“Seeing the Unseen”

Tests on some of the Museum’s gratings have been carried out at the Canadian Conservation Institute. (Courtesy CCI)

The really interesting thing about spectroscopic gratings is that their makers never actually saw the details of the rulings they were making. The fine lines are actually below the resolving power of all optical microscopes. The makers could only improve their machines and techniques by carefully observing the spectra, assessing flaws like poor focus, faintness and ghost images (faint duplicate but displaced lines). It was not until the 1960s that anyone tried to “see” the surface of a grating with an electron microscope. It wasn’t a scientific initiative, however, but a study undertaken by two historians wanting to learn more about Nobert’s remarkable test plates. At the Canada Science and Technology Museum, this type of study has been taken further. Several of the spectroscopic gratings in the Museum’s collection have been viewed with scanning electron microscopes (SEM) at the Canadian Conservation Institute (CCI). The electron micrographs were made at 2000X to 10000X magnification and at 20000 kV. They reveal some interesting details, which can be seen here. The first two gratings are not in the Museum’s collection, but have been included to show how spectrographic gratings have improved over time.

Conservation 

CSTMC’s Conservation Laboratory

Upon acquisition by the museum, all artifacts are carefully examined by the Conservation Division. This examination leads to the production of a “Condition Report” in which the artifact is described in detail. Special attention is given to materials, finish and methods of construction. In addition, functionality (in so far as it can be tested), damage, corrosion, stains and signs of wear are always carefully noted. Photographs are taken as documentation. These careful observations by trained conservation professionals thus provide the rationale for any treatment required. This treatment is defined, step by step, and the resulting “Treatment Proposal” is passed to the Curator responsible whose approval is required before work on the artifact may begin.