, Samantha Presslee, Signe Vahur.
JOURNAL: Environmental Archaeology: The Journal of Human Palaeoecology. 2017, xx−xx (in press)


Alkali activated construction materials: Assessing the alternative use for oil shale processing solid wastes.

AUTHORS: Päärn Paiste, Martin Liira, Ivo Heinmaa, Signe Vahur, Kalle Kirsimäe.
JOURNAL: Construction and Building Materials. 2016, 122, 458− 464.


The potential of oil shale ash wastes as a source material for geopolymeric or alkali activated construction materials was assessed using structural, XRD, SEM, SEM-EDX, ATR-FTIR and 29Si MAS-NMR methods. Fresh, unhydrated furnace bottom and cyclone separator ash along ash plateau sediment were used in combination with 5 M NaOH and Na2SiO3 solutions with SiO2/Na2O ratios of 2.72 and 1.5 as alkaline activators, under ambient curing conditions. Our analytical results show that only activator solutions containing soluble silicate will induce the formation of amorphous C-(A)-S-H gel, giving the samples 8 times higher compressive strength (8.5 MPa) than samples exhibiting cementitious properties upon hydration (1.25 MPa).

ATR-FT-IR spectral collection of conservation materials in the extended region of 4000-80 cm–1.

AUTHORS: Signe Vahur, Anu Teearu, Pilleriin Peets, Lauri Joosu, Ivo Leito.
JOURNAL: Analytical and Bioanalytical Chemistry. 2016, 408 (13), 3373−3379.


In this paper, a spectral collection of over 150 ATR-FT-IR spectra of materials related to cultural heritage and conservation science has been presented that have been measured in the extended region of 4000-80 cm–1 (mid-IR and far-IR region). The applicability of the spectra and, in particular, the extended spectral range, for investigation of art-related materials is demonstrated on a case study. This collection of ATRFT-IR reference spectra is freely available online ( and is meant to be a useful tool for researchers in the field of conservation and materials science.

Diagenetic fate of bioapatite in linguliform brachiopods: multiple apatite phases in shells of Cambrian lingulate brachiopod Ungula ingrica (Eichwald).

AUTHORS: Liisa Lang, Kalle Kirsimäe, Signe Vahur.
JOURNAL: Lethaia. 2016, 49 (1), 13-27.
Fossil skeletal apatites vary in their composition and can yield mixed biochemical, environmental and diagenetic information. Thus, it is important to evaluate the diagenesis spatially inside the skeleton. We study the cross sections of shells of the Furongian lingulate brachiopod Ungula ingrica from Estonia using the Attenuated Total Reflectance – Fourier Transform Infrared (ATR-FTIR) microspectroscopic and energy dispersive spectroscopic (EDS) mapping and show for the first time that different structural laminae of the shell have different chemical compositions. Compact laminae are rich in PO43−, Na, Mg and poor in F and Ca. Porous (baculate) laminae are rich in carbonate anions, Ca and F, but contain less Na and Mg. The ATR-FTIR spectra show further differences in the ν2 carbonate region, where the IR band at 872 cm−1 in compact laminae is replaced by a strong band at 864 cm−1 in baculate laminae. The changes in shell apatite suggest different origins of the apatite phases. Compact laminae are likely chemically less altered and could potentially carry more reliable palaeoenvironmental or geochemical information than the apatite in baculate laminae, which is mostly authigenic in its origin.


2,5-Dihydroxybenzoic acid solution in MALDI-MS: ageing and use for mass calibration.

AUTHORS: Anu Teearu, Signe Vahur, Uko Haljasorg, Ivo Leito, Tõiv Haljasorg, Lauri Toom.
JOURNAL: Journal of Mass Spectrometry. 2014, 49, 970-979.


2,5-Dihydroxybenzoic acid (DHB) is one of the most widely used and studied matrix compounds in matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. However, the influence of ageing of the DHB solution on the MALDI mass spectra has not been yet systematically studied. In this work, the possible changes occurring in the acidified acetonitrile/water solution of the MALDI matrix compound DHB during 1-year usage period have been monitored with MALDI-Fourier transform ion cyclotron resonance mass spectrometer (MALDI-FT-ICR-MS) and attenuated total reflectance Fourier transform infrared (ATR-FT-IR) spectroscopy. No significant ageing products have been detected. The ability of the aged DHB solution to act as a MALDI matrix was tested with two materials widely used in art and conservation – bone glue (a proteinaceous material) and shellac resin (a resinous material) – and good results were obtained. A number of peaks in the mass spectra measured from the DHB solution were identified, which can be used for internal calibration of the mass axis.

ATR-FTIR spectroscopy and quantitative multivariate analysis of paints and coating materials.

AUTHORS: Philippa Alice Hayes, Signe Vahur, Ivo Leito.
JOURNAL: Spectrochimica Acta Part A. 2014, 133, 207-213.


The applicability of ATR-FTIR spectroscopy with partial least squares (PLS) data analysis was evaluated for quantifying the components of mixtures of paint binding media and pigments, and alkyd resins. PLS methods were created using a number of standard mixtures. Validation and measurement uncertainty estimation was carried out. Binary, ternary and quaternary mixtures of several common binding media and pigments were quantified, with standard measurement uncertainties in most cases below 3 g/100 g. Classes of components – aromatic anhydrides and alcohols – used in alkyd resin synthesis were also successfully quantified, with standard uncertainties in the range of 2–3 g/100 g. This is a more demanding application because in alkyd resins aromatic anhydrides and alcohols have reacted to form a polyester, and are not present in their original forms. Once a PLS method has been calibrated, analysis time and cost are significantly reduced from typical quantitative methods such as GC/MS. This is beneficial in the case of routine analysis where the components are known.

Analysis of dammar resin with MALDI-FT-ICR-MS and APCI-FT-ICR-MS.

AUTHORS: Signe Vahur, Anu Teearu, Tõiv Haljasorg, Piia Burk, Ivo Leito, Ivari Kaljurand.
JOURNAL: Journal of Mass Spectrometry. 2012, 47(3), 392 – 409.


Comprehensive analysis of high-resolution mass spectra of aged natural dammar resin obtained with Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR-MS) using matrix-assisted laser desorption/ionization (MALDI) and atmospheric pressure chemical ionization (APCI) is presented. Dammar resin is one of the most important components of painting varnishes. Dammar resin is a terpenoid resin (dominated by triterpenoids) with intrinsically very complex composition. This complexity further increases with aging.
Ten different solvents and two-component solvent mixtures were tested for sample preparation. The most suitable solvent mixtures for the MALDI-FT-ICR-MS analysis were dichloromethane-acetone and dichloromethane-ethanol. The obtained MALDI-FTMS mass spectrum contains nine clusters of peaks in the m/z range of 420–2200, and the obtained APCI-FTMS mass spectrum contains three clusters of peaks in the m/z range of 380–910. The peaks in the clusters correspond to the oxygenated derivatives of terpenoids differing by the number of C15H24 units. The clusters, in turn, are composed of subclusters differing by the number of oxygen atoms in the molecules.
Thorough analysis and identification of the components (or groups of components) by their accurate m/z ratios was carried out, and molecular formulas (elemental compositions) of all major peaks in the MALDI-FTMS and APCI-FTMS spectra were identified (and groups of possible isomeric compounds were proposed). In the MALDI-FTMS and APCI-FTMS mass spectrum, besides the oxidized C30, triterpenoids also peaks corresponding to C29 and C31 derivatives of triterpenoids (demethylated and methylated, correspondingly) were detected.
MALDI and APCI are complementary ionization sources for the analysis of natural dammar resin. In the MALDI source, preferably polar (extensively oxidized) components of the resin are ionized (mostly as Na+ adducts), whereas in the APCI source, preferably nonpolar (hydrocarbon and slightly oxidized) compounds are ionized (by protonation). Either of the two ionization methods, when used alone, gives an incomplete picture of the dammar resin composition.


Investigation of the adhesive residue on the flint insert and the adhesive lump found from the Pulli Early Mesolithic settlement site (Estonia) by micro-ATR-FT-IR spectroscopy.

AUTHORS: Signe Vahur, Aivar Kriiska, Ivo Leito.
JOURNAL: Estonian Journal of Archaeology. 2011, 15 (1), 3-17.


The chemical composition of the flint insert and the black adhesive layer on it and of the adhesive lump found from the Early Mesolithic Pulli settlement site was determined by the attenuated total reflectance Fourier transform infrared(ATR-FT-IR)spectroscopy. The black adhesive lump and layer on the artefact is birch bark tar probably mixed with some fat and possibly containing some coniferous tree resin.

Studies of arhaeological bone structure by different analytical methods.

AUTHORS: Rudovica, V.; Viksna, A.; Katkevich, J.; Zarina, G.; Bitenieks, J.; Zicans, J.; Leito, I.; Vahur, S.
JOURNAL: Latvian Journal of Chemistry. 2011, No 3/4, 256 – 265.


Preservation of the structure of archaeological bones was studied by examining their physicochemical properties. The mechanical properties, and conductivity porosity, crystallinity and content of organic material were evaluated. These parameters were established to be suitable for characterizing changes in the course of time of archaeological bone structure. The obtained results revealed that the elastic modulus and conductivity changes depended on the porosity of bones; and the increase in crystallinity was correlated with a loss of organic matter.

ATR-FT-IR spectroscopy in the region of 550-230 cm-1 for identification of inorganic pigments.

AUTHORS: Signe Vahur, Anu Teearu, Ivo Leito.
JOURNAL: Spectrochimica Acta Part A. 2010, 75, 1061 – 1072.
A comprehensive study of ATR-FT-IR spectra of 40 inorganic pigments of different colours widely used in historical paintings has been carried out in the low wave number spectral range (550–230 cm−1). The infrared spectra were recorded from mixtures of pigment and linseed oil. It is demonstrated that this spectral range – essentially devoid of absorption peaks of the common binder materials – can be well used for identification of inorganic pigments in paint samples thereby markedly extending the possibilities of pigment identification/confirmation by ATR-IR spectroscopy into the realm of pigments having no absorptions in the mid-IR region. In some cases the method can be used alone for pigment identification and in many cases it provides useful additional evidence for pigment identification using other instrumental techniques (electron microprobe analysis, XRF, optical microscopy). Together with earlier work this study provides a comprehensive overview of the pigment identification possibilities using ATR-FT-IR as well as a collection of reference spectra and is expected to be a useful reference for conservation practitioners.


ATR-FT-IR spectroscopy in the region of 500–230 cm−1 for identification of inorganic red pigments.

AUTHORS: Signe Vahur, Ulla Knuutinen, Ivo Leito.
JOURNAL: Spectrochimica Acta Part A. 2009, 73, 764 – 771.


It is demonstrated that micro-ATR-FT-IR in the low wave number range (500–230 cm−1) can be well used for identification of pigments in paint samples thereby markedly extending the possibilities of pigment identification by ATR-IR spectroscopy into the realm of pigments having no absorptions in the mid-IR region. Reference spectra of pigments can be conveniently obtained by mixing them with linseed oil in approximately 1:1 mass ratio. Vermilion (or cinnabar), read lead, different red iron oxide pigments and cadmium red can be identified. In some cases the method can be used alone for pigment identification and in many cases it provides useful additional evidence for pigment identification using other instrumental techniques (electron microprobe analysis, XRF, optical microscopy).

Paint investigations of altar and pulpit in the church of St Mary, Vigala, Estonia.

AUTHORS: Signe Vahur, Kriste Sibul, Pia Ehasalu, Väino Sammelselg, Ivo Leito.
JOURNAL: e-Preservation Science. 2009, 6, 43-52. (online journal)


After an illegal over-painting of the seventeenth-century altar and pulpit in Vigala St. Mary’s church in Estonia, comprehensive paint layer investigations and chemical analysis studies – using optical microscopy, scanning electron microscopy – energy dispersive X-ray spectrometry (SEMEDS) and micro attenuated total reflectance Fourier transform infrared (micro-ATR FT-IR) spectroscopy – were carried out. The history of the colour scheme and paint compositions of the altar and the pulpit could be revealed to great extent. This is the first study of this kind in Estonia and it is expected to provide reference material for similar investigations in the Baltic and Northern-European region.

Estimation of uncertainty in electron probe microanalysis: iron determination in manuscripts, a case study

AUTHORS: Kristina Virro, Enn Mellikov, Olga Volobujeva, Väino Sammelselg, Jelena Asari, Lilli Paama, Jaana Jürgens, Ivo Leito
JOURNAL: Microchimica Acta, 2008, 162, 313-323.
A case study of ISO GUM-based estimation of measurement uncertainty of quantitative surface elemental analysis is presented. The analytical task was the measurement of iron content in the ink writing on the surface of an 18th century manuscript by electron probe microanalysis using a scanning electron microscope equipped with an energy-dispersive X-ray spectrometer (SEM/EDS). The problems that arise in uncertainty estimation of quantitative surface analysis are outlined (defining the measurand, preparing calibration standards, non-uniformity of the surface, etc) and ways of overcoming them are suggested. The average iron content on the ink-covered surface of the sample manuscript was found to be 0.12 ± 0.04 µg mm−2 (at confidence level 95.5%). Paper sheets with ink lines of known iron contents were used as calibration standards. The main source of uncertainty was the variability of the parallel measurement results from different locations of the sample surface (mostly due to the variations in the surface structure of paper), which contributed 78% of the total uncertainty. It is concluded that EPMA using a SEM/EDS is suitable for at least semi-quantitative determination of iron in the writing of ink-written manuscripts. Several specific issues in uncertainty analysis are pointed out that need further investigation.


Web-based Infrared Spectral Databases Relevant to Conservation.

AUTHORS: Signe Vahur, Kristina Virro, Ivo Leito.
JOURNAL: J. CAC, 2005, 30, 10-17.
Infrared spectroscopy is one of the most useful analytical methods available to art conservators today. This cost-effective method can be used to identify most organic as well as some inorganic compounds (most binders, fillers, and also some pigments); however, it is impossible to do this without reference spectra. Besides the commercial infrared (IR) spectral databases, there are numerous free infrared spectroscopy resources on the World Wide Web. This paper discusses several of such very good, and freely accessible, IR spectroscopy resources that cover most of the needs of conservators; some of the best-known commercial IR spectral databases are also reviewed. The focus of this paper is mostly on the spectra of traditional materials (mostly pre-20th century artists’ materials). The paper also discusses a number of recent articles that are related to material studies and present various useful spectra for conservation purposes. Many of the sites discussed will be known to experienced infrared spectroscopists, but it is hoped that this paper will be a useful review of reference resources for museum professionals new to the field of infrared spectroscopy.




Investigation of varnishes with different analytical methods.

AUTHORS: Anu Teearu, Signe Vahur, Ivo Leito.
JOURNAL: Renovatum Anno, 2015. (online issue)

Infrared Spectroscopy in Investigation of Textile Fibres.

AUTHORS: Pilleriin Peets, Signe Vahur, Ivo Leito.
JOURNAL: Renovatum Anno. 2015. (online issue)


Establishing a Conservation and Research Project for the Holy Spirit Altarpiece by Bernt Notke.

AUTHORS: Pia Ehasalu, Signe Vahur.
BOOK: Art, Cult and Patronage. Die visuelle Kultur im Ostseeraum zur Zeit Bernt Notkes. Anu Mänd, Uwe Albrecht (Eds.). Ludwig, 2013, 216 – 227.


Crucifix of Kolga-Jaani, research and interpretations.

AUTHORS: Krista Andreson, Pia Ehasalu,  Signe Vahur.
JOURNAL: Renovatum Anno. 2012, 21 – 33.
The article focuses on the research results of a really rare 14th-century wooden sculpture that comes from a village church in Estonia. The interpretation of the research results, the attribution and options of further conservation are discussed. Various investigations on technology and materials were implemented. CT scanning was necessary to ascertain the construction and pinpoint the damages and later-day attachments, crosscut samples verified the layers of paint and helped to determine the persistency of polychrome and to clarify what kind of pigments, binding- and filling substances should be used and tested for further conservation.


Georg Johann von Wrangell’s coat of arms-epitaph from Luganuse Church.

AUTHORS: Signe Vahur, Maria Lillepruun, Pia Ehasalu
JOURNAL: Renovatum Anno. 2010, 59 – 63.
The coat of arms-epitaph of Georg Johann von Wrangell, made in the middle of the 18th century, supposedly by Anthony Rabe, was brought to the Conservation Centre Kanut from the Lüganuse Church, at the end of 2008. The arms-epitaph, decorated with late Baroque and Rococo elements was totally covered with lime paint, severely stained, with the layers of paint flaking from the timber surface. The initial colour schema of the arms was visually not to be seen. One of the main aims of the conservation works was to remove the lime paint, but not by deteriorating the paint layers underneath. In order to determine the paint layers, microscopic studies were conducted during the conservation process. After more than a year-long complicated and extensive conservation, the arms-epitaph regained at least a part of its quondam majesty and was installed on the wall of the Lüganuse Church choir-room at the end of 2009, to be admired by public.


Restoration and installation of the altar of St. Paul’s Church in Hanila.

AUTHOR: Signe Vahur
JOURNAL: Renovatum Anno. 2010, 78 – 83.
The Baroque style altar of St. Paul’s Church in Hanila was made by wood-carver Dietrich Walter at the beginning of the 18th century. The altar stayed in the Hanila Church up until 1975, and was partially handed over to the Estonian Art Museum after the congregation stopped its operation. During the next thirty-two years, the altar details have been preserved in different museum repositories. Such movement of altar details between different locations, and versatile micro-climatic conditions resulted in the flaking of the paint layer and gilding from the surface, and also constructional and mechanical damage. The restoration of altar details commenced in the Conservation Centre Kanut in 2007, lasting for approximately two years, due to the voluminous and time-consuming nature of the work. One of the more extensive and complicated stages was the assembly of the altar details and the installation thereof on its initial location in the Hanila Church in spring 2009.


Ebbe Ludwig von Toll’s coat of arms-epitaph in Kaarma Church.

AUTHORS: Maria Lillepruun, Signe Vahur, Pia Ehasalu, Maike Naumann.
JOURNAL: Renovatum Anno. 2010, 54 – 58.
The coat of arms-epitaph, from the Kaarma Church on Saaremaa island, belonging to the chief lieutenant of the Swedish army, Ebbe Ludwig von Toll, was made in 1693, probably in Christian Ackermann’s workshop. The arms-epitaph, at the time in an extremely poor condition, was brought into the Conservation Centre Kanut in spring 2007, split into several details. All the details were very soiled, the remaining paint layers partially flaking from the base, with some details and the entire text board being covered with Japanese paper to prevent paint layer from dropping. The condition of the object was assessed prior to conservation, with additional technological studies. In the course of a complicated conservation process, it was possible to restore the constructional integrity of the arms-epitaph, and in 2008 the item was returned to the Kaarma Church for display.


Hidden and found. Two small coat-of-arms from St. Michael’s church in Jõhvi.

AUTHORS: Pia Ehasalu, Ingrid Pihelgas, Signe Vahur, Enn Tedre.
JOURNAL: Renovatum Anno. 2006, 37 – 40.


Study of chemical composition of paintings based on FT-IR spectroscopy method.

AUTHOR: Signe Vahur
JOURNAL: Renovatum Anno. 2004, 53 – 58.