Multispectral imaging - Ultraviolet fluorescence photography (UV)
Analytical technique description:
The technique belonging to the multispectral photographic techniques, called imaging. It is a non-invasive and portable method of analysis for objects of art. It could be used for spatial identification of varnish and protective, but also binders and repaintings. Furthermore some pigments possess characteristic fluorescence, useful to differentiate them from others.
Applications:
Organics materials on every surface such as fresco, canvas, marble and wood.
Basics:
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. In this case, the emitted light has a longer wavelength and therefore lower energy, than the absorbed radiation. The emission happens in a short period of time.
The ultraviolet fluorescence occurs when the absorbed radiation is in the ultraviolet region of the spectrum, and thus invisible to the human eye, and the emitted light is in the visible region. This fluorescence can be acquired from a camera equipped with a filter to cut ultraviolet and infrared reflection from the surface and environment.
Furthermore the emission increase with ageing, due to intensification of chemical interactions, and this property could be worthwhile to distinguish latest repainting.
Instrumental details:
Canon EOS 400D, Flash Quantum mod. T5D with Schneider Optics B+W 403 UV passband filter and Schneider Optics B+W 486 UV/IR digital blocking filter for lens (Florence Unit).
ICVBC - AREA DI RICERCA CNR DI FIRENZE
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Institute for the Conservation and Valorization of Cultural Heritage