The wonderful e-conservation Magazine is now a Journal, and I’m honored that their first number hosts a paper of mine where I discuss some macro photographic methods for RTI, Reflectance Transformation Imaging, to document sub-millimeter surface details on works of art:
A. Cosentino “Macro Photography for Reflectance Transformation Imaging: A Practical Guide to the Highlights Method” e-conservation Journal 1, 2013, pp. 70–85.
I add here a video showing the RTI image of the 10 euro bill discussed in the paper.
Reflectance Transformation Imaging (RTI) is definitely widely used for art documentation and analysis, even for the examination of features on the order of hundreds of microns. In this paper I show some macro scale photography methods for macro RTI employing the Highlights method which consists in including one reflective sphere in the scene photographed. It is up to the RTI processing software to calculate for each photo the direction of the light using its reflection on the sphere. To showcase this method on works of art and historical prints I am thankful to the Ingels Collection which allowed me to public the RTI images of prints ranging from the XV to the XX century. Macro RTI is useful to determine the printing technique: woodcuts, etching, engraving and blockprints.