Multi IR reflectography

Optical techniques are widely disseminated in the field of painting diagnostics because of their effectiveness and safety. Among them, infrared reflectography is traditionally employed in painting diagnostics to reveal features underlying the pictorial layer thanks to the paint layer transparency to NIR radiation. Highresolution reflectography was introduced in the 1990s at the Istituto Nazionale di Ottica Applicata, where a prototype of an innovative scanner was developed, working in the 900-1700 nm spectral range. This technique was recently improved with the simultaneous acquisition of the reflectogram and the color image, perfectly superimposed. Here we present a scanning device for multi-spectral IR reflectography, based on contact-less and single-point measurement of the reflectance of painted surfaces. The back-scattered radiation is focused on square-shaped fiber bundle that carries the light to an array of 14 photodiodes equipped with pass-band filters so to cover the NIR spectral range from 800 to 2500 nm.