Re-evaluating museum guidelines

‘There are basically two types of conservation: remedial, where you address something that has already happened to an artwork, and preventive, where you try to avoid damage in the first place,’ says Duivenvoorden. ‘The latter is often achieved by tightly controlling the environment around paintings. But the amount of energy consumption associated with indoor climate control is currently leading museums to re-evaluate their guidelines on this issue. Of course, given the importance of the paintings involved, museums are cautious about applying changes without knowing what effect they could have on the artworks in their care. So we need to gather as much information as possible about the role that environmental conditions can play in a painting’s conservation status at a given moment.’

Four years ago, Duivenvoorden set out to study the relationship between humidity in the environment and the concentration and distribution of water inside oil paintings, a topic on which there is surprisingly little quantitative data currently available.

How water behaves in paintings

Oil paintings are complex objects and always changing, due to their environment and the way they have been treated in the past, but also due to the inherent chemistry of the paintings themselves. Once dry, oil paint is made of pigment particles that are held together by intricate molecular networks. Chemical reactions in these networks can lead to increased fragility after centuries on a canvas. To understand how exposure to water changes a painting, conservators need to understand how water is transported through the various layers of the painting and how it behaves at each level. Duivenvoorden: ‘Additionally, you need to be able to detect these molecular changes in the painting in the first place. If you don’t even know the painting is changing, you can’t begin to understand how or why it is changing.’

‘I was able to study two very similar paintings from the Frans Hals Museum, both painted in 1663 by Jan de Bray,’ says Duivenvoorden. ‘One of the two was exposed to liquid water in the 19^th century due to a leak in the roof when the collection was housed in Haarlem’s Town Hall. This didn’t do the painting much good, but this unfortunate incident has now given us the chance to study in detail what rather extreme water exposure can do to such a painting.’

Bumps and blisters

Duivenvoorden was able to link the accelerated growth of so-called ‘lead soap protrusions’ (bumps or blisters that can rise up and distort a painted surface) in the damaged painting to the water exposure it had suffered. She was also able to show how water can group together near the surface of pigments within a paint layer and enhance the chemical reactivity in that location. ‘Essentially, when a painting is very wet or humid, chemical reactivity will accelerate. This link between water and reactivity was observed before, but until now we didn’t actually understand the mechanisms behind it.’

Duivenvoorden’s study gave the team at the Rijksmuseum valuable insights into the ways in which water is being transported through the layers of Rembrandt’s monumental painting The Night Watch, as part of the museum’s Operation Night Watch. ‘We’re trying to evaluate the environmental response of The Night Watch – trying to make a direct connection between the humidity in the museum gallery and the exact concentrations of water inside all the layers of the painting. Hopefully, this work can help inform conservation guidelines in the future. Ideally, museums will be able to begin to decrease their carbon footprints in full confidence that they are not risking damage to the invaluable cultural heritage they house.’

Defence details

Jorien Duivenvoorden, Transport and behaviour of water in oil paintings. Promotor is Prof. dr. K. Keune, co-promotor is Dr J.J. Hermans.

Time and location

Friday, 14 February, 10:00-11.30, Agnietenkapel, Amsterdam