The chemistry of oil paintings

A true Science in Society

23 March 2015

At the fifteenth Dies Natalis of the Faculty of Science on Thursday 26 March chemist Piet Iedema of the Van 't Hoff Institute for Molecular Sciences (HIMS) will lecture on the chemical aspects of decay in oil paintings. Iedema leads the research project Paint Alterations in Time (PAinT), which fits perfectly with the theme of the Dies celebration: Science in Society.

In the last two decades the investigation of chemical decay in oil paintings has become a crucial condition for innovations in conservation science. Amsterdam researchers Prof. Jaap Boon, Dr Katrien Keune and Dr Annelies van Loon were among the pioneers who revealed chemical decay in many masterpieces worldwide.

According to Iedema, who introduced research in this field to HIMS, museums all over the globe now recognise the ongoing chemical deterioration of their paintings. A sense of urgency is felt for research into the underlying phenomena. Already it has been shown that some conservation treatments of the past–however well-meant–have caused more harm than good.

prof. dr. P.D. (Pieter) Iedema

Prof. Piet Iedema. Photo by Jan Willem Steenmeijer.

'The good news is that detailed knowledge of the transient state of paintings will help optimize conservation treatments', says Iedema.

'However, we are dealing with challenging chemical problems that cannot readily be solved. There is no simple solution at hand.'

Metal soaps

Iedema explains that one of the major problems of oil paint lies in the binding medium. Based on linseed oil, this has a strong tendency to react with metals in the coloring pigments. The resulting metal soaps can lead to discoloration, increased transparency, whitish hazes and visible protrusions at paint surfaces.

To study the pigment-binder systems in great detail in 2012 the PAinT project was started. In this the HIMS researchers collaborate with Dr Maartje Stols-Witlox of the Conservation and Restoration department at the Faculty of Humanities. PainT, an acronym for Paint Alterations in Time, forms part of the Science4Arts Program of the Netherlands Organisation for Scientific Research (NWO) and involves almost all major Dutch museums.

Metal soaps in View on Delft

Metal soaps in the famous painting of the Delft skyline by Johannes Vermeer. Research performed by PAinT researcher Dr Annelies van Loon.

The PAinT team explores the chemistry and degradation from the moment of paint application to the current aged state of the centuries-old masterpieces now on display in our museums. The researchers combine detailed analysis of historical paint samples with paint reconstruction, chemical model systems and computer modelling. Since it houses expertise in all these fields, the Van 't Hoff Institute for Molecular Sciences provides the perfect environment for the multifaceted PAinT research.

Comparing spectroscopic data

Iedema reports small but important steps in understanding the ageing of the oil paint. For instance, PAinT PhD researcher Joen Hermans discovered that the ageing paint layers show remarkable similarities to so-called ionomers. These rather well-known materials, with fascinating properties, can be considered as metal-coordinated polymer networks. Iedema wants to link the existing knowledge about these ionomeric networks with PAinT's new insights into the mature oil-containing polymeric networks. He expects this will lead to a significant increase in the understanding of migration and degradation processes within paintings. 

Metal soap formation

Formation of metal soaps.

The PAinT team is now comparing spectroscopic data from model ionomers with paint samples from Dutch masterpieces. For this the advanced analytical techniques available at HIMS are used, with the active involvement of professors Peter Schoenmakers, Garry Corthals and Maarten van Bommel.

Iedema: 'This is a vital step towards a detailed understanding of the current appearance of paintings and it will enable the prediction of their future manifestation.' As a result, the PAinT project will yield crucial information about the effects of conservation treatments and of environmental parameters, such as temperature and humidity, on paint degradation. This will lead to improved conservation treatment guidelines.

New projects

The square man, Karel Appel, 1951

The painting "The square man" by Karel Appel (1951, Rijksmuseum) is one of the works that will be investigated in the H2020 research.

Iedema is already very pleased that several new projects have sprouted from PAinT. He mentions a PhD research project with the Rijksmuseum and AkzoNobel, regarding the ‘ultramarine disease’, the discoloration of Lapis Lazuli ultramarine pigments in oil paint. Recently Katrien Keune was granted a European H2020 PhD-project concerning degradation phenomena in modern paintings, which are often made with industrially produced pigments.

Iedema expects a further strong impulse to multidisciplinary art-related research from the establishment of the Netherlands Institute of Art Sciences NICAS. This is founded by NWO with the main partners being UvA (both the faculties of Science and of Humanities), Rijksmuseum Amsterdam, TU Delft and the Cultural Heritage Agency of The Netherlands.

S4A-PAinT Project

Published by  HIMS