The Red Ballet Skirts is one of 23 pictures by Degas in Glasgow Museums’ collection. Made around 1900, three ballerinas in vibrant, red tutus are shown resting off-stage, leaning on the scenery or otherwise taking a moment to themselves.

Because Degas often applied his pastel thickly and in multiple layers, we can only catch a glimpse of those applied lower down. Ultra violet photography allow us to look beyond what we see on the surface, revealing Degas’s otherwise hidden techniques. In the example of ‘Red Ballet Skirts’, the presence of layers is further revealed through UV photography, where we can see layers of drawing otherwise hidden or obscured beneath the top layers, including broad, black strokes.

UV photography also shows bright fluorescent areas, seen in the skirts, on the dancers’ bodies, and the edges of the picture. We would not expect these edges to fluoresce in this way, and what we are likely seeing is a fixative showing up under UV.

This gives us clues about how Degas ensured the many layers of pastel laid down on a surface did not smudge. The artist was known to use a fixative obtained from an artist called Luigi Chialiva. This fixative was made to a ‘secret formula’, and was designed to give neither a dull appearance to the pastels, nor an overly shiny one.

Analysis across Degas’s pastels has shown the presence of casein, a milk protein, however it is likely that- as with many areas of his art- Degas experimented with a number of different options. The presence of fixative, appearing in the florescent areas of ‘The Red Ballet Skirts’, serves above else to reassure that the artist took pains to secure the many layers of pastel.