Klaas Jan van den Berg at CMOP final conference, Rijksmusem, 23-25 May 2018

Klaas Jan van den Berg (RCE/University of Amsterdam), Project Leader of CMOP 2015-18, at the final conference, Rijksmusem, 23-25 May 2018. Photo © Mikkel Scharff (CATS/KDK).

With the support of the Netherlands Institute for Conservation + Art + Science (NICAS) and AkzoNobel, the Conference on Modern Oil Paints took place between 23-25 May 2018 at the Rijksmuseum, Amsterdam, focussing on the complex and challenging subject of modern oil paints. The conference also marked the conclusion of Cleaning Modern Oil Paints (CMOP) project 2015-2018 with the University of Amsterdam, Cultural Heritage Agency of the Netherlands, Tate, Courtauld Institute of Art and the University of Pisa as the main project partners.

Logotype European Year of Cultural Heritage 2018

This conference was part of the 2018 European Year of Cultural Heritage

326 delegates from thirty-one different countries attended the conference, including conservators specialising in paper, paintings and sculpture conservation, as well as researchers, artists, curators and paint manufacturers. The programme consisted of 24 oral presentations and 25 poster pitches, which covered a range of subjects including: developments in artists oil paint technology; characterisation of modern-contemporary oil paints and paint surfaces; paint degradation and long-term stability; the artists’ voice and influence on the perception of curators, conservators and scientists; approaches to conservation and display; conservation of oil paintings; evaluations of surface cleaning options and practical surface treatments. The presentations demonstrated both the complexity of the subject and offered some critical developments in our understanding of the mechanisms behind the degradation phenomena encountered on modern oil paintings, which ultimately helps to inform conservation practice.

It is widely understood that modern oil paint formulations including pigment, binder and additives have, among other factors, a significant impact on the ageing and degradation phenomena seen in modern oil paintings. Several presentations and posters were concerned with developing an understanding of modern oil paint manufacture and the implications of formulation. Archival records were used to inform research into Winsor & Newton, Talens and BALM (later Dulux) paint formulations, as well as exploring how manufacturers worked with shortages of key raw materials such as linseed oil in times of war. Robert Gamblin (Gamblin Colours, USA) provided an insight into the manufacture of Gamblin artist oils and discussed their array of comprehensive tests designed to ensure paint quality and stability, both during and after production of each batch of paint.

Notable developments relating to the pigments that may be encountered in modern oil paint formulations were discussed, for example, the increasing use of synthetic organic pigments as non-toxic alternatives to traditional inorganic pigments such as chrome and cadmium colours. The sensitivity toward swelling and leaching of oil paints made with organic pigments was also noted. Additionally, several examples of new pigments introduced in the 21st century were discussed by Matthijs de Keijzer (RCE, The Netherlands). Many of the pigments that are used by modern artists’ oil paint manufacturers are produced for other industrial markets and are often of very fine particle size and can be coated using inorganic and organic compounds that may, for example, aid pigment-wetting but also modify the chemical properties of the pigment. These aspects may have a significant impact on paint ageing and deterioration, hence approaches for identifying surface-coatings on modern pigments were also discussed and evaluated.

Several studies involved the scientific characterisation of artists’ materials such as historical tubes of oil paint, binders, and pigments etc. This was combined with the technical study of various paintings including works by Karel Appel, Paul-Émile Borduas, Asger Jorn, Jean-Paul Riopelle, Georges Matthieu, René Magritte, Edvard Munch, Barnett Newman, Pierre Soulages, Clyfford Still, Pablo Picasso, Francis Picabia and many others; all of which helped explore relationships between paint formulation, artists’ technique and observed ageing phenomena.

Numerous examples of ageing phenomena were discussed by Klaas Jan van den Berg (Cultural Heritage Agency of the Netherlands and University of Amsterdam, and CMOP Project Leader) and other speakers. Discussions centred around: water sensitivity; soft, exuding and dripping paints; imbibed surface dirt; metal soap formation, with particular attention to zinc white paint and zinc soaps; delamination; cracking; discolouration; pigment-medium separation (particularly associated with French ultramarine).

Many informative talks discussing approaches to conservation treatment and decision-making process were also presented, where interviews with both artists and conservators were used to inform discussion. Ysbrand Hummelen (Cultural Heritage Agency of the Netherlands) delivered an insightful keynote lecture on the role of perception in cleaning, and the interrelationship between the creative process as informed through historically informed re-enactment, the process of cleaning and subsequent display. Lise Steyn (University of Amsterdam) discussed Robert Ryman’s paintings and the complexities associated with preserving or returning to their ‘original surface’, and the difficulty in documenting subtle surface effects such as gradations in surface gloss and light reflection. Examples of other complex conservation treatments were also presented; several presentations addressed extensive flaking paint and delamination caused by fluctuating environmental conditions or the formation of metal soaps.

The mechanical properties of modern oil paints were explored in one study by Cecil Krarup Andersen (KADK, Copenhagen) supported by CMOP Associate Partner the Getty Conservation Institute. Dynamic mechanical thermal analysis (DMA) and nanoindentation were used to study changes in mechanical properties of water sensitive paints under varying relative humidity conditions and in response to exposure to selected solvents. The influence of aspects of paint formulation such as pigment:medium ratio and additives such as alumina hydrate on paint mechanical properties were also investigated. These aspects are deserving of, and will be the subject of further research. 

The water sensitivity of modern oil paintings received particular attention, and the complexity of the phenomena was emphasised by a series of investigations of a diverse range of case-study paintings, including 24 paintings in Tate’s collection presented by Judith Lee (CMOP postdoctoral researcher, Tate) and a series of different paint mock-ups. In summary, causal factors relate to paint formulation (particularly pigments and oils), painting technique and environmental conditions. In some cases, magnesium sulphate heptahydrade or epsomite was cited as a cause of water sensitivity, and newly reported water-soluble sodium sulphate was noted in water-sensitive French ultramarine passages of an early twentieth century painting by Alexis Mérodack-Jeaneau (1873-1919). However, scientific studies suggested water sensitivity did not relate solely to the presence of water-soluble salts, and instead appears to be related to the degree of polymerisation of the oil binder and/or the nature of the ionomeric network formed upon paint curing. This aspect, alongside various other factors that influence the complex oxidation pathways of oil was discussed in detail by Ilaria Bonaduce, CMOP’s Principal Investigator for the University of Pisa.  

Systematic cleaning studies of water-sensitive oil paint mock-ups and test paintings were carried out as part of the CMOP project, and these explored possible cleaning approaches for unvarnished water sensitive oil painted surfaces. The use and relative performance of silicone pickering emulsifiers, microemulsions and rigid polysaccharide gels, made using tailored waters with adjusted pH and/or the use of selected surfactants and chelating agents were presented by Bronwyn Ormsby (Tate) and Miriam Gillman (Courtauld Institute of Art). In addition, the results of recent analysis considering the potential for residues of non-volatile cleaning agents left behind after cleaning were presented; the challenges associated with contextualising the relative significance, and long term consequences of small amounts of residues detectable only using highly sensitive surface techniques was also highlighted. Various application methods, such as the use of brushes, sponges and novel techniques as micro-aspiration, and the use of monoatomic oxygen were also suggested as additional possible avenues for treating highly sensitive surfaces. The challenge of removing varnish from water-sensitive oil painted surfaces was also mentioned.

The CMOP conference was an exciting opportunity for all parties interested in the conservation challenges associated with modern oil paintings to engage with some of the latest research in the field, and also to reflect on avenues for future work.

Significant progress has evidently been made in understanding the complex causes and phenomenology relating to various types of degradation phenomena in modern oil paintings and suitable conservation approaches. As was discussed by Aviva Burnstock (Courtauld Institute of Art), continuation of fundamental scientific research and technical study will be invaluable in informing the understanding of degradation phenomena, the condition and appearance of paintings, which will ultimately inform conservation practice. Finally, the proceedings of the conference will be published by Springer, to be available in 2019.

Judith Lee, Tate

June 2018