Multispectral imaging - Visible Induced Luminescence photography (VIL)
Analytical technique description:
The technique belonging to the multispectral photographic techniques. It is a non-invasive and portable method of analysis for objects of art. It useful for spatial resolution of some pigments. As ultraviolet fluorescence photography, visible radiation is sent on the surface of the object and in some cases an emission in a higher wavelength (near infrared range) occurs.
The images are acquired by means of a digital camera with the inner low-pass filter removed. To provide only visible radiation filters are insert ahead the flashes. The images obtained are in grey scale tones.
Spatial resolution of pigments such as Egyptian Blue, Han Blue and Han Purple on different type of surfaces.
The emission from flashes is filtered to obtain only visible radiation. The object should be irradiate homogenously. The physic theory is the same that occurs for ultraviolet fluorescence but in this case the emission happens in near infrared region.
The luminescence is centred around 910 nm. The period between absorption and emission can be extremely short and pigment appear as a bright spots. It an efficient method to characterize Egyptian Blue in a mixture or such as pure pigment.
Instrumental details:
Canon EOS 400D, Flash Quantum mod. T5D con filtri Schneider Optics B+W 486 UV/IR digital blocking, filtro Schneider Optics B+W 093 IR sull’obiettivo (Florence Unit).
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Institute for the Conservation and Valorization of Cultural Heritage