2 July 2019
Headed by former Van Gogh Museum Senior Conservator Ella Hendriks, an international team of specialists used the latest scientific techniques to examine Van Gogh's famous 'Sunflowers' painting. During the symposium on 21 June 2019, they shared the results of their research.
The morning sessions dealt with the perspective and painting of Sunflowers, while the afternoon sessions focused on imaging, discolouration and conservation.
The morning started with a presentation by Costanza Miliani, Senior Researcher at the National Research Council - Institute of Molecular Science and Technologies in Perugia. Her talk was on MOLAB (Mobile LABoratory), a European collaboration that facilitates on-site heritage research projects by providing portable equipment. MOLAB is a unique collection of high-performance, well-integrated portable experimental techniques, operated by five European facilities.
Two rounds of MOLAB research were conducted on Sunflowers:
- Firstly: spectroscopic point analysis was applied to complement the MA-XRF elemental mapping and provide a better understanding of the palette.
- Secondly: new methodologies were added, for example Vis-hyperspectral imaging, which offered insight into the chemical composition of the green, ochre-orange and purple hues of the painting.
2. Sunflowers in Perspective
Nienke Bakker, Senior Curator at the Van Gogh Museum, spoke about ‘Sunflowers in Perspective’. Vincent van Gogh painted five versions of his iconic Sunflowers. He made a total of eleven paintings of sunflowers between 1887 and 1889: four in Paris and seven in Arles in the South of France. This lecture sketched:
- the genesis of the series, the significance of the sunflower to Van Gogh, who claimed ‘I indeed, before others, have taken the sunflower’;
- how his paintings of this motif link to his friendship with Paul Gauguin;
- Van Gogh’s opinion of his achievement.
3. Painting the London Sunflowers
Catherine Higgitt, Principal Scientist at the National Gallery in London, talked about ‘Painting the London Sunflowers’. She presented the results of the technical investigation, which made it possible:
- to relate the pigments identified on the canvas to Van Gogh’s descriptions of the paints he used, outlined in his own letters;
- to conduct a better assessment of the condition of the London Sunflowers, particularly the impact of colour change, and thus Van Gogh’s original intentions in creating the work;
- to conduct richer materials-based, tonal and stylistic comparisons with the Amsterdam Sunflowers.
4. Painting the Amsterdam Sunflowers
Next up was Ella Hendriks, Professor of Conservation and Restoration of Cultural Heritage at the University of Amsterdam. Her talk was entitled She presented ‘Painting the Amsterdam Sunflowers’. Comprehensive investigations of Sunflowers have helped to elucidate different stages of the artist’s working process:
- making the canvas support;
- the first charcoal sketch;
- the palette used;
- the mixing and application of colour;
- the paint texturing and brushwork;
- a wooden strip extension added late in the painting process.
In comparison to the London picture, the Amsterdam picture is not just a straightforward copy of the original, but exploits a somewhat different palette and in particular other ways of mixing and applying paint to achieve a more stylized rendering and greater decorative unity.
5. History of conservation treatment
Ella Hendriks continued with the ‘Conservation of the Amsterdam Sunflowers: from past to future’. There were two main episodes of treatment performed in 1927 and 1961 by the Dutch restorer, Jan Cornelis Traas (1898-1984). Traas was the most important restorer for the Van Gogh family collection of paintings.
As Traas appears to have kept no records of his work, in-depth technical and scientific investigation helped understand what Traas’ former treatments of the Sunflowers entailed. Based on these insights, the condition of the painting was appraised and a conservation strategy defined.
The past interventions severely limit options for renewed treatment, so on balance the tendency is firmly towards preventive conservation with limited restoration measures.
6. Methods for non-invasive imaging
The afternoon kicked-off with Koen Janssens, Professor at the University of Antwerp. His talk was entitled ‘Emerging vs already established methods for non-invasive imaging of paintings’. Janssens presented current and future methods for performing non-invasive imaging of painted works of art at three different length scales, outlining benefits and disadvantages. The three length scales are:
- the macro or metre scale, which is the length scale at which the artists worked themselves.
- the microscopic level, which operates mostly on paint cross sections.
- the nanometre level, a length scale level that has not received a lot of attention in the context of the analysis of painter’s materials.
7. Chemical alteration and colour changes
Next up was Letizia Monico, Researcher at the University of Perugia’s Center of Excellence SMAArt and the National Research Council - Institute of Molecular Science and Technologies in Perugia. Monico’s lecture was entitled ‘Chemical alteration and colour changes: a focus on geranium lakes and chrome yellows’.
The colour changes due to chemical alteration of geranium lakes and chrome yellows is a challenging and complex issue affecting a number of paintings by Vincent van Gogh, including the Amsterdam Sunflowers. A description was given of how macro-scale non-invasive investigations, combined with advanced micro-analytical studies of cross sections and artificially aged mock-ups, provided evidence of chemical alteration of both geranium lakes and chrome yellows at selected spots on the painting. This research helped to identify some of the key factors that drive the degradation processes of pigments, which in turn can assist in the development of appropriate strategies of preventive conservation.
8. Painting a reconstruction
Muriel Geldof is Conservation Scientist at the Cultural Heritage Agency of the Netherlands. Charlotte Caspers is an artist and paintings conservator. They continued with ‘Searching for colour by painting a reconstruction of Van Gogh’s Sunflowers’.
Sunflowers has considerably changed colour over time due to the addition of two varnish layers, the accumulation of dirt on the surface of the painting and the use of light-sensitive red and yellow paint. To get an idea of how the painting looked shortly after it left Van Gogh’s easel, part of the work has been physically reconstructed using data from various research projects.
The colours used in the reconstruction were selected by using similar pigments to those in the original painting, as identified in the REVIGO (REassessing VIncent van GOgh) project. The first section of this lecture summarised the main factors that account for the colour change, while the second part discussed the practical painting process.
9. Surface layers
This double presentation described the characterisation of surface layers of Sunflowers. It was given by:
Klaas-Jan van den Berg, Professor of Chemical Aspects of the Conservation and Restoration of Cultural Heritage at the University of Amsterdam.
Piotr Targowski, Professor of Optics and Informatics, Nicolaus Copernicus University in Toruń.
Magdalena Iwanicka, Conservator, Restorer and Researcher at the Institute of Conservation Science, Nicolaus Copernicus University in Toruń.
The speakers started by explaining how to interpret the OCT tomograms before presenting and interpreting selected results. They subsequently presented a general overview of the stratigraphy of the surface varnish and the evidence supporting the local presence of products that altered the paint layers. The research has revealed the presence of two alkyd varnish layers, applied during the 1961 conservation work. Remains of dammar varnish, applied in 1927 and removed in 1961, were also detected.
10. Conservation treatment on the Amsterdam Sunflowers
The final speaker of the day was René Boitelle, Senior Conservator at the Van Gogh Museum. His talk focused on the conservation treatment conducted on Van Gogh’s Sunflowers.
The latest research into Sunflowers has made it abundantly clear that the condition has been profoundly affected by past conservation treatment. It is no longer possible to reverse past treatment, so it must now be accepted as part of the history of the painting. Options for new treatment are therefore also significantly reduced, and only minor work to improve the appearance of the painting was proposed. This entailed the removal of unsightly patches of beeswax on the surface of the painting and refreshing old, discoloured retouches by adding new retouches on top of the existing varnish layer.