Conservation of Devout Men Taking the Body of Saint Stephen, dated 1776, by Benjamin West (American, 1738–1820):
Infrared Reflectography (IRR)

How does it work?
Infrared reflectography (IRR) utilizes wavelengths in a region of the electromagnetic spectrum just beyond the red end of the visible light spectrum. These wavelengths are of lower energy with longer wavelengths than visible light. Infrared radiation is detected and recorded with thermal imaging devices, a method originally developed for the military.

What do we see?
Infrared reflectography allows conservators to see what lies beneath the painting’s visible paint layer. Reflected infrared energy makes most pigments more transparent than when viewed with regular light. Because black pigments are notable exceptions to this rule, this technique can expose certain preparatory underdrawings and underpaintings. In some cases, IRR reveals where the artist diverged from the initial planned composition or made alterations.

So what do you see?
Examination with infrared reflectography confirms that Benjamin West began the altarpiece with a relatively robust underdrawing laying out the composition. The consistency of the line and its tapering edges suggest that he made the drawing with a liquid medium, likely paint that had been thinned enough to produce a flowing, fluid line.

At left above is a detail of Saint Stephen’s face in visible light. At right is an infrared reflectograph of the same area. In visible light, a light gray line just to the left of Stephen’s right nostril can be seen. The paint is very thin here, causing a small part of the underdrawing to be visible in normal light. In the IRR image, the underdrawing is clearly evident in Stephen’s upturned face. Note the original position of the lips, which were shifted slightly in the final painted image.