Alexis North and Dr. Ioanna Kakoulli
Abstract
Digital analytical imaging utilizing the properties of visible (Vis), ultraviolet (UV), and infrared (IR) light has become a standard documentation and diagnostic tool used by conservators and art historians not only to create a record of an object’s appearance and condition, but also to uncover its method of manufacture, history, and previous conservation treatment. This non-invasive method has enabled the examination of a variety of objects of different geometry, complexity, and value providing useful information not discernible with the naked eye. Recent advancements in the medical and forensic imaging fields have led to the introduction in conservation of improved methods in the examination and documentation of objects of archaeological, historical, and artistic value.
This paper discusses the application of a forensic alternate light source (ALS) with tunable light capabilities for the analysis of objects under specific wavelengths of light and illumination conditions. Combining the tunability of the light source with longpass, shortpass, and bandwidth filters positioned in front of a modified DSLR camera in which the UV /IR blocking filter has been removed, an object is analyzed using reflectance and fluorescence imaging at the spectral range between 350 nm (ultraviolet-UV) and 1000 nm (near infrared-NIR). From the monochromatic images captured, false-color reconstructed trichromatic images including UV and IR false-color images can be obtained, enhancing specific features not easily discernible in the original black and white images, and assisting in the qualitative identification of certain materials.
The results obtained from this versatile approach show that augmenting analytical imaging with forensic technologies is an invaluable first step in the examination of objects, being an excellent tool for screening and prelim.inary characterization of materials. For example, reflectance in the UV and luminescence in the visible and NIR were performed on an ancient ceramic with a highly obscured surface, revealing long-lost decoration not visible in standard UV-induced visible fluorescence or NIR reflectance imaging. Issues of authenticity in a law enforcement setting were also resolved with the discovery and identification of traces of ancient paints based on their specific visible and infrared fluorescence emissions.