Technical Photography (TP) represents a collection of images realized with a modified digital camera sensitive to the spectral range about 360-1000 nm.. Different lighting sources and filters are used to acquire a selection of technical images, each one providing different information regarding the object under examination.
A Technical Photography documentation consists of a collection of scientific images realized with a modified digital camera sensitive to the spectral range about 360-1000 nm. Each image provides just a bit of information but all together they represent the most practical and successful methodology to study art and archaeology.
Art examination starts with a high-quality photographic documentation in the standard visible range of the electromagnetic spectrum. Color camera calibration, exposure correction, white balance, sharpness. color checkers, resolution. These are some of the topics to master in order to obtain quality photo documentation of art objects and archaeology. Polarized light photography (PL) and Raking light photography (RAK) are very helpful photographic methods widely used by fine arts photographers and they also belong to the visible range of the spectrum.
Raking light photography (RAK) is a very simple method. Nevertheless, it allows to reveal and to document numerous information. A standard VIS photo is intended to reproduce the look of the artwork as seen in museum lighting, with soft and diffused light. RAK photo clearly shows how the paint was laid (brushwork), texture and building up of figures and details.
Ultraviolet Fluorescence photography (UVF)
Some Art and conservation materials (pigments, binders, varnishes, consolidants, adhesive…) exhibit the emission of visible light of different colors when they are exposed to ultraviolet radiation. This phenomenon – called ultraviolet fluorescence – can be appropriately documented using proper filters and UV lamps and it provides plenty of information on the presence and distribution of these materials. Among the technical photographic methods, UVF is the most widely used for many kinds of artifacts; paintings, textiles, paper, historical documents, stone, even photography conservation.
Ultraviolet Fluorescence photography (UVF) is probably the most diffused technical method for art examination since it can be successfully applied on practically every art or archaeology object category. In a painting, UVF photo reveals retouchings as dark spots while the aged original materials exhibit light emission with different colors.
Reflected Ultraviolet photography (UVR)
The main application of this methods is to identify and map modern white pigments (zinc white and titanium white) which absorb UV radiation and appear dark in UVR photography. On the other hand, the historical lead white pigment is a very good UV reflector and shows up very bright in UVR images. Lead white was used from antiquity to the 1920′ when the modern and safe titanium white totally replaced it. UVR photography is a very effective method to tell the presence of inpaints made with modern white over original lead white.
The main application of this methods is to identify and map modern white pigments (zinc white and titanium white) which absorb UV radiation and appear dark in UVR photography. On the other hand, the historical lead white pigment is a very good UV reflector and shows up very bright in UVR images.
Infrared photography (IR)
Some pigments become transparent in the near infrared and infrared photography can reveal underdrawing and changes. in particular ochre pigments (yellow ochre, red ochre, raw sienna…) and red and yellow lakes are the ones that become more transparent totally revealing traces of hidden drawing.
Infrared photography can reveal underdrawing, changes and even faded signs, as in this example. Some pigments become transparent already in the near infrared range that a modified digital camera can detect. The dark pigments in this example disappear in the IR image revealing the white support and the sign which was written with a carbon-containing paint which remains opaque in IR.
Infrared False Color photography (IRFC)
Infrared False Color photography (IRFC) is used to map inpaints and to tentatively identify pigments or at least distinguish original paints from inpaints. Even if the original pigments and the modern ones used for the conservation treatment have the same visible color and cannot be distinguished by the naked eye, IRFC photography can reveal the new paints if they reflect or absorb infrared differently than the original ones.
Infrared False Color photography (IRFC) reveals inpaints making easy to distinguish original paints from later additions. Original pigments and the modern ones used for the conservation treatment have the same color and cannot be distinguished by naked eye. On the other hand, the original paint absorbs infrared while the modern one reflects it, thus the different infrared false colors.
Some molecules and minerals (among them mineral pigments) exhibit Infrared Fluorescence. This phenomenon is similar to Ultraviolet Fluorescence where a beam of ultraviolet light produces visible light emission. In the case of infrared fluorescence, a beam of visible light generates an emission of infrared radiation. IRF photography allows to map and detect Egyptian blue and cadmium-based pigments.
Infrared Fluorescence photography (IRF) makes retouches with cadmium-based pigments to stand out as bright spots. In this example, the vermilion used for the red drapery of this oil painting was retouched with modern cadmium red which appears bright in the IRF image.
Transmitted Infrared photography (IRT) allows to detect underdrawing and pentimenti. It is a very effective since pigments become even more transparent than in the usual IR photography method. IRT can be applied only for art objects on translucent supports, such as paintings on canvas, drawings on paper, historical documents and manuscripts.
Transmitted Infrared photography (IRT) could results even more successful than standard IR photography in revealing the underdrawing and the building up of the figures. This example shows how the exact sequence how the paint layers were laid on. Notice the red drapery was added on a naked right arm already sketched.