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Friday, May 6, 2016

Brooklyn Museum: Visible-Induced Luminescence Imaging


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Brooklyn Museum wrote:
As you’ve seen in several of our recent posts on the Della...
VIS image of mummy portrait 1996.146.9


VIL image of mummy portrait 1996.146.9


VIS image of Stuart Davis, “Landscape with Clay Pipe”, BKM 1992.11.4


VIL image of Stuart Davis, “Landscape with Clay Pipe”, BKM 1992.11.4

As you’ve seen in several of our recent posts on the Della Robbia and Stuart Davis conservation projects, we have recently been doing a lot of multispectral imaging in the lab. One of the techniques that has been particularly informative is called visible-induced luminescence imaging.
Visible-Induced Luminescence Imaging, known as VIL for short, was introduced by Giovanni Verri in 2009, and involves the excitation of pigments on object surfaces with visible light, and the photographic capture of the resulting emission of infrared radiation. Specific pigments, including Egyptian blue, Han blue, Han purple, and some cadmium pigments, emit infrared radiation when excited in the visible range, creating visible-induced luminescence. This means that while the rest of the image will be dark, the particles emitting luminescence will “glow” a bright white color.
This phenomenon can be captured in an image with off the shelf camera equipment. A modified camera that is capable of capturing images in the infrared region is needed, as well as special lens filters and a visible light source. At the Brooklyn Museum we use LEDs.
This technique can help answer a variety of questions, such as mapping the presence of specific pigments across a surface. In the image of the coffin below, the glowing pigment can be identified as Egyptian blue. VIL can be helpful when looking at ancient varnished surfaces such as the one above, where blues may be mistaken for greens because of the yellow hue of the varnish. And it can also help identify the presence of luminescing pigments in paint mixtures.


One of our paintings conservators has been looking at Stuart Davis pieces in our collection and it’s been wonderful since Davis seems to have utilized many cadmium-based pigments. VIL allows us to map the presence of cadmium pigments on the surface, as you can see in the images below of Pad No. 4. The areas that are not luminescing as strongly are likely paint mixtures.


It can even help to visualize brushstrokes (Stuart Davis. Famous Firsts)!


We have also been using this technique to look at our Egyptian mummy portraits as part of the APPEAR project. Our paintings conservator Lauren Bradley has been examining these pieces and we plan to share more of our findings with you all very soon!
Posted by Dawn Kriss and Anna Serotta