Since the 19th century, the development of scientific techniques for the conservation-restoration of works of art has enabled professionals to carry out in-depth analysis of the work and its stratigraphy. From microscopic examination to X-rays and simple observation under tangential light, essential data on the components of the pictorial material and its current state of conservation are gathered to help establish an accurate diagnosis. What’s more, the use of photography, in addition to magnifying the object with dedicated macro and microphotography equipment and functions, enables us to keep a record of the technological examination, and thus a material and visual trace of the various stages of restoration work carried out on a painting.
Some exemples...
... In the visible
BINOCULAR MAGNIFYING GLASSES
Magnifying glasses with a low amplification up to x3.5, they enable the professional to make an initial, magnified “naked-eye” observation of the artist’s workmanship, the components of the work (context of the canvas, thickness of the paint layer, etc.), alterations, etc. Based on this initial superficial examination, the need for more in-depth analyses and their targets will be decided.
TANGENTIAL LIGHT
Light directed laterally at an angle of 20° to 30° reveals the work’s surface condition and flatness defects, such as deformations, folds and raised material, as well as the extent and shape of the networks.
MACROPHOTOGRAPHY/PROXYPHOTOGRAPHY
Macrophotography is a photographic technique that allows the object photographed to be magnified by a factor of 1x to 10x, in natural or artificial light. It is used to focus attention on details that are almost imperceptible to the naked eye. It takes into account the surface condition of the paint layer and support, highlighting not only alterations and overpainting, but also the painter’s handwriting. Like all photographic techniques, it can be used to support the documentation of interventions and bear witness to the state of deterioration of the work prior to restoration.
Proxyphotography, or “close-up”, allows magnification factors ranging from 0.1x to 1x. Today, it is commonly associated with macrophotography, which is defined as the simple enlargement of the photographed image in relation to the actual size of the object, remaining “visible to the naked eye”, unlike microphotography, which opens up the “invisible”.
...In the invisible
ULTRA-VIOLET LIGHT
Paint materials fluoresce differently under ultraviolet light, depending on the nature of their components and their age. This examination makes it possible to discern the presence of one or more varnishes and their surface unevenness, as well as any overpainting, thus revealing past alterations and restoration work.
To be discernible under UV rays, overpaints – layers of paint applied after the painting’s creation – must have been applied at a later date than the present, and within a period of less than 150 years. In this case, they emit a different fluorescence from that of the original colored layer, due to their two distinct temporalities and the time lag in the aging of their materials, and appear as dark opaque spots. If repaints are too old, and closer to the work’s creation date than to the present day, they will visually present an identical state of degradation and therefore a similar fluorescence under this light.
MICROPHOTOGRAPHY
This photographic technique, combined with observation of the image under a microscope, enables the object to be magnified by a factor of more than 10x, up to 1000x or even 40000x. It enables the analysis of elements imperceptible to the naked eye, and can provide important information on the components of the work, even at its lowest magnification. To enable this documentation, a videomicroscope can be used, or a camera combined with an optical micro-cutter, for a magnification factor ranging from 60x to 200x.
Tests de sensibilité...
…DES FIBRES DE LA TOILE A L’HUMIDITE ET AUX FORCES DE TRACTION
La sensibilité de la toile aux variations hygrométriques et aux contraintes physiques est inhérente non seulement à son tissage et sa contexture, mais aussi et à fortiori à sa nature. Déterminer celle-ci est indispensable à la bonne compréhension de l’évolution du support et de sa dégradation et ainsi de ses conséquences sur la couche picturale. Cette information entre aussi en considération dans le choix des matériaux à utiliser lors des interventions de conservation notamment en ce qui concerne les adhésifs. La cellulose est le principal agent responsable du vieillissement du support végétal et sa teneur dépend de la nature des fibres : le coton est, par exemple, le matériau au taux de cellulose le plus concentré après le bois (pour les supports à peindre) et de fait le plus fragile aux conditions climatiques, là où le lin présente une meilleure résistance générale aux variations hygrométriques et aux contraintes mécaniques, tout en restant sujet à dégradation.
Les résultats obtenus peuvent être comparés aux données connues sur l’utilisation des matériaux de la peinture à travers les siècles.
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