REFLECTANCE TRANSFORMATION IMAGING OF TRANSPARENT POLYMERS
BY ALEXANDER M. DITTUS
Reflectance Transformation Imaging (RTI) is a method of computational photography that provides the conservator with an easy and inexpensive means to generate virtually controllable raking light photographs. The data is acquired from the surface reflection using a camera, a reflecting sphere, and a light source. To this date, using RTI for transparent materials like PMMA, PS, PE, PET and many others was considered impossible. However, it can be proven that generating RTI files from such materials is not only possible, but creates results that help to investigate and visualize multiple traces of an object’s manufacturing process, as well as phenomena of aging and use. Thus, it is possible to document these features that are often hard to display using regular photography. Pictures created from RTI files can be used in conservation reports and publications to visualize surface structures as well as phenomena underneath the material’s surface. Furthermore, the digital raking light files created with this technique can be saved in databases or online resources for researchers to address an object depending on their research interests. Besides the interactive variation of the light, there is also the chance to enhance details of the object’s optical surfaces using various filters. This enhancement helps to show casting seams, bubbles, scratches, cracks, and many other features that would remain invisible or hard to distinguish from the surrounding material in a traditional photo. The technique will be explained and an easy way to create RTI files from transparent polymers will be introduced. Short introduction into the broad range of applications for the investigation of plastics will be given, using various examples and the field of applications will be widened even further by the introduction of Micro-RTI for transparent objects. While there are well established standards for traditional documentation methods, like photography, in science and conservation, the need for such a new standard arises when a new method like RTI gains ground. Thus, a suggestion for a common standard for displaying RTI images will be made.