AIC's 52nd Annual Meeting

The Harvard College Observatory (HCO), founded in 1839, today has a collection of 550,000 astronomical glass plate photographs. For over a century, the astronomical photographic glass plates functioned as scientific records and living documents that were often handled by multiple researchers who left various annotations directly on the glass plates in colored inks. The glass plates are known to have been cleaned of markings and re-used for different research purposes at different times. Many of the ink annotations were made by the often-uncredited Women Computers and Astronomers who worked at the HCO in the late 19th and early 20th centuries. Unfortunately, these important annotations on the plates obscured astronomical data. The talk focuses on the analysis of the inks, developing a protocol to image the plates to digitally omit the annotations yet still preserve the astronomical data, and the pivoting of the collections point of view towards holistic artifactual preservation.

Starting in 2004, the HCO’s Digital Access to a Sky Century @ Harvard (DASCH) project endeavored to digitize the astronomical data in the majority of the Observatory’s glass plate negatives to produce full photometry results for the entire sky. As a matter of procedure, plates selected for DASCH were first photographed and then cleaned of their historical annotations before digitization.

The Williamina Fleming Collection at Wolbach Library comprises 679 individually selected astronomical glass plate photographs with historic annotations still intact which represent the discoveries, research, and working process of the Women Computers. The collection is named in honor of Williamina Fleming (b.1857 - d.1911), the first Curator of Astronomical Photographs at HCO.

During the Covid-19 pandemic, HCO shifted priorities away from the digitization of purely the scientific information in the collection to embrace a more holistic preservation of the photographs considering the historic and cultural values of the plates too. This began a multi-year collaboration at Harvard University to address the preservation needs of the Williamina Fleming Collection.

A technical study of the inks used for the annotations was undertaken using reflection FTIR, microfading tests, and multispectral imaging. The reflection FTIR was used to noninvasively probe the chemical composition of the inks. The microfading test on the inks showed that they were somewhat photosensitive. These results provided guidance for the development of exhibition guidelines for the plates.

When multispectral imaging was conducted at the Weissman Preservation Center using a Video Spectral Comparator (VSC 8000) in 2022, it was found that the green, red, purple, and brown ink annotations on the plates were rendered transparent in transmissive IR at 850 nm. This showed a possible way forward for digitizing the scientific information without removing the historic annotations on the glass plates. In 2023, the Harvard Plate Stacks undertook more intensive exploration of multispectral imaging of glass plate negatives with R. B. Toth Associates, using a monochromatic 150 megapixel PhaseOne camera.