Fading Red
Field with Irises near Arles
In this painting, Van Gogh's chief concern was with the colour contrasts. He focused on the red roofs and green trees, the strip of blue sky, and above all the contrast between the fields of yellow and purple flowers. Sadly, some of the colours are no longer what they once were. The red pigments in particular have faded over the years. This is due to the influence of light.
The conservator discovered this discolouration when she examined the painting without its frame. The irises at the bottom, close to the edge of the canvas, were far more reddish-purple. Since they had been partly under the frame and were scarcely exposed to light, they had retained their original colour.
Microscope photo of the paint at the bottom of the canvas where the frame covered the paint. In that section the reddish-purple has not become discoloured to bluish-purple.
Scan
Researchers then scanned the painting using Macro X-Ray Fluorescence Spectrometry (MA-XRF). This technique uses X-rays to reveal the distribution of chemical elements in the paint.
Van Gogh used the red pigment eosin, which contains bromine. The scan shows exactly where the artist used paint with this element. He used it in the flowers in the foreground and the trees on the horizon, for instance.
Old colour photo
The discolouration of the red pigments is confirmed by a colour photo of Field with irises from the 1930s. It is not a very good reproduction. Even so, it is striking that the irises in the foreground look far more reddish-purple in the photo than they do in the painting today.
The red pigments have evidently faded more since then. The colours in the old photo are probably more similar to the painting's original colours.
The dots in the foreground, just below the strip of irises, are white today. In the colour photo they still have a pinkish-red hue. The light-coloured dots in the fields, above the strip of irises, also originally had more colour.
Microscope photo of a spot where the paint is damaged. Immediately under the painted surface the paint is pink. On the surface it has faded to greyish-white.
