Conservator Kim Cullen Cobb uses photographs to compare aviator goggles in the National Air & Space Museum collection.
Technology and Training (NCPTT) grant MT-2210-10-NC-10, “Molecular characterization and technical study of historic aircraft windows and head gear using portable Raman spectroscopy.” The grant impetus was to evaluate a portable Raman spectrometer as a potential survey tool for rapid characterization of plastics in museum collections. This was explored through an applied case study of window materials used in aviation beginning in World War I. The Smithsonian’s National Air and Space Museum (NASM) and Museum Conservation Institute (MCI) collaborated in this endeavor.
Initially, a historic collection of aircraft windows was sought to test the portable Raman spectrometer with the assumption that transparent, colorless plastic sheets would be a relatively simple analytical problem. Plastics that were colored, opaque, and of varying thickness could be studied once the usefulness of Raman was established. As it turned out, the grant award coincided with NASMs collection move to its new Steven F. Udvar Hazy Center, and many aircraft of interest have not been accessible. NASM provided a collection of >80 aviator goggles and helmets for study in the interim. It was assumed that the lenses would meet the requirements of transparency and color. The headgear was examined for construction and condition, and lenses and other plastic elements were analyzed by Raman and X-ray fluorescence (XRF) spectroscopies to identify the materials.
Investigator Odile Madden uses the fiber optic probe of a portable Raman spectrometer to characterize the polymer interlayer of laminated glass lenses. (National Air & Space Museum Object A1976.1327.000)
The research goals of the grant have been met. Portable Raman spectroscopy has proven a useful tool for identification of synthetic polymers, plasticizers, and other compounds in plastic. It now is used routinely for sorting transparent and colorless plastics at MCI and often can identify major components of intentionally colored or degraded plastics too. We modified the spectrometer probe for analysis of laminated glass structures, a category of materials we had not anticipated when the grant was written. Using these tools, plus more sophisticated research Raman and XRF spectrometers at MCI, we have constructed a timeline for the development of historic window materials and aviator eyewear through the present day. The technological evolution of protective eyewear is much more rich and complex than anticipated. We are ready to continue our investigation of aircraft windows when access to aircraft from those periods becomes available. From archival research we have a good idea of how these materials evolved industrially and look forward to improving that with examples of aircraft in the NASM collection.