The key to successfully preserving any delicate material, whether it be an archaeological object, cultural heritage, or art, is knowing your material. Stakeholders and institutions responsible for overseeing appropriate conservation methods for paintings need to know which pigments, varnishes and canvas have been used to determine the suitable atmospheric conditions including lighting to keep the painting in, and to inform which chemicals can be safely used for cleaning. A commonly used method for identifying the composition of such materials is X-ray fluorescence (XRF), widely employed to characterize the elemental composition of painted heritage items (as well as other objects) and gaining in popularity (see Figures 1 and 2 from Harth, 2024). Its non-destructive, sensitive, and efficient nature makes it particularly suited at identifying the composition of various painting materials, notably pigments.
This shift towards using XRF techniques in painting analysis can be partly attributed to the debut of the M6 Jetstream in 2013, a commercial micro x-ray fluorescence (µXRF) scanning tool developed by Bruker. Unlike traditional analytical methods that heavily rely on spectra and graphs, this non-destructive X-ray fluorescence scanner produces elemental distribution images across entire painted surfaces. The development of XRF technology has allowed non-scientifically trained curators, researchers, and managers to gain a thorough understanding of the elemental data collected (see Figure 3 from Haddad et al, 2024).
The use case to generate element distribution maps or images of a continuous painted surface were published (Haddad et al 2024), presenting analysis of French painter Séraphine Louis’ paintings. This study used a combination of three complementary analysis methods – µXRF (M6 Jetstream) Raman Spectroscopy, and FTIR, to analyze six individual paintings to identify for each which pigments were used and the varnish composition.
Using this multi-spectral approach, Haddad et al, successfully identified several key pigments of interest in the painting with XRF, including lead white, zinc white, carbon black, red and brown ochres, umber, vermilion, alizarin lake, rhodamine B lake, Prussian blue, cobalt blue, ultramarine blue, chrome green, emerald green, viridian, cadmium yellow, and lead chromates (chrome yellow deep and light, zinc yellow, and chrome orange). Correctly identifying pigments is extremely valuable for the long-term preservation of these artworks. All pigments are at risk of being compromised due to light degradation, however, some pigments are particularly light-sensitive and require specific lighting conditions. Light-sensitive pigments such as Rhodamine B Lake and Zinc Chromate Yellow were both found in Louis’ paintings, and require moderate lighting during display to avoid light degradation.
Assessments to determine which cleaning treatments are appropriate and non-destructive for a given artwork are critical to successful custodianship and maintenance of artefact integrity. Potential for adverse chemical action during cleaning artworks requires careful assessment to avoid unintended damage. Haddad identified Prussian Blue in many of Louis’ artworks, either independently or mixed with Chrome Yellow, highlighting their susceptibility to buffered or chelated water solvents commonly used in wet cleaning. Additionally, the presence of Zinc White also suggests the potential formation of Zinc Carboxylates, which could lead to structural deterioration of the composition over time (Haddad et al, 2024). Such knowledge is pivotal to good practice and successful art conservation, for current and future generations to appreciate and study.
Haddad, A. et al. (2024) Painting on the margins: investigating the pigments, media, and techniques of Séraphine Louis. Heritage science. [Online] 12 (1), 85–19.
Harth, A. (2024) X-ray fluorescence (XRF) on painted heritage objects: a review using topic modeling. Heritage science. [Online] 12 (1), 17–20.
Findings of an ongoing regional evaluation study over concealed Proterozoic lithologies known to host magmatic nickel sulphides with potential to host other base-metal, gold and rare earth elements (“REE”) systems within the Fraser Range, Western Australia.
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