Infrared radiation is used to ‘see through’ paint layers that are impenetrable to the human eye. It passes through paint until it reaches something that absorbs it or reflects it back to the camera. Carbon black was commonly used to mark out the initial composition of paintings (known as an underdrawing) during this period and is very absorbent of infrared radiation. Therefore, if an artist has begun a painting by drawing the design in carbon black on a white ground, infrared reflectography (IRR) can make this visible.
Infrared reflectography showed that all four of the analysed Boschian paintings had extensive underdrawing and these underdrawings are clearly the work of different hands. For example, while the underdrawing of the Tallinn painting is in most parts very neat and careful the underdrawing of the Copenhagen painting is extremely loose and sketchy.
IRR also enables us to see alterations that the artist has made to the composition during the process of painting. For example, in the underdrawing of the Tallinn painting the hand of the apocalyptical clock (on the wall to the left of the temple) points optimistically to 11 o’clock but in the final painting it shows that the hour of judgement has arrived – the hand points to 12 o’clock. In the underdrawing of the Glasgow painting there is a figure fleeing from the temple, to the right of Christ, who remains almost entirely behind the pillar in the final scene. Additionally, IRR of the Tallinn painting revealed details in areas of the composition that had been overpainted at a later stage, including two pigs, a donkey and a goat.
The red circles indicate alterations made in the composition. Some alterations have been made during the original painting process, for example the hand of the apocalyptical clock points to 11 o’clock in the underdrawing but in the final painting it shows that 12 o’clock, the hour of judgement, has arrived. Other circles indicate areas where the original figures of the composition are covered with later overpaint.
