Infrared Fluorescence Photography: Review

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 introduce the technique yet. This post wants to be a brief review of the Infrared Fluorescence Photography.

Infrared Fluorescence

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.

 

Ultraviolet and Infrared Fluorescence can be both described as a phenomenon where a specific light is an input and another longer wavelength light is output.

Infrared Fluorescence is observed in few rare minerals [1] but also in a very common molecule, Chlorophyll!

Chlorophyll emits infrared fluorescence in the very near infrared. Indeed, its fluorescence is brighter in the IRF 850 image – where the 850 nm filter was used, allowing through the closest infrared. Notice that, on the other hand, the infrared fluorescence emission of the cadmium red swatch is almost unchanged since it happens at a longer wavelength (over  850 nm [4, 5]).It’s used 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 [2] 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 1963 [3]. 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 [6].

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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

As the input, we need a source of Visible only-light and I post about it here. As IR filter for the camera lens: Heliopan RG1000. Exposure time is long, around 30″.

References

[1] http://www.viewsfromscience.com/documents/webpages/led_fluorescence_p2.html

[2] 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.

[3] 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.

[4] 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.

[5] 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.

[6] D. F. Barnes “Infrared Luminescence of minerals” Geological Survey Bulletin 1052-C, United States Goverment Printing office, Washington, 1958.

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