CHI Blog Post—May 2010
By Guest Blogger E. Keats Webb
Senior Conservator, Melvin Wachowiak, and I have continued using Reflectance Transformation Imaging (RTI) on a regular basis at Smithsonian’s Museum Conservation Institute aiding in the research and preservation of the collections both within the Smithsonian and outside. We have found the technique to be a great indicator of the condition of objects as seen in the imaging of a 2×2.5” daguerreotype. A daguerreotype is one of the earliest photographic processes that formed an image on a silver coated copper plate. The highly reflective and relatively flat surface proved to be an ideal candidate for the RTI process. Using a 21-megapixel full-frame sensor, our final RTI file revealed the detailed information of polish marks and scratches on the metal surface and allowed very close examination due to the high resolution.
The image acquisition for the RTI process has definitely been an adventure of trial and error. When initially imaging the daguerreotype, we ran into issues with flare on the object. We crafted a homemade snoot from cardstock, black velvet and rubber bands, which quickly solved the problem and generated a beautiful final RTI file. This was not our first run-in with stray light. Working with larger objects on the wall and even smaller objects on the copy stand, we have experienced stray light from surroundings including the floor and ceiling tiles and the copy stand post, issues that we remedied with available non-reflective diffuse material like dark moving blankets or scrap velvet. A final example of our adventures of image acquisition includes a human skull and a ring flash. We were losing information to shadows in the roof of the mouth of a skull while imaging the gold filings in the teeth. To resolve this loss of information we used a (stationary) ring flash during the image acquisition in addition to the standard repositioned light source. Before processing the files in RTI Builder, we batch-edited the files removing the ring flash highlight on the reference spheres, which produced a successful final RTI file.
In our image acquisition explorations, we have adopted a creative process of trial and error to our RTI workflow that can incorporate crafting homemade devices and using available materials to remedy unexpected hurdles.
I really enjoy the opportunity to attend conferences and particularly the Computer Applications in Archaeology conference, which was in Granada Spain this year. It is a great opportunity to catch up with colleagues and friends, share experiences and get advice. This year was also an opportunity to sit down with our collaborators at Southampton University, Graeme Earl and team at the Archaeological Computing Research Group.
Graeme’s team recently won a significant UK grant to work with RTI technology and we are collaborating on the project. The team there has graciously allowed us to influence some of their priorities for enhancements to the RTI software as part of the grant work. We are still discussing some of the ideas, and it’s great fun to work with a group with such enthusiasm and desire to keep things moving forward for the growing community of RTI adopters.
I look forward to great things from this collaboration as it continues.