As part of our research project we used dendrochronology, a scientific method to date trees from their growth rings and to identify their provenance.

As expected, Bruegel carefully selected the planks he used as supports for his paintings. We discovered that the trees had grown in the Baltics, in areas that are now parts of Poland and Russia.

This was high-quality material. Baltic oaks grow slowly and ramrod straight, which means they produce particularly stable and long planks.

The earliest growth ring we found dates from 1201! This plank was used for The Tower of Babel.

However, the planks for The Return of the Herd, Peasant Wedding and The Birdnester are more recent. Here, the youngest growth ring we found dates from 1546. It is fascinating to note that at least 13 years elapsed between the youngest growth ring and the date on the painting.

We did not find any instance of planks from the same tree being used in different paintings. Sometimes, however, Bruegel selected planks from different trees for a single picture.

With other works, the changes in format are less apparent. Here, modern technologies and X-rays allow us to look inside the panel paintings. Among much else, they reveal dowels. These tell us about the painting’s original format.

We now know that The Birdnester was severely cropped, greatly altering its appearance.

Today, the birdnester has moved to the centre of the composition. While this may have achieved greater balance, the landscape has become less prominent.

Be that as it may, Bruegel’s carefully calibrated composition has been radically altered.

Today, we would call such interventions wanton. In light of these acts in addition to threats like fire, war and other external dangers, it seems almost a miracle that all these works by Bruegel have survived the centuries more or less intact. However, only four of his ’tüchlein’ have survived.

Originally, these ‘tüchlein’, which he executed in distemper on fine cloth, formed a seminal part of Bruegel’s oeuvre.

The paintings were also subject to conservation measures that were carried out with the best intentions. In the nineteenth century, eight of Bruegel’s paintings were cradled in an attempt to stabilize them. For this, the reverse sides of the panels were sanded, in many cases severely reducing their thickness. Slats were then glued onto the back of the painting. It was believed this would help reduce warping or stabilize fragile panels.

Of course, the reduction in the panel thickness often resulted in even greater problems.

Again, only Christ carrying the Cross has been spared and has retained its original thickness. This painting therefore plays a significant role in attempts to reconstruct the original construction of the panels.

This is why both its front and reverse sides are on display in the exhibition.

Using non-invasive methods like infrared-photography and infrared-reflectography to analyse the underdrawing was an important part of our research.

What do these findings tell us? Identifying the kind of underdrawing Bruegel executed, and knowing whether he stuck to it or altered numerous details, allows us to make inferences about his creative process.

In his early works, Bruegel paid special attention to and carefully delineated the countless miniature-like details he included in his compositions. We can see this for instance in The Battle between Carnival and Lent.

Here, we can identify delicate outlines, and even tiny details such as fingers or skewered sausages are delineated. When he painted then, Bruegel stuck closely to these underdrawings.

Bruegel’s brushstrokes become much freer, however, in his rendering of the stage – i.e., the houses lining the main square. Here, too, he executed underdrawings but then decided not to adhere to them.

It seems as though Bruegel began by freely creating a stage, which he then proceeded to fill with tiny details.

He changed his approach for Children’s Games, painted only a mere year after The Battle between Carnival and Lent. Here, Bruegel relied on preparatory drawings for far fewer details.

The Tower of Babel from 1563 represents a break in his use of underdrawing. Here, Bruegel felt free to ignore his own preparatory drawings, introducing countless changes while working on the painting.

Bruegel’s choice of carefully graded hues also helps to create the illusion of space and depth. He selected different palettes for each of his paintings. In The Battle between Carnival and Lent, for example, he used a surprising amount of black. Children’s Games was executed in pale, warm, glowing colours. The wintry mood in Hunters in the Snow is borne of warm yet frosty shades of blue.

What did the colours consist of? The pigments are typical for the time of Bruegel and his native country: the X-ray fluorescence analysis revealed earth pigments in the red and yellow ochres and umber, lead-tin-yellow, vermillion, bone black, plant black and, of course, lead white. Green was usually produced by mixing azurite and lead-tin-yellow.