Elsevier

Journal of Cultural Heritage

Volume 14, Issue 1, January–February 2013, Pages 31-37
Journal of Cultural Heritage

Original article
Protein identification and localization using mass spectrometry and staining tests in cross-sections of polychrome samples

https://doi.org/10.1016/j.culher.2012.03.004Get rights and content

Abstract

The identification and localization of the proteinaceous binders are essential issues in studies of painting materials and techniques, for further proposing valid restoration and conservation treatments of the painted or polychrome works of art. The challenge for analytical chemists and conservation scientists is the availability of methods able to simultaneously identify and map the presence of the binders in the multilayered structure of a sample and the possibility to use a very low amount of sample from the studied art object (considering also the criteria of minimum sampling). These methods should be fast, reproducible in different artefacts and in case of mixture of protein-based binders with other non-proteinaceous constituents (oils, resins, waxes, gums etc.) and also economical (both in terms of materials and time consume). In this context, the present paper proposes an innovative protocol of investigation using two complementary techniques – Matrix-Assisted Laser Desorption/Ionisation – Time of Flight Mass Spectrometry (MALDI-TOF MS) and staining tests (one visible and one fluorescent stain) assisted by Optical Microscopy (OM) on cross-section of samples – for the simultaneous identification and mapping of protein – and oil-based binders in paint materials. The novelty is based on the use of MALDI-TOF MS on cross-sections of paints together with a fluorescent stain for protein identification and mapping (mainly used in the area of proteomics) complementing the use of a traditional visible stain for oil-based material identification. The protocol was successfully applied on several samples taken from a Czech medieval polychrome sculpture, entitled “The Mourning of Jesus Christ” (16th century) belonging to the Moravian Gallery (Brno).

Section snippets

Research aims

The research results presented in this paper are part of a larger study of materials and techniques used in a Czech Medieval polychrome sculpture illustrating “The Mourning of Jesus Christ” (16th century), that underwent partial conservation treatments in the Restoration Department of the Moravian Gallery in Brno in 1999 and complex restoration (consolidation, cleaning, and removal of over-paints, woodcarving accessories, binders, retouching) with the support of the Ministry of Culture from the

Sampling

The sculpture (Fig. 1), owned by the Convent of Minorits in Brno (Czech Republic), is a complex work of figurative woodcarving (illustrating the theme of “The Mourning of Jesus Christ”, comprising 11 male and female characters standing around the laid body of Christ after the Descent from the Cross) shaped in high relief (97 cm × 136 cm × 29 cm), made of four massive lime wood blocks together with several supplements dating around the year 1520. In Fig. 1 the image of the entire sculpture is given and

Results and discussions

The cross-section observations under visible and fluorescent light display a different structure and complexity of the layered composites according the area of sampling (Fig. 3, Fig. 4): from one or two layers of paint (mostly in case of incarnations–samples M1, M2, M8, and M10) over the thick ground layer to five or six coloured layers (as the case of samples taken from garments – M4, M5, M6, M7, M11 – where probably over-painting was done in the past and had to be removed by restoration

Conclusions

The presented work proposes a novel simple, relatively fast and reliable protocol for identification and mapping of animal glue and egg binders in polychrome samples with complex stratigraphical structures by the combination of MALDI-TOF MS and staining tests (one visible stain and one fluorescent stain). Surprisingly, the sensitivity of MALDI-TOF MS increases in the tests done on cross-sections, where the achievable amount of proteins was predicted lower than in the tests on bigger quantities

Acknowledgements

This work has been supported by Fundação para a Ciência e a Tecnologia (FCT/MCTES) in Portugal through grant No. PEst-C/EQB/LA0006/2011 and grant No. PTDC/EAT-EAT/116700/2010; by EU funds, project Operational Program Prague–Competitiveness (OP PC) CZ.2.16/3.100/22197, Grant No. 000746 from the Czech Ministry of Culture 000746, Grant No. 6046137305 from the Czech Ministry of Education, and by Financial support from Specific University Research (MSMT No. 21/2011) in Prague.

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