15 Jan 11

The Poussin Project

The revelations of UV photography

As we draw closer to the cleaning of the Crossing of the Red Sea we turn our attention to UV photography. A quick glance at an image of the painting under ultraviolet light is enough for a conservator to learn some of the critical issues regarding its surface, especially the condition of the old varnish and the previous restorer’s work.

When paintings are placed under UV light they fluoresce in a particular way which looks very different to their appearance under normal lights. Apart from the overall bluish tone it gives to the picture, we can often perceive a slightly milky layer blanketing the colours and tones. This effect usually comes from the varnish layers. Old tree-resin varnishes such as dammar or mastic typically fluoresce a pale green colour, and this becomes more pronounced as the varnish gets older. The fluorescence visible on the UV image of the Crossing of the Red Sea is what one would expect to see in a fifty-year old varnish.

However, what is more notable about this photo are the very dark patches which interrupt this overall pale effect. They are indicated with the arrows in the photo below:

These dark areas are patches of retouching applied by Horace Buttery – the previous restorer – in 1960. The extent of dark areas of the clouds and trees tell us that he needed to do quite a lot of work in those areas, suggesting that the underlying original paint was damaged or worn some time earlier.

When we look at a detail from the UV photograph we can see that there are also considerable smaller retouchings in the sky which are not visible under normal light:

These old damages and repair are not uncommon in canvas paintings as old as the Crossing of the Red Sea , so are not cause for alarm. What they mean in terms of the treatment ahead is that the cleaned painting will reveal the wear and tear the painting has endured, and that the upper part of the painting will require more work to reintegrate than the lower part containing the figures, which is in a better state of preservation.