The electromagnetic radiation that our eye can detect falls within a range of wavelengths, (“visible light”), from about 400 to 750 nanometers. Beyond these limits, the radiation becomes invisible to humans, but it still can interact in various ways with matter, e.g., through absorption, reflection, transmission, similar to what happens with visible light.

Infrared reflectography is an image acquisition technique that exploits the ability of infrared radiation (wavelength of near-infrared radiation 800-1000 nanometres) to penetrate below the surface of paint and visualize compositional paint changes. By taking advantage of this property, it is possible to observe – where present- preparatory  sketches underneath the pictorial layer or to reveal pentimentos (afterthoughts, regrets) or to study changes made by the artist. The images that can be obtained are greyscale, where the lightest areas are those with chemical-physical characteristics that reflect infrared radiation either to a larger extent or completely. The sensitivity of the analysis depends not only on the chemical nature of the paint layers but also on their thickness. Infrared reflectography is pivotal in order to study the painter’s technique and the ‘idea’ at the origin of the painting: it is possible to observe elements that are not visible to the naked eye and to provide information on the evolution of the composition and construction methods of the artwork.

The modus operandi of Barbieri is mainly based on a direct drafting of color, almost abandoning the technique of preparatory drawing, limiting itself to short strokes, thin, not continuous and half dry for the realization of the contours of the face and half fluid for the folds of the dress.

A fluid medium brush is, instead, used by Guercino in some steps, to create an artifice aimed at «detaching from the bottom» certain elements, in order to bring them into the foreground, in a sort of three-dimensional treatment. This is visible in the hand holding the scroll.