I was excited to see the most recent update on VIL imaging as it is an accessible imaging technique that can be used to localize pigments with specific characteristics. It is useful for anyone interested in painted surfaces, and can be used in conjunction with other multispectral imaging, or as a standalone technique.
The basic idea is that you need a light source to produce visible light, a camera with its infrared filter removed, and a bandpass filter to limit the type of light that gets to the camera sensor, along with some standards to help process the images. The pigment particles on the object are excited in the visible range, and emit infrared radiation which is detected by the modified camera. This technique can be used to detect trace remains of pigments that are all but undetectable to the naked eye. The technique was developed by scientists from the British Museum and the Courtauld Institute (see Verri et al., 2009) .
In the case studies shown in Dawn and Anna’s presentation the focus was on Egyptian blue, which produces luminescence in the infrared (~910nm) when exposed to visible light. Optimizing the capture and processing protocols will mean better results and hopefully, a means of standardizing and sharing information between conservators working in different labs. While VIL is gaining popularity as more museums add it to their workflow (for example. as part of the APPEAR project spearheaded by the Getty), the technique is still being developed, with much more progress on the horizon. Dawn and Anna reported on results of a survey of VIL users to show where progress has been made and where we can still expect some improvements in the technique.
While its initial development as a tool for identifying Egyptian blue has led to its popularity among archaeological conservators, it seems like the technique is ripe for more widespread adoption for research into modern pigments, some of which also have unique luminescence properties.
Conservators can use a variety of wavelengths using targeted or tunable light sources (e.g. the CrimeScope, adapted from the forensics field) to survey visible-induced luminescent pigments (other examples of which include dragon’s blood, Indian yellow, Han blue, cadmium red and yellow). Dawn and Anna showed an example of imaging surveying cadmium pigments used in Stuart Davis’s Mellow Pad carried out by their Brooklyn colleague Jessica Ford. For more on the work from the team at the Brooklyn Museum, see their recent blog post here.