Researchers at the Rijksmuseum, in collaboration with some of their peers from VU Amsterdam, used a new measurement method based on techniques from biomedical and natural sciences to learn more about why cracks appear in layers of paint. One of the aims of the multidisciplinary team is to help the development of restoration and preservation techniques.

05/15/2020 | 5:29 PM

If you look closely, you will see them on almost every historical painting — lots of tiny cracks in the paint. Sometimes the craquelures are barely visible, sometimes they are prominent. If too many cracks appear, a painting can end up irreparably damaged.

Collaboration leads to new measuring technique
To learn more about why the fine cracks appear, and to better understand the behaviours of different binding agents, additives and pigments that make up layers of paint, researchers at the Rijksmuseum sought the assistance of Davide Iannuzzi’s research group at VU Amsterdam. Together they developed a new measuring technique, based on nanoindentation used in biomedical research. The results of their pilot study, partially financed by the DE Heus/Rijksmuseum Fonds, were recently published in Scientific Reports.

Internal stress
“A painting consists of various layers, including the canvas, the ground layers, the paint and the varnish,” explains Mathilde Tiennot, postdoctoral research fellow in the Conservation & Science department of the Rijksmuseum. “These layers have different properties, which induces internal stresses between the layers. For example, once a painting has dried, two layers that lie on top of one another can have differing elasticity. This creates stress, for example due to changes in relative humidity in the air or movement of the canvas.”

How does it work?
The measuring technique works as follows: a glass microsphere is attached to a microscopic cantilever spring one millimetre long. To take a measurement, the sphere is pressed onto the layer of paint. The instrument measures both the bending of the cantilever spring and the force that is exerted. The relationship between the two indicates how stiff or flexible the material is on that particular spot.

From skin to paint
Two years ago, Erma Hermens, full professor at University of Amsterdam and senior researcher in Technical Art History at the Rijksmuseum, arrived at the idea of approaching Davide Iannuzzi and his research group at VU Amsterdam. “I was wrestling with the question of how we could learn more about craquelures and how the mechanical properties of the different layers of a painting could be measured without damaging the painting. After doing some research, I contacted Davide Iannuzzi, who had developed a measuring device for determining the mechanical properties of soft tissues, such as brain tissue and skin. Could the same technique also be applied to paintings? Despite all the challenges we faced, we decided to carry out a pilot experiment.”

Portable measuring device
The multidisciplinary team applied the method to paint samples from a 17th century painting by Jan Weenix in the Rijksmuseum collection that showed a lot of cracks. The researchers are also working on the application of the method in other projects that require the analysis of the mechanical properties of paint, for example to improve the understanding of historical paint formulas where glass has been added, or the behaviour of modern types of paint. “The new measuring technique is still in full development, the ability to measure the stiffness and elasticity of layers of paint is a first step,” says Hermens. Iannuzzi’s team is currently working on a portable measuring device for nanoindentation on various materials. Hermens explains, “It would be great if you could bring this kind of instrument to the museum to test objects on site.”

Mathilde Tiennot at work in the lab
Main picture: Portrait of Silvester van Tongeren, Jan Weenix

Mathilde Tiennot aan het werk in het lab

 Hoofdbeeld: Portret van Silvester van Tongeren van Jan Weenix