I noticed I often talked about Infrared Fluorescence Photography in my posts, such as the one on historical pigments, and the one on the Windsor & Newton Gouache color chart, but I didn’t properly introduced the technique yet. This post want to be a brief review of the Infrared Fluorescence Photography.
Some molecules and minerals (among them mineral pigments) exhibit Infrared Fluorescence. This phenomenon it’s similar to Ultraviolet Fluorescence where a beam of ultraviolet light produces visible light emission. In the case of Infrared Fluorescence, a beam of Visible light generates an emission of Infrared light.
Infrared Fluorescence is observed in few rare minerals  but also in a very common molecule, Chlorophyll!Its use in Technical Art examination
Among historical pigments Egyptian blue, cadmium red and cadmium yellow are the ones exhibiting infrared fluorescence. As the name says Egyptian blue is the blue actually used by the Egyptians and Romans. So, infrared fluorescence photography it’s used in archaeology  to detect even tiny fragments of Egyptian blue pigment. The first publication on its application to art and specifically to identify cadmium-based pigments goes back to the 1963 . As reported in [4, 5] the Infrared fluorescence emission of cadmium pigments is centered at about 850 nm. Finally, a valid source of information on a wider range of minerals is .
Infrared Fluorescent Brush!
This was really puzzling me for a while. I was pretty happy when eventually I found out what was wrong. Well, I was seeing infrared fluorescence from pigments that were not supposed to be IR fluorescent. It was the brush! I didn’t identify what the material is but I encourage you to check your brush for IR fluorescent material before using it to paint your swatches.
Experimental Set up
 G. Accorsi, G. Verri, M. Bolognesi, N. Armaroli, C. Clementi, C. Miliani, A. Romani “The exceptional near-infrared luminescence properties of cuprorivaite (Egyptian blue)” Chem. Commun., 2009, 3392–3394.
 C. F. Bridgman and H. L. Gibson “Infrared Luminescence in the Photographic Examination of Paintings and Other Art Objects” Studies in Conservation, Vol. 8, No. 3 (Aug., 1963), pp. 77–83.
 A. Casini, F. Lotti, M. Picollo, L. Stefani, A. Aldrovandi “Fourier transform interferometric imaging spectrometry: a new tool for the study of reflectance and fluorescence of polychrome surfaces” Conservation Science 2002, Non Destructive Tests, 248–252.
 M. Thoury, J. K. Delaney, E. R. De la Rie, M. Palmer, K. Morales, J. Krueger “Near-Infrared Luminescence of Cadmium Pigments:In Situ Identiﬁcation and Mapping in Paintings” Applied Spectroscopy, Volume 65, Number 8, 939–951, 2011.
 D. F. Barnes “Infrared Luminescence of minerals” Geological Survey Bulletin 1052-C, United States Goverment Printing office, Washington, 1958.