Painting materials and Microanalysis of Fine Arts

Contact person: D. Hradil, ALMA laboratory (http://www.alma-lab.cz/eng)

Laboratory ALMA is a joint workplace of the Institute and the Academy of Fine Arts in Prague.

Analysis of Artworks

In the laboratory we study historical as well as contemporary painting materials, processes of their preparation, natural localities of origin and also historical context of their use. We examine their technological properties and chemical interactions in colour layers. In materials themselves and in procedures of their preparation we are able to find specific signs characterizing different regions and periods. These characteristics are thus helpful in the tracing of the artwork provenance.

We are still searching new ways how to find out these materials signs of artworks in a manner friendlier to the painting. Particularly, it includes an application of portable analytical methods with no need of contact with the artwork and no need of sampling. Thus we can collect data more effectively and cheaper, directly at the location of the artwork (not only in relation to its restoration).

In the field of laboratory instrumental analysis of microsamples we pay attention to development of such procedures that minimize the risk of misleading interpretations, which is a common phenomenon in analyses carried out on a purely service basis. Thanks to close collaboration with restorers and art historians we know how to compare and integrate materials, technological and artistic signs within interdisciplinary discussion. Then we are able to relate the artwork with a certain historical period, to interpret its original colouring, or to propose the best possibilities of its further protection and evaluation. 

Legend to figure:

Clay minerals with layered structures represent a common component of traditional earthy pigments. They give very useful properties to the pigment, e.g. the adhesive force to different surfaces. They are also reactive and can be chemically modified. They react with organic binders in the colour layer and thus form organo-clay complexes. Thanks to their structural and chemical variability they also represent sensitive indicators of natural processes of their formation and therefore they can be used as one of indicators of the provenance of materials used by the artist. In our laboratory, we apply an unconventional method of X-ray powder microdiffraction to characterise different clay structures found in microsamples of colour layers. On the figure, there is an example of attribution of one anonymous painting to the Italian provenance based on the presence of characteristic mixed-layered clay structure. A microsample casted in a polyester resin (A), and polished in the cross-section (B) is subjected to non-destructive analysis and the resulting diffraction pattern is then compared with a ground of reference painting of known authorship.

Project Funding

This work is supported by research projects of both institutions that established the joint workplace, e.g. by the project of the Ministry of Culture of the Czech Republic DF12P01OVV048 (2012-2015) and Czech Science Foundation projects14-22984S (2014-2016) and 17-25687S (2017-2019).

Selected Papers

• Hradil D., Hradilová J., Bezdička P., Serendan C.: Late Gothic / Early Renaissance gilding technology and the traditional poliment material "Armenian bole": truly red clay, or rather bauxite? Applied Clay Science 135 (2017), 271-281.

• Košařová V., Hradil D., Hradilová J., Čermáková Z., Němec I., Schreiner M.: The efficiency of micro-Raman spectroscopy in the analysis of complicated mixtures in modern paints: Munch’s and Kupka’s paintings under study. Spectrochimica Acta – Part A: Molecular and Biomolecular Spectroscopy 156 (2016), 36-46.

• Hradil D., Bezdička P., Hradilová J., Vašutová V.: Microanalysis of clay-based pigments in paintings by XRD techniques. Microchemical Journal 125 (2016), 10-20.

• Švarcová S. Čermáková Z., Hradilová J., Bezdička P., Hradil D.: Non-destructive micro-analytical differentiation of copper pigments in paint layers of works of art using laboratory-based techniques. Spectrochimica Acta – Part A: Molecular and Biomolecular Spectroscopy 132 (2014), 514-525.

• Košařová V., Hradil D., Němec I., Bezdička P., Kanický V. Microanalysis of clay-based pigments in painted artworks by the means of Raman spectroscopy. Journal of Raman Spectroscopy 44 (2013), 1570-1577.

• Švarcová S., Kočí E., Bezdička P., Hradil D., Hradilová J.: Evaluation of laboratory powder X-ray micro-diffraction for applications in the field of cultural heritage and forensic science. Analytical and Bioanalytical Chemistry 398 (2010), 1061 – 1076.

Degradation processes in painted artworks

Since its creation, a painted artwork has been exhibited for viewer’s eyes as well as it has been exposed to action of a wide range of factors affecting its contemporary appearance at once. Degradation processes occurring in paintings result often in undesirable changes of their appearance caused by colour changes of original pigments or loss of cohesion of paint layers. Combining both, knowledge of historic painting materials and knowledge of their stability in a given environment, we are able to describe a manifestation of a damage and to identify its causes, furthermore we can reconstruct an original appearance and formulate some recommendation for restoring and conservation of an artwork.
The study of degradation processes in painted artworks is based on the detailed material investigation of a given artwork and on the knowledge of its environment. Besides knowledge of previous restoration/conservation interventions are also contributing. Secondary changes of materials result often from a synergic effect of various factors, such as climatic conditions (e.g. temperature and relative humidity fluctuations, intensity of UV radiation), action of aggressive agents (e.g. salt solutions raising through the masonry, metabolites of microorganisms), unsuitable combination of materials in paint layers (e.g. coincident reactions of pigments and binders), unsuitable choice of materials for a given environment (e.g. application of coper and/or lead-based pigments into wall paintings), or even inconvenient or expired restoration/conservation treatment (e.g. relining of new canvas on a painting containing temperature-sensitive pigments, inappropriate cleaning agents, aged synthetic resins used as consolidators of paint layers). Performing model experiments, we clarify mechanisms of degradation.  

Legend to figure:

Being rarely occurring in painted artworks, the blue pigment vivianite (Fe₃(PO₄)₂·8H₂O) can be considered as one of the characteristic materials features, so-called fingerprints. The most frequent use of vivianite is documented in historic regions of Germany and Austria, furthermore in the Flemish paintings of the 17th century; in the Czech region, it is typical for Jean Georg de Hamilton, a painter of the turn of the 17 and 18th century (A). However, identification of vivianite is often complicated because of degradation processes leading to both, the substantial change of colour and the change of crystal structure, including the change of chemical composition. Gradational oxidation of iron from the oxidation state II to the oxidation state III results in the change of crystal structure from monoclinic to triclinic one, compensating the change of the cation charge (and thus also its size). Progressing oxidation can finally result in a total collapse of crystal structure of original vivianite under formation of amorphous santabarbaraite (Fe₃(PO₄)₂(OH)₃·5H₂O), which is accompanied by colour change from originally blue over greyish green to the final yellow-brown (B). We found that this process is significantly accelerated in cases when vivianite is exposed to even short-time thermal action above 70°C, when aggressive oxidation of iron is taking place. This i tis obvious from the drift of the main diffraction line of vivianite (15,35 Å) to the position 15,2 Å corresponding to FeIII-rich metavivianite (C). Such temperatures are easily achievable for example by rentoalage, a restoration treatment in which a new canvas is relined on the reverse of an old one.

Project Funding

This work is supported by research projects of both institutions that established the joint workplace, e.g. by the project of the Ministry of Culture of the Czech Republic DF12P01OVV048 (2012-2015) and Czech Science Foundation project 17-15621S (2017-2019).

Selected Papers

• Čermáková Z., Švarcová S., Hradilová J., Bezdička P., Lančok A., Vašutová V.,  Blažek J., Hradil D.: Temperature-related degradation and colour changes of historic paintings containing vivianite. Spectrochimica Acta – Part A: Molecular and Biomolecular Spectroscopy 140 (2015), 101-110.

• Čermáková Z., Bezdička P., Němec I., Hradilová J., Šrein V., Blažek J., Hradil D.: Naturally irradiated fluorite as a historic violet pigment: Raman spectroscopic and X-ray diffraction study. Journal of Raman Spectroscopy 46 (2015), 236-243.

• Hradil D., Hradilová J., Bezdička P., Švarcová S., Čermáková Z., Košařová V., Němec I.: Crocoite PbCrO4 and mimetite Pb5(AsO4)3Cl: rare minerals in highly degraded Mediaeval murals in Northern Bohemia Journal of Raman Spectroscopy 45 (2014), 848-858.

• Hradil D., Hradilová J., Kočí E., Švarcová S., Bezdička P., Maříková-Kubková J.: Unique Pre-Romanesque murals in Kostoľany pod Tríbečom, Slovakia:  painting technique and causes of damage. Archaeometry 55/4 (2013), 691-706.

• Švarcová S., Hradil D., Hradilová J., Kočí E., Bezdička P.: Microanalytical evidence of origin and degradation of copper pigments found in Bohemian Gothic murals. Analytical and Bioanalytical Chemistry 395 (2009), 2037-2050.

• Kotulanová E., Bezdička P., Hradil D., Hradilová J., Švarcová S., Grygar T.: Degradation of lead-based pigments by salt solutions. Journal of Cultural Heritage 10 (2009), 367-378.