Titanium white: a villain to other pigments?

The Ateliergebouw, or Studio Building also hosts many PhD students. Birgit van Driel is one of them. She works on the degradation of Titanium White paint. Titanium white paints were introduced to the market in the beginning of the 20th century  and increasingly replaced the rather toxic lead white paints. These new paints with their excellent hiding power were used by, among others, Jackson Pollock and Pablo Picasso.

Birgit explains how Titanium white containing paints have a lot of positive properties but can also, depending on their composition, cause damage when exposed to ultraviolet light. The underlying property that causes this damage is called photocatalytic activity. When titanium dioxide absorbs UV light, this can start degradation processes affecting the surroundings of the white pigment, such as the binding medium, making the paint layer brittle, matt or chalky. A chalky paint has unbound pigment at the paint surface due to degradation and disappearance of the binding medium and looks similar to chalk on a chalkboard, hence the name. The degradation can also  have an impact on other pigments present in the paint layer, leading for example to fading. However, it is important to note that not all titanium white pigments have this property and present day pigments are mostly of good quality.

Birgit’s PhD project aims to better understand degradation processes caused by titanium white pigments and to make it possible to predict and prevent them. As the works of art containing titanium white are relatively young, this research could potentially be used to prevent degradation and contribute to the preservation of 20th century art.

c
Paint mixtures prepared for artificial aging

Birgit used artificial aging to study titanium white paints. To do this she made reconstructions of paints containing titanium white and a coloured pigment mixed with linseed oil and an added drier.

d
The strips of paint are articficially aged

These self-made paints are subjected to extreme conditions of accelerated aging, using UV light, to investigate their aging behaviour. In this case, she investigates the effect of two types of titanium white pigments (‘good’ and ‘bad’ quality) on a set of coloured pigments: Alizarin Lake, Scarlet Red, Cadmium Yellow, Ultramarine and Prussian Blue, all pigments extensively used in artists’ paints. Initial evaluation of the results, though still work in progress, suggests that all the other pigments in this set, with the exception of Prussian Blue, are stable and not sensitive to degradation initiated by the presence of titanium white. In some cases they even delay binder degradation.

Using reconstructions as a research tool often helps us to understand the behaviour of materials over a long period of time.

With thanks to Birgit.

Erma

Birgit van Driel has obtained her bachelors in Chemical Engineering from TU Delft, with a minor in Art History from the Free University in Brussels and a Masters in Material Science from the Ecole Polytechnique Federale de Lausanne. During her Masters she did an internship at the Museum of Modern Art in New York, where she operated the Bruker M6 XRF-Scanner. She is currently in the 3rd year of her PhD. This research is carried out under collaborative supervision by the Rijksmuseum, TU Delft, the cultural heritage agency of the Netherlands and AkzoNobel.

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