Atelier Bouts | The Last Supper - Stratigraphy

In this display, we can see three paint samples taken from the central panel of ‘The Last Supper’. They show us the glazing technique that was essential to Bouts and other Flemish Primitives.

This particular technique involves applying multiple semi-transparent layers of paint on top of each other. These layers are called 'glazes'. A glaze consists of a relatively large amount of oil with a little bit of pigment. Each glaze has a slightly different composition. As light passes through the various layers, vibrant colours, deep shadows, and seamless transitions — characteristic features of the Flemish Primitives – are created.

In Bouts' workshop, his assistants would craft the paints themselves by rubbing pigment into oil. Each layer of paint had to dry for several days. So Bouts had to carefully plan the desired end result before putting down the first brushstroke.

We can find out how Bouts' applied his paints and their composition by studying paint samples. A scalpel is used to extract a miniscule paint sample, which is then cast in resin. This creates a cross-section in which the different layers are clearly discernible.

When paint samples are taken, no matter how small, a piece of the painting is removed. Therefore, it is justified only when other research techniques fall short. Samples are taken from the edge of the painting or in a lacuna in the paint layer. Furthermore, they are not discarded but remain available for further study and new research methods.

The paint samples of the blue and green cloak, for example, were taken more than 70 years ago. At the time, they were studied under a microscope. This led to tentative conclusions about the materials used, which were written down — as can be seen here on the table. Today, chemists can identify pigments and binders with great certainty.

On two of the three samples we see a thick white layer of lead white on the bottom, dating back to the 19th century. At the time, a restorer performed a very invasive procedure, called a 'transposition'. This involves removing the paint layer from the original panel and transferring it onto a new support.

To remove the original support, the restorer sanded the panel all the way down to the back of the paint layers. On that back, he applied a thick flattening layer of lead white. Heaffixed a mesh to the lead white layer, before finally glueing it to a new panel.