Part of Rembrandt’s masterpiece was scanned for Operation Night Watch. The technique employed can identify different pigments very precisely on the evidence of their crystalline structure. The scan can reveal the different crystalline structures of pigments at an atomic level. That enables the researchers to distinguish between the various pigments.
What technique was used?
The full name of the technique is macro X-ray Powder Diffraction scanning, or macro-XRPD for short. This augments the previous macro-XRF technique. Those earlier scans mapped the chemical elements of The Night Watch very precisely, but they could not distinguish between all the pigments. For example, they could not tell the difference between various types of lead white. They merely revealed the presence of lead. The second technique can do more than that.
How does the scanner do it?
The macro-XRPD uses X-radiation. It is the same radiation employed by a dentist or in a hospital. When the radiation encounters a pigment it is deflected and reflected. The way in which that is done differs for each pigment. So then you can see where each pigment is.
Unique in the world
The scanning was done jointly with the AXES Group of Antwerp University. The scanner that they developed, which is unique in the world, makes it possible to scan part of a painting without removing it from its location. Normally X-ray diffraction analysis is done in a laboratory with small fragments of paint.
Insight into the condition of the paint
The macro-XRPD scan also provides important information about the condition of the paint layers. It makes it possible to identify certain degradation products that appear as time passes. They arise through chemical reactions in the paint layers or on the paint surface. It is important for Operation Night Watch to map the degradation products and to examine them with a view to conservation treatment.