Analysis of Cultural Heritage Objects

Contact: Dr Signe Vahur, signe.vahur@ut.ee

 

Dr Signe Vahur carefully sampling paint pieces from the St. Luke altarpiece at the St. Annen Museum in Lübeck (Hermen Rode, 15th c.). Photo: Art Museum of Estonia

The research related to the investigation of cultural heritage objects started in our group in 2003 and specializes in conservation science, analytical chemistry of cultural heritage materials and, more recently, archaeological objects. This research group is the only one in the Baltics dedicated to this kind of investigation.

Our research interests are the investigation and development of methodologies for the qualitative and quantitative analysis of cultural heritage objects and their materials (paints, coatings, dyed textiles, paper components, etc.) with different instrumental techniques (ATR-FT-IR, SEM-EDS, XRD, GC-MS, MALDI-, ESI- and APCI-FT-ICR-MS, etc.) and also chemometric methods (PLS, DA, PCA, etc.). The applicability of the developed methodologies is not limited to cultural heritage materials: they can also be exploited in materials science, forensics, pharmaceutics, etc.

 

List of publications

Anal. Chim. Acta 2023, 342107. Laser-based analytical techniques in cultural heritage science – Tutorial review

71st ASMS Conference (June 4 – 8, 2023, Houston, USA) poster MP 479 references: click here (PDF)

Veg. Hist. Archaeobot2023. Multi-proxy analysis of starchy plant consumption: a case study of pottery food crusts from a Late Iron Age settlement at Pada, northeast Estonia

Talanta 2023, 252, 123805. Non-invasive analysis of natural textile dyes using fluorescence excitation-emission matrices

J. Therm. Anal. Calorim. 2023, 148 (4), 1647-1655. Influence of the end-temperature on the oil shale fast pyrolysis process and its products

ChemistrySelect 20238 (29), e202300835. Solubility of Mono-Aminoacridines

PLoS Comput. Biol. 202319 (4), e1011009. Genome-scale metabolic modeling reveals metabolic trade-offs associated with lipid production in Rhodotorula toruloides (Open Access)

bioRxiv2023, 2023.05.10.540254. Improving xylose consumption in Rhodotorula toruloides through heterologous expression of xylose reductase and xylulokinase. Preprint

Archaeometry 2022, 64 (1), 227-244. Classification of archaeological adhesives from eastern Europe and Urals by ATR-FT-IR spectroscopy and chemometric analysis 

Read more

 

 

Qualitative and quantitative analysis of various materials with ATR-FT-IR and reflectance-FT-IR

An important advancement from our group is the investigation into the possibilities of analysis of materials related to cultural heritage and conservation science with ATR-FT-IR spectroscopy (ATR-FT-IR) using far-IR region and extended IR region of 4000-80 cm-1 (mid-IR and far-IR region). Over the years, ATR-FT-IR spectra of various materials (paints, pigments, binders, coatings, mortars, textiles, etc.) have been acquired during different analysis projects of historical, industrial and construction paints and coatings as well as BSc, MSc, and PhD theses. We have assembled these ATR-FT-IR spectra of different materials into a spectral library and created an online database freely available at https://spectra.chem.ut.ee/. This library currently contains over 150 IR spectra and has been described in the article published in the Anal. Bioanal. Chem, 2016.

PCA classification graph of different textile fiber classes. https://doi.org/10.1186/s40494-019-0337-z

In recent years we have expanded the possibilities of spectral data analysis using different classification approaches (discriminant analysis (DA), principal component analysis (PCA), random forest, etc.) and developed useful quantitative methods using partial least squares (PLS) for various materials. In particular, we have demonstrated the applicability of ATR-FT-IR with PLS data analysis for quantifying the components of paint binders and pigments and also fillers like chalk and kaolinite in the paper composition. Recently we published an article where we used the developed ATR-FT-IR-PLS method to quantify the contents of 7 main classes of minerals in different clays.  

An important research topic in our group is also the qualitative analysis of textile fibres with ATR-FT-IR and reflectance-FT-IR and the development of classification methods (using DA and random forest algorithm) based on these spectra. Possibilities of semi-quantitative analysis of mixed fibres (registered with ATR-FT-IR) using PCA has also been investigated.

 

Development of MALDI-, ESI-, and APCI-FT-ICR-MS measurement methodologies for the analysis of resinous materials, textile dyes and archaeological lipids

Another important section in method development is dedicated to applying direct mass spectrometric techniques for the analysis of cultural heritage and archaeological materials.

With MALDI-, ESI-, and APCI-FT-ICR-MS it is possible to analyse very small samples and determine the components of similar materials with high resolution (HR) and high mass accuracy. We have developed FT-ICR-MS measurement methodologies with different ion sources (MALDI, APCI, and ESI) for the analysis of different natural resins (such as dammar resin, shellac, colophony, sandarac, and mastic), textile dyes (currently natural red dyes), and lipids content of food residues in archaeological samples.

Study of monoaminoacridines as MALDI(−)-MS matrix materials. https://doi.org/10.1021/jasms.1c00037

The development of FT-ICR-MS methods includes the introduction of novel internal calibration standards for positive (phosphazenes) and negative (sulpho-compounds) ion modes that can be used with MALDI, ESI, and APCI sources. For the MALDI-FT-ICR-MS analyses, the ageing of the widely used 2,5-DHB matrix material in the positive mode has been investigated, and its suitability for the analysis of cultural heritage materials has been evaluated. Besides that, during our investigation, we introduced new matrix material candidates for the negative mode MALDI-MS (at first 3-aminoacridine and in recent research also other monoaminoacridines).

Currently, the work continues to extend and improve the measurement methodologies for the analysis of resinous materials, paint binders, and archaeological samples. For that, we are testing novel internal calibration compounds in positive and negative modes for the analysis with MALDI-, ESI-, and APCI-MS; direct (without dissolution) analysis of materials with MALDI-MS and novel matrix materials for positive and negative ion mode MALDI-MS. 

 

Investigation of textile dyes, paint binders, and resinous materials with GC-MS and HPLC-MS

In recent years we have expanded our research field to the analysis of textile dyes, paint binders, and resinous materials with chromatographic and mass-spectrometric techniques.

Identifying dyes in textiles is challenging: samples are very small, analyte concentrations are low, and their decomposition products complicate the interpretation. We have developed a multi-instrumental approach for the analysis of natural red textile dyes utilizing the following techniques: LC-DAD, LC-FLD, LC-ESI-QQQ-MS, also ESI-FT-ICR-MS and MALDI-FT-ICR-MS. During this work library of chromatograms and mass spectra, along with optical UV-Vis absorption and fluorescence spectra (altogether 113 chromatograms/spectra), was created. Work with this topic continues, and other dyes are under investigation.

Pigment concentration effect on the drying of linseed oil. https://doi.org/10.3390/molecules26082218

Investigation of paint binders is still challenging. In our group, we started binder analysis with oils by developing a method to determine their quantitative composition with GC-MS and GC-FID and performed a comprehensive quantitative comparison of four well-known derivatization methods (TMTFTH, NaOEt–BSTFA, KOH–BSTFA, and ACM derivatization). This is the first time such a wide-scale comparison has been undertaken in terms of absolute quantification. One developed quantitative GC-MS derivatization method was applied for the analysis of aged oil paint samples. The research continues with the investigation of the composition of other binders with GC-MS and py-GC-MS.

 

Collaboration

We have good collaborations with the following Estonian museums, conservation centers, and archives: Art Museum of Estonia, Estonian National Museum, Conservation and Digitization Centre Kanut, the National Archives of Estonia, etc. They have been helping us with know-how and providing real-life samples. We also have good collaborations with other units of the University of Tartu: Institute of History and Archaeology, Department of Geology, University of Tartu Library, University of Tartu Museum, etc. The Chair of Analytical Chemistry is the lead partner of the Estonian Centre of Analytical Chemistry (ECAC), thereby we have access to the majority of equipment in the country.

We have participated in over 70 different projects or contracts with 20 conservation organizations and museums from Estonia and abroad.

 

https://www.ackermann.ee/en/

Currently running comprehensive research projects:

  • Signe Vahur’s Personal Research Funding Team grant (PRG1198) “Development of laser-based pen-type probe-MS system for the analysis of cultural heritage objects (1.01.2021−31.12.2025)”.
  • PR04019, “Bernt Notke: The Research and Conservation of the Retable of the Church of the Holy Spirit (1.01.2019−31.12.2024)”, Hilkka Hiiop, Estonian Academy of Arts. 
  • Technical art history research project (2016–2022) „Christian Ackermann – Tallinn’s Phidias, arrogant and talented”. This is a grandiose collaboration research project with the Art Museum of Estonia and with the Estonian Academy of Arts. In this project, sixteen different cultural heritage objects (altars, pulpits, coat of arms, sculptures, etc) from the city and country churches located in various parts of Estonia will be investigated.

Past research projects we participated in:

  • Signe Vahur’s Personal Research Funding (PUT1521) “Quantitative instrumental analysis of historical painting materials (1.01.2017−31.12.2020)”.
  • Rode Altarpiece in Close-up project related to the history, material investigation, and conservation of the Retable of the High Altar of Tallinn’s St. Nicholas’ Church. This work is carried out in collaboration with the Art Museum of Estonia.
  • Colour scheme investigation of Medieval terracotta figurines from St. John’s Church in Tartu from 14th c. This work is carried out in collaboration with the Estonian Academy of Arts (Research and Development Agreement between UT and Estonian Academy of Arts).
  • Participation in the international research scheme Early Pottery Research Group (led by the University of York, UK).
  • Personal research grant Feast in afterlife: Multidisciplinary study of ritual food in conversion period cemetery at Kukruse, NE-Estonia.

Award by the Estonian Research Council for popularizing science