A responsible conservation process starts with written and photographic documentation. Choices with regard to the conservation process arise from the primary research findings. Every painting has a different (creation)history which influences the current condition of the materials used to create it.

Material-technical research complements the art historical and painting-technical research. When determining the condition of paintings, the materials applied are identified and the current condition they are found in is accurately determined. Subsequently, the properties of the materials identified can be linked to the painting technique of the artist who created the object being studied.

Painting materials

Painting materials provide a great deal of hidden knowledge, because paints, thickening agents and drying agents are indispensible to painters for the creation of a durable depiction. Particular paints belong to particular eras. They can be of natural origin or of artificial composition. The application of colours depends on the period, studio traditions, contemporary convictions, learning processes, ‘secret’ recipes and personal preferences. The supply of raw materials for pigments could be temporarily halted by war or changing economic or industrial demands and pigments were sometimes removed because, for example, they were highly poisonous. The paints used can be determined using measuring techniques. The paints’ place in a particular phase of the painting’s construction can also be of importance to the conservation process.

The painting materials utilised also reveal the artist’s knowledge of materials. For example, some paints or combinations of pigments can lead to discolouration in a painting over time. This is a natural reaction which is undesirable as attested to by painters’ manuscripts from the past.((1) Recognising and interpreting these chemical or physical changes has become an important part of a restorer’s daily practice and can lead to changed art historical insights.(2)

Analysis of the auxiliary, drying and thickening agents is also important. Both the composition and the location of the agents on the object under scrutiny are examined. This can not only vary per painter, but also per period within that painter’s oeuvre.
Finally, it is important to study the natural and/or artificial ageing of materials with a view to interventions and future conservancy.

In this study the priority is on:

Pigment identification for the paints utilised.
Cross section of the painting-technical structure

Light techniques

Visualising the painting-technical structure using modern light techniques is of crucial importance to research into paintings. Making, among other things, the internal structure of a paint layer visible provides more insight into the painting-technical structure, the processing and the tools used. It can also provide insight into any possible artificial and/or natural processes which have taken place since the ceiling paintings were created. The techniques used in this study will be non-destructive.

Our research will use:

UV fluorescence

UV fluorescence is a surface visualisation technique. The wavelength limit for long-wave, ultraviolet photographs lies in the spectrum between 320 and 400 nanometres. In order to take a photograph, the painting’s surface is lit by two UV light sources.
The colour temperature of UV scans is not standardised. This means that the exposure and shots always differ. That is why you should always be very careful about comparing two UV scans.
These scans are primarily used to make retouches, the varnish layer, partial varnishes and varnish remnants visible. UV fluorescence can therefore reveal restorations and the painter’s own later additions to the top coat. Later manipulations of the surface such as retouches or varnish additions result in discontinuity of the fluorescence and look lighter or darker depending on the absorption or the level of reflection of the thickening agent or paint used.

Infrared reflectography

The long-wave wavelengths in the infrared part of the spectrum provide the opportunity to reveal the underdrawings on a monitor using a so-called vidicon camera. Long-wave infrared starts at 780 nanometres. The wave length limit for infrared reflectography is between 1900 and 2400 nanometres. Painted underdrawings which have a high saturation of the carbon in the pigment are suitable for this technique. The extent to which the underdrawing can be seen is largely determined by the reflection of the white ground. Furthermore, the ‘legibility’ of an underdrawing depends on a dark, carbon containing pigment for the drawing, the thickness of the paint layer applied over the top and the type of pigment used for the latter.

X-ray film

A painting can be X-rayed. The wavelength limitation is between 0.01 and 4.5 nanometres. This enables underlying structures in the paint layer to be revealed such as the working of the first grounding, underpainting and later modifications to the composition. Furthermore, the black & white images make it easy to study the individual brush strokes in both the top and base layer. This is only possible if the layers contain heavier elements such as lead.
in cooperation with Applus/RTD the ceiling painting will be X-rayed in its entirety. As far as we know, this will be the largest X-ray ever made of a seventeenth-century Dutch master. This cooperation will be recorded on video and will be screened in the near future.


The storage conditions in the Bol room are not ideal for the ceiling paintings. The supervisory committee has decided, to consult with the Rijksdienst voor Cultureel Erfgoed to optimise the current situation.
Report on the findings to follow.

1: Margriet van Eikema Hommes, Changing Pictures, Londen: Archetype Publications Ltd., 2004. (back)

2: J. Dik, M. den Leeuw, W. Verbakel, R. Peschar, R. Schillemans en Henk Schenk, 'The Digital Reconstruction of a Small Discoloured Painting by Hendrick Ter Brugghen', Zeitschrift fuer Kunsttechnologie und Konservierung, 16, 2002. (back)

Text: © Milko den Leeuw – Atelier voor Restauratie & Research van Schilderijen