Fiber optic probes allow for in situ characterization of cultural heritage objects and analysis of materials that are difficult to access. Positioning these probes is challenging in terms of focal distance, angle of analysis, and stability. Modifications to improve control include stabilizing the probe against a stationary surface, typically mediated by a tripod, or against the artifact itself with a distance regulating sheath that fixes the focal point at the object surface. The first makes the system less portable, while the second eliminates depth profiling capability. An adjustable working distance adapter was created that allows the operator to position a fiber optic probe against the surface of a transparent artifact and move the working distance up to 6 mm into the material while excluding ambient light. The hollow adapter contains no optical fiber, lenses, or windows, so optics are dictated by the fiber optic probe. The tool was created to study the polymeric interlayers in laminated safety glass used in early 20th century aviation and also could be applied to contemporary laminated glass, other multilayer transparent objects, and substances in transparent containers. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.

A novel, non‐invasive study of goggles, flight helmets, airplane windows, and canopies in Smithsonian collections is the first known large‐scale technical survey of historic aviation plastics and leverages the world's largest air and space collection as evidence of the materials and technologies used to create transparent plastic objects in the early‐20th century. Transparent windows in these artifacts were analyzed with Fourier transform and portable dispersive Raman spectrometers to identify polymers and plasticizers present. The study demonstrates the potential of Raman spectroscopy to objectively and non‐destructively measure historic plastic compositions, including formulations that have become obsolete. Data was interpreted in combination with archival research of historical documents to identify window materials including glass, laminated safety glass, and sheets of plasticized cellulose nitrate, plasticized cellulose acetate, and poly(methyl methacrylate). Results are contextualized into a coherent history of the role transparent plastics played in enclosing airplane cockpits. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.

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