Infrared reflectography at the KIK-IRPA

Types of object examined

- Paintings on panel
- Paintings on canvas
- Painted shrines and altarpieces

Selecting the most appropriate method

Infrared reflectography is generally the most suitable method for the visualisation of underdrawings and can also contribute to the study of painting techniques and to record the extent of later retouching. 

Equipment

For infrared reflectography, we use a thermal camera sensitive to near infrared radiation in the 900-1700 nm spectral range. We add narrow bandwidth filters to avoid reflections. We have added an external filter (1100-1700 nm) to avoid reflections. The camera has an indium gallium arsenide (InGaAs) captor with a resolution of 640 x 540 pixels. It uses a Peltier cooling system. 30 images are produced per second, and data transmission is done by an Ethernet Gigabit interface (GigE Vision, normalised). We have two objectives, which we select according to the required resolution: a 35 mm lens, used with a 1100-1700 nm filter, and a 55 mm lens, used with a 1500-1730 nm filter.

 

 


 

For digital infrared photography, we use a Hasselblad H4D-200MS, which gives higher resolution images than infrared reflectography, but with a lower spectral range. This technique gives excellent results when the paint layer is thin and the pigments are not strong absorbers of infrared.


Procedure: infrared reflectography

Recording the image: The entire surface of the painting is recorded as a series of small images. We use a motorised rail system for precise positioning of the camera. The platform moves vertically, horizontally and diagonally and has a laser-guided forwards/backwards feature to maintain a constant distance between the camera and the painting. Warps or irregularities in the painting’s surface are thus accommodated, ensuring that images are focused and remain the same size. Capturing images is carried out manually, by remote control, using wifi. The operator remains with the painting at all times during examination.
Mosaics: The recorded images are digitised and assembled using Adobe Photoshop or PTGui, resulting in high quality, seamless infrared reflectograms.
Storage of images: Raw and processed images are stored on the Institute’s picture archiving system.

 

On-site work

Our infrared reflectography and digital infrared photography equipment is mobile and can accommodate the majority of situations. Works of art that are glazed are difficult to record successfully.

 


Head of the unit: Christina Currie, work leader
Infrared reflectography: Sophie De Potter, technical expert