This large unfinished work by Frank Duveneck is in the paintings conservation lab to be examined.  The most obvious indication that the composition is unfinished is the unpainted figure in the center of the group, a small child sketched in with red-brown brushstrokes. 

One of the imaging methods our paintings conservator uses in an examination is capturing a digital image with a camera that filters out all light except rays in the infrared part of the spectrum.  In paintings conservation it’s used to expose underdrawing, the preparatory lines an artist made on on the prepared canvas or panel prior to actual putting down paint.  It’s a great technique to uncover the artist’s planning process, and maybe to show changes that the artist made during painting.  But there are some limitations, as this painting thoroughly demonstrates.  Because the unfinished figure of the child is sketched with paint that has a red tone, the infrared camera is unable to “see” it.  The figure disappears almost completely in the infrared image. 

In fact, if Duveneck used the same paint for underdrawing anywhere else in the scene, the infrared camera will not record it.  Here the absence of evidence is not necessarily evidence of absence.  It’s a fact that conservators and art historians need to keep in mind: If the infrared image shows no underdrawing, it does not mean there is no underdrawing present.  Though rarely is that so clearly demonstrated as it is in this particular painting!