When a light wave with a single frequency strikes an object, a number of things could happen. The light wave could be absorbed by the object, in which case its energy is converted to heat. The light wave could be reflected by the object. And the light wave could be transmitted by the object. Rarely however does just a single frequency of light strike an object. While it does happen, it is more usual that visible light of many frequencies or even all frequencies is incident towards the surface of objects. When this occurs, objects have a tendency to selectively absorb, reflect or transmit light certain frequencies. That is, one object might reflect green light while absorbing all other frequencies of visible light. Another object might selectively transmit blue light while absorbing all other frequencies of visible light. The manner in which visible light interacts with an object is dependent upon the frequency of the light and the nature of the atoms of the object.
• Researchers and mainly those involved in the science of conservation and art history employ an amalgamation of examination and imaging techniques to explore the multiple layers of a painting, layers that are both visible and invisible to the naked eye. Some of these approaches require the simple use of unusual lighting angles, while others involve very specialized equipment capable of producing or capturing electromagnetic wavelengths above or below the narrow band of the visible spectrum. While one technique may assess the nature and condition of the varnish, pictorial and restoration layers lying on the surface, others are capable of recording hidden layers lying below the visible image.
• The techniques that we have employ to the painting are used as a preliminary identification of the spatial layered morphology and the characterization of the pigments and varnishes used, the results have been assessed and used at the second stage of the methodology; the physicochemical analysis. The selected wavelength of the acquisition spans from 365 nm to 1100 nm at selected visible (VIS), infrared (IR) and ultraviolet bands (UV). The objective of the analysis is the overall characterization of the painting.
• The applied methods are visible large format visible photography (LF VIS) , large format photo-macrography (PHM), spectrum photography or multispectral imaging (MSI) that incorporates a wide gamut of imaging, and spectral reflectance transformation imaging (RTI) (IRRTI) a unique method of mapping interactive light on digital surfaces.
• The methodologies employed are non-destructive ways of examination and are based on standardized methodologies and recommendations based on the American Institute for Conservation of Historic and Artistic Works (AIC). All equipment and techniques used for the acquisition of digital imagery are recommendations of the council in order to avoid damage of materials due to radiation exposure to the painting on the ultraviolet and infrared bandwidths. Sampling on important works of art is not possible and this is the main reason why only non-invasive techniques, such as MSI, are becoming increasingly popular to assist with undertaking conservation decisions.
• The digital content acquired is properly documented. The digital life span of the imagery is recorded for the purposes of of enhancing long-term availability to research and beyond, transparent access and interoperability, monitoring (tracking changes), digital preservation and security. The intrinsic and extrinsic camera properties and lighting equipment used are recorded in order to provide scientific reliability of the content. The protocol that is used is the IPTC. The IPTC Photo Metadata standard is the most widely used standard because of its universal acceptance among photographers, distributors, news organizations, archivists, and developers. The schema defines metadata structure, properties, and fields, so that images are optimally described and easily accessed later.
Near Infrared Spectrum
- Infrared (IR) (700nm, 830nm)
- Infrared Transmitted (IRT)
- Infrared False Color
- Infrared Fluorescence (Identification of Egyptian Blue and Cadmium Red and Yellow pigments)
- Large Format IR (LF-IR)
- Infrared Raking Light (IR-RAK)
- Infrared Reflectance Transformation Imaging (IR-RTI)
Ultraviolet Spectrum (UV-A)
- Ultraviolet Fluorescence (UVF VIS spectrum)
- Ultraviolet Reflectance (UVR 365nm,400nm)
- Ultraviolet Reflectance Transformation Imaging (UVR-RTI)