News #

Becoming Blue

When Angela Jørgen Wadum study the many Dutch and Flemish paintings collected by Johannes Hage or later added to The Nivaagaard Collection, they scan the paintings with an infrared CCD camera (see story # 2) on a routine basis.

Next, the researchers need high-resolution recordings, such as infrared and false color images. Conservation scientist Camilla Perondi, who specializes in photographic documentation via multispectral recordings that can record more wavelengths than the human eye can see, is then involved in the special process.

Blue pigments – a complicated story

The many different blue pigments that painters have used throughout history have varied over time and in order to determine the time period of a painting they are essential to uncover. Prussian blue, for example, is a marker for paintings produced after 1706, when it was first produced in Berlin and immediately became hugely popular as it was cheap and had an excellent hiding power.

Apart from infrared imaging Camilla also performed multiband analysis of paintings to investigate the use of blue pigments in the composition. Although the imaging techniques are not inherently selective and do not provide precise identification of pigments or materials used in an artwork, they assist in narrowing down the range of possible materials to a smaller group based on their spectral response to different radiations.

Nicolaes Pieterszoon Berchem, Mountain Landscape with Cattle Herders

Blue pigmented mountain landscape

I undersøgelsen af det store italienske landskab af Nicholas Berchem (1622/1623 – 1683) observerede Camilla, at det infrarøde billede udviser et stærkt reflekterende signal for det blå pigment på himlen, som udmønter sig i en lys rosa i det falsk-farve kompositte billede.* Der er flere kandidater, der reagerer på denne spektrale adfærd, nemlig cerulean blå (efter 1790), cobalt blå (efter 1807), indigo (fra 4000 f.Kr.), Lapis Lazuli (efter 1300) og smalte (efter 1500).

Preussisk blå er derimod kendt for at reagere på infrarød stråling med lav reflektion (~ 10%), hvilket resulterer i et mørkt signal i det infrarøde billede og en mørk lilla, næsten sort, respons på de infrarøde falsk-farvekompositter. Tilstedeværelsen af preussisk blå er derfor udelukket som det pigment, der blev brugt til at male himlen.

What’s in a blue coat?

The scientists were also interested in investigating specifically the blue coat lying on the back of the white horse in the right foreground. Visually the colour appears as an intense dark blue. However, in the infrared and UV reflected images, the pigment acquires a dark tone. Such a response is encountered with the pigments Azurite (after 1100) and its synthetic version Blue Verditer (after 1500), Vivianite (after 1500) and for Prussian Blue.

The retention of the blue hue in the infrared false colour composite strongly indicates the use of Prussian Blue for this detail. This information, coupled with art historical evidence (more about this at a later stage) points to a necessary reassessment of the painting. We now believe that it is an 18th century copy painted at least quarter of a century after Nicholas Berchem’s death.


Nikon D800 and Nikon D800 full spectrum coupled with Nikon Nikkor 135mm f/3.5 AI; VIS: MidOpt BP550; IR 850: MidOpt BP850; UVR: MidOpt BP365 + MidOpt BP485; 2x Elinchrom ELC500 + Softbox 55x75 cm; 2x Madatec UV LED 365nm; Tonal correction with an array of Zenith Polymer® Diffuse Reflectance Standards (99%, 60%, 25% and 2.5%). Art + Image

*False color image processing is a non-invasive technique that combines and rearranges the color channels from one or multiple source images that results in a final composite image. The colors rendered in this resulting image do not match those that would be observed naturally by the human eye. These methods help visualize information not otherwise discernable which can aid in interpretation of media and materials present and inform further scientific analysis, conservation examination, and scholarly research.


The text is an expression of the discoveries made at the time of publication.

We reserve the right to make changes as new information from the still ongoing research project may occur.

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