Sibilla
1619-1620
state of conservation
state of conservation
The examination methods used to ascertain the state of preservation and to verify the existence and extent of non-original parts of the pictorial fabric include the photographic technique in grazing light (RAD) and UV-induced visible fluorescence (UVF) technique.
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.
The photographic technique of ultraviolet radiation-induced visible fluorescence (UVF) exploits the behavior that some materials have when illuminated by a light source emitting ultraviolet radiation not visible to the human eye: ultraviolet light is absorbed into the surface and visible light is re-emitted. The different brightnesses, or fluorescences, observable on an irradiated painting depend not only on the chemical composition of the substances in the coating varnish and pictorial layers, but also vary over time. This is the reason why fluorescence photography is effective in distinguishing repainting from original drafting: more recent and overlapping materials tend to appear darker due to the different color and intensity of fluorescence they show, so parts that have undergone recent restorations or additions will appear darker or totally black.
