UV fluorescence photography
V photography is used to examine works of art in a non-destructive manner. When analyzing the condition of the painting ultra violet (UV) fluorescence photography is used to determine prior restorations, authenticity of signatures, presence of a varnish or even number of layers of varnish. It also helps to identify materials used by the artist.
UV fluorescence photography involves irradiation of an object with UV light while measuring the emitted fluorescent light only in the visible range. UV radiation penetrates only the surface layer of the art object and can therefore provide extensive information regarding the varnish layers. Once an object is irradiated with long or short UV rays, a normal camera can be used with a barrier filter, to capture different shades of UV fluorescence. Since organic and inorganic matter absorbs and reflects UV light to different degrees, the recording of reflected UV light can help identify substances in the surface layer. For example, certain white pigments can be detected and differentiated by their UV fluorescence which aids with dating of a painting and deciding upon which material to use for restoration.
Infrared radiation is situated within the electromagnetic spectrum just past the red segment of visible light. Unlike visible light, infrared radiation penetrates somewhat deeper into the layers of a painting, depending upon the pigments, varnishes and other materials used during its execution.
Infrared photography allows us to see what lies behind the paint layer in a non-destructive manner, bringing to light underdrawings, grids or perspective lines, pentimenti (artist’s changes to the original composition), the depth of the craquelure, prior restoration interventions and also signatures, dates, inscriptions or monograms hidden underneath the painted surface layer.
It is the most suitable method for the visualization of the current condition of the work of art. When the restoration is carried out, the infrared image is often used together with the X-ray image of the painting in order to compare the current state of the work of art with the one that was originally intended. The infrared image is also used when studying the artist’s painting technique – the stress put on the pencil, the direction of the stroke, and the choice of his drawing materials – chalk, charcoal, red chalk, pencil, etc. -, making it an absolutely vital tool in verifying the authenticity of a work of art.