Infrared camera brings to light alterations in Renoir painting

Hidden wine glasses on the table, two pairs of eyes on one face, a completed landscape beneath an awning—these are all elements in Auguste Renoir`s painting Luncheon of the Boating Party that do not appear in the final version. These concealed items, indicating the progression of the artist`s working process, were uncovered by an uncooled infrared (IR) camera developed by Sensors Unlimited (Princeton, NJ).

Marshall Cohen, vice president of Sensors Unlimited, says, "When you look at art work, what you are seeing is the visible reflection of the pigment. . . . But what you see in the visible does not tell you at all what it looks like in other wavelength bands. In the near-IR, particularly the 1- to 2-µm band, many of the pigments used in oil painting are translucent."

The world`s most famous painting after the Mona Lisa shows 14 people socializing on a covered balcony during lunch at an outdoor restaurant. Renoir painted directly on the canvas but continued struggling with the compositional elements--facial expressions, hat positions, wine glasses--as the IR images of this technical study indicate.¹

In the image above, the IR reflectogram shows the presence of a developed landscape below the awning (A), as well as the entire span of a railroad bridge (B). Brushstrokes across the bearded man`s forehead indicate that the hat was repositioned several times (C). In the reflectrogram of the table setting below, glasses from an earlier rendition (A, B, C) were painted over, and the a stemmed glass (D) was transformed into a wine glass.

Other applications

The development of the 128 × 128-pixel indium gallium arsenide focal-plane-array (FPA) camera was partially funded by the Ballistic Missile Defense Organization Small Business Innovation Research program. "[Art inspection] is one of our smallest markets," says Cohen. "Yet, this is the most fun."

The camera can profile laser beams within the 1- to 2-µm wavelength band. A system that uses the camera to see clear ice on an aircraft wing should be ready for testing at airports this winter. This is similar to "black" ice on a roadway, says Cohen. It is impossible to see in visible light, but not in the near-infrared.

"We pushed the technology into large-area devices," says Cohen. "We are about to introduce a 320 × 240-pixel FPA and camera. This is the size of a 2/3-in. charge-coupled device; it is the largest device ever produced in the indium gallium arsenide material system and has very high resolution." These will be ready for market by fall of this year.

Reference

I. E. Steele, "Achieving the Composition in Luncheon of the Boating Party," The Phillips Collection`s 1996 Exhibition Catalogue.