X-Ray Fluorescence (XRF - X-Ray Fluorescence) The fluorescence of X-rays (XRF) is a non-destructive technique, which has been often used in Archeometry to investigate the elementary composition of materials and pigments present in an artwork. In this case, it was used to characterize the pigments present in the analysed paintings. In the analysis of X-ray fluorescence the X-ray photons of an x-ray tube interact with the orbital electrons of an atom (of the material of the object under analysis), and these are taken from a more internal orbital, generating a vacancy. In this way, the photons take these electrons to more excited levels, while creating the vacancy, and in this transition they produce the X-ray which characterize of the elements present in the samples. Because it is a technique of element analysis, X-ray fluorescence cannot identify the chemical aspects of the compounds present in the sample, only its constitutive elements.
They allow us to record the real images of the painting with high quality. They have been captured with a digital camera with a CCD sensor of 10,7 Mega Pixels. The illumination was realized with continuous light, produced by two halogene lamps of 3.200 ºK of 1.000 W each, projected with an angle of approximately 45º on the painting.
Non-destructive optical technique in which the image is obtained by use of a digital camera with CCD sensor and IR filter, attached to the lense. In the measurements of spectrum IV, a constant source of light was used, with two halogene bundles of 3.200 ºK of 1.000 W each, also reaching the object at a 45º angle. A digital camera of high resolution was used to register the images, operating between the bands of the UV spectrum, visible light and IR, with waves varying from 380nm to 1.000nm. The images captured result of the combination of phenomena of reflection, absorption and transmission of the superficial layer, thus revealing the hidden peculiarities. The visualization of drawings depend on two aspects: contrast and transparency. Contrast is related to the material that has been used to produce the underlying drawing and to the reflectivity of the ground preparation. Transparency is related to the painterly layer and depends on the composition of pigments. If the medium used for the drawing is carbon-based, the absorption of spectrum IV is high and emphasizes the difference of the reflectivity and the ground preparation. In such case, the drawing becomes very visible, even when the painterly layer is very little transparent.
In this photographic technique, the fluorescence generated by UV radiation that strikes the painting is recorded. This UV radiation has the property of exciting the molecules of the substances present in the material. Consequently, there is the immediate emission of these radiations, which are distinct from the struck radiation. Phosphorescence can also occur in this process of excitation, but it is much slower that in fluorescence, and lasting some seconds or more. Fluorescence and phosporescence occur mainly in organic compounds, being very rare in inorganic ones. Therefore, they allow us to see superficial information of the painterly layer, while revealing funghi, tears, cracks and splits on polichromy and retouched areas. The differences between the original painting and the retouched areas are evidenced by UV fluorescence, because the retouches have been applied long after the painting was realized, and they bare different coloration, especially when applied over the lacquer coat. In UV measurements here realized, we used four bundles of UV light, Granilight, of 40 W each, and a fliter attached to the lense, in a dark room.
The radiographic exam, with digitized image, can help to evaluate the state of conservation of an artwork, as well as to reveal peculiar traits concerning the structure of the object, underlying elements or drawings, alterations and damages (repairs, cuts, etc), location of nails, and in some cases, the process of construction of the work
While trespassing the analysed material, the X-ray bundle suffers a process of atenuation, which occurs distinctively and is related to the energy of the incident bundle, composition, thickness and density of the material. The result is obtained through an image of grey hues due to the various factors of atenuation. In the case of an easel painting whose thicknesses are uniform, the darker parts observed can be a vestige of loss of polichromy (the X-ray bundle has a larger penetration). The lighter parts mean the presence of pigments with elements with high quantities of plumb atoms, such as white of plumb or gold (the bundle has difficulties in trespassing these areas). In some cases, radiography supplies information about the canvas itself (texture, etc).
In the analyses here undertaken, it was used a detector of type “Image Plate” . This is a bidimensional detector which has phophorus and is photostimulated by X-ray. The formed image of the irradiated object in the detector is captured in a special scanner that converts the image into digital signal, then directly transferred to the computer, so as to produce the digitized image.
See the images of the analyses undertaken of the work "L'Indovina" by Achille Funi.
In the upper part, from left to right, we have the images produced through the techniques of digitized radiography, infrared reflectography, and photograph of visible fluorescence with UV radiation. With the mouse, pull them into the image on the lower part, and the image obtained with visible light will appear.
In the field of applied sciences for the study of cultural heritage, non-destructive techniques in the analysis of painting are very broad and their object, quite varied. Interdisciplinary research has been contributing a lot in this area, by giving precise diagnoses, determining materials used by artists, period or stylistic school, as well as characterizing execution and creation techniques, revealing underlying drawings, showing conservation interventions and in the field of authentication. With the knowledge of the composition of materials and technology employed in the production of cultural heritage, it is possible to elaborate means and methods to better preserve cultural goods.
The scientific exams used in this work are classifed as non-destructive techniques, and/or surface exams, and they are based on procedures of the interaction of electromagnetic radiation with the painterly surface, including photographic techniques. They are: visible light, visible fluorescence with ultraviolet radiation (UV), and infrared reflectography (IR). By analysing each particular technique, one can obtain correlated information that allow one to characterize their study object.