When are paintings are more than meets the eye?
With the passage of time much may change – colors may fade or even disappear as the pigments that comprise paints degrade due to reactions with UV light and moisture. As a result, an artist's intention may not be immediately apparent.
Rembrandt's Homer (1663), currently housed in the Mauritshuis in the Netherlands, is such an example. Deterioration of pigments over the centuries has compromised the illusion of depth in the work. While in some areas colors have been preserved, others now appear a dull monochrome brown with details all but lost. Not only has the vision recorded by Rembrandt been partially erased, the intent behind his common use of smalt (a form of Co-bearing K-Si glass) is unclear. Smalt was used by some artists in the late 17th century as a blue-pigment substitute for the more expensive ultramarine. But was this why Rembrandt reached for this part of his palette?
The mid-17th century painting of the Greek poet Homer was scanned using Bruker's M6 Jetstream µXRF (MA-XRF) as part of the REVISRembrandt project, revealing extensive use of smalt (seen in Co maps like the one below). Researchers interpret that instead of using smalt for its blue color, Rembrandt employed it to add volume and texture to paints, not only providing depth to colors but speeding up the drying process to allow him to develop and maintain texture. The MA-XRF scans also show details previously lost to the naked eye, now revealed in maps of Pb (from lead-white pigments). This study shows the power of elemental mapping techniques to delve into the rich history of such culturally important art works.
The role of smalt in complex pigment mixtures in Rembrandt’s Homer 1663: combining MA‑XRF imaging, microanalysis, paint reconstructions and OCT
A. van Loon, P. Noble, D. de Man, M. Alfeld, T. Callewaert, G. Van der Snickt, K. Janssens, J. Dik
Heritage Science, 8:90, 2020