AIC's 52nd Annual Meeting

Reflectance Transformation Imaging (RTI) has been well established as a useful tool to study cultural heritage objects. Published studies vary widely vis-a-vis media focus, ranging from paper-based works, to archaeological stone, polished metal and more. Glass, due to its specular surface and transparency, presents particular challenges to this technology. Cooper Hewitt Smithsonian Design Museum (CHSDM) has embarked on an extended research project focused on recording cold worked glass surfaces using micro-RTI, in order to determine the most successful way to image this media through this technique as well as to investigate the surface morphologies and tool marks created through physical and chemical working methods. RTI capture strategies have varied from digital microscopy to a high-quality macroscopic camera lens. As research progressed, we received support to facilitate the creation of a bespoke four-way illuminated RTI dome featuring UV, IR, blue and white light LEDs.

This paper focuses on unexpected outcomes, learnings, and lessons gleaned along the journey into this research topic. Glass studied included 18th Century Dutch wheel cut vessels and diamond stippled glass, and 20th Century acid-etched French glass. Wheel-cutting of glass surfaces traditionally relies on an abrasive oil slurry applied to copper wheels, which rotate as they cut into the surfaces. The technique flourished by the mid 17th Century and later in the Netherlands. Similarly, diamond tipped engraving, often executed by female artists, found favor throughout the same period while diamond stippling reached a pinnacle in the 18th Century. The cut and stippled forms on these cups, goblets and vessels create sculptural and even ghostly images that contrast with the light reflected from untouched surfaces.

In contrast, acid etching relies on hydrofluoric acid to cut into the glass surface rather than a mechanical tool or physical force. The technique comes into commercial use by the latter half of the 19th century. French glass firms such as Daum Freres took advantage of this technology to create frosted surface effects, while artists such as Maurice Marinot exploited the acid to create deep recesses and intricate surface textures. Samples prepared specifically for this study to complement the museum collections included both acid-etched flash glass as well as diamond engraved surfaces. Our talk will present strategies for successful RTI capture on reflective, water-white transparent glass using the methods discussed above, as well as deeply etched glass objects. We also investigated imaging cast proxies for challenging or awkward shaped pieces. Finally, we will discuss what we have learned about surface changes to the glass following varying working methods.

The Hanson Rare Book and Baldwin Library of Historical Children’s Literature Collections at the University of Florida contain hundreds of pop-up and movable books. These books span the breadth of paper engineering—from the earliest Lull volvelle to the intense Reinhart Disney pop-ups of today. Their contents contain the history of paper engineering: how they evolved through various publishing houses, adopted technologies from other industries, and propagated around the globe to become one of the most engaging and increasingly popular book forms of today, and yet many are actively falling apart.

Upon review of several of these engineering marvels, I found that the damage is not due to typical readership wear, but rather due to people’s innate curiosity in how these mechanisms are made and function. Given the task to repair and maintain them for long-term use, I realized that a methodology that catered to the curious maker—giving those who are interested greater access to the engineering structures within these books—could preserve these items for longer. I also wanted to make these engineering structures more accessible for those who could not come to our reading room and spend time with the books in our collections (digital scans simply do not evoke the movement of these items). In this presentation, I will move the audience through the methodological changes we made and all the conservation decisions one must make when repairing these types of books, creating models for researchers, and utilizing animation software as a form of engagement and preservation.

Partnering with a digital specialist, we choose one mechanism/page in a book to animate. This page also undergoes scanning for the purpose of creating facsimiles and models that are eventually housed with the item and available for research. These models and facsimiles can be more roughly handled by those trying to understand the structure while still having access to the original they can see and carefully handle. The pdf model of the structure is also linked to the scanned book in our digital library, making it available for anyone to print out and re-create at home or in a classroom. The conservation issues that arise when animating movables and pop-ups with Adobe as well as 3D photogrammetry software will be discussed.

Considering the dearth of published papers discussing the repair of movables and pop-ups in professional journals, the history of the technologies that brought these books about is integral to understanding how to conserve these items back to working order and therefore will be discussed briefly even though imaging will be the main focus of this presentation.

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.

In 2017, Georges Braque’s Pitcher, Candlestick, and Black Fish (Vase et poisson noir), 1943, underwent a long-awaited treatment at the Menil Collection in Houston, Texas. The painting was cleaned and its wax-resin extracted following the removal of its lining; the methodology of the structural treatment is described in the proceedings of the Conserving Canvas conference held at Yale University in 2019. Technical imaging throughout the treatment led to a deepened understanding of the work’s early history by clarifying the design of a second underlying composition. It also led to the discovery of a third, as the removal of the stretcher and lining canvas, necessitated by the structural treatment, enabled infrared images of the back without their obscuring effects. Digital estimations of these earlier states bear striking resemblance to works from the 1920s and 1930s, thereby possibly extending the canvas’s lifetime by more than a decade. The extension of the canvas’s lifetime as revealed by technical imaging speaks to Braque’s well-documented tendency to rework or paint over compositions, while linen shortages during the Second World War could have provided additional motivation for repainting beyond creative impulse. The presentation will focus on Pitcher’s early history as revealed by technical imaging. Woven into that discussion will be a short explanation of how technical imaging informed the creation of the digital estimations.

Effective preservation strategies depend heavily on thorough material characterization. While recent years have witnessed significant advancements in the non-destructive identification of artists' materials in easel paintings, the technical analysis of paper-based artworks has lagged behind. This is primarily due to the unique challenges presented by paper-based art, including low analyte concentrations and the delicate nature of the substrates.

Our poster presents an ongoing research initiative aimed at addressing this gap by providing insights into the identification and degradation of green pigments found in collections of early printed and hand-colored works on paper. Our focus on green pigments is motivated by the complex conservation challenges they present, such as self-discoloration, paper substrate discoloration, and paper corrosion. Our research is also inspired by the significance of the extensive and valuable collection housed at KU Leuven's Maurits Sabbe Library. This collection offers a unique opportunity to study these pigments within authentic historic objects.

This poster presentation highlights "Nouissime Hystoriarum Omnium Repercussions" (often translated as "Supplement to Universal History") (1503) by Jacobus Philippus Bergomensis, a classic Renaissance historical chronicle renowned for its rich woodcut illustrations depicting various historical scenes and figures. Several folios featuring extensive applications of different green pigments in pictorial areas are selected for in-depth study. In the initial stage, we employ narrowband ultraviolet-visible-near infrared (UV-VIS-NIR) multispectral imaging (NBMSI) and fiber optics reflectance spectroscopy (FORS) as primary non-destructive techniques for data acquisition. The NBMSI, equipped with a 150-megapixel camera and integrated software and hardware, allows for imaging at 16 wavelengths ranging from 365 nm to 940 nm and fluorescence imaging at various combinations of illumination and filters.

Analysis of the reflectance spectra suggests that malachite is the primary pigment on these folios. However, further investigation of heavily degraded areas on folio one reveals the presence of non-malachite green pigments, potentially more prone to degradation due to their discoloration to brown and the presence of breakage in the paper substrate. Comparison to the Kremer pigment checker suggests that this is a type of green earth pigment. Notable variations in the visual appearance of folios with the same pictorial schemes and the application of this green earth pigment to the identical motif are observed. These variations are likely related to different degradation states of the pigments.

This variation in degradation states within the same object offers a unique opportunity to gain insights into the degradation of green earth pigments in historic objects. Our analysis of the reflectance spectra reveals significant changes in the optical properties of the pigments during degradation, including increased reflectivity in the NIR range and enhanced fluorescence above 590 nm when stimulated by 450 nm light. This approach holds promise for characterizing the degradation states of green earth pigments through NIR and fluorescence imaging. Further investigations are needed to confirm the pigments’ composition. Advanced methods for image analysis are under development to extract crucial chemical information. Additionally, the observed variations in degradation states on different folios provide insights into factors influencing degradation patterns, offering valuable information for preservation strategies.

Multispectral imaging (MSI) is an established cultural heritage technique for identifying materials and revealing non-visible information such as underdrawings and erased or faded text. While this technology has had limited reach due to traditionally high costs and specialized equipment and training, a low-cost, end-to-end, portable system was developed by RIT’s Imaging Science and Museum Studies Programs through a National Endowment of the Humanities grant (PR-268783-20), Multispectral Imaging System for Historical Artifacts (MISHA). MISHA images in the ultraviolet, visible, and infrared at 16 distinct wavelengths. This system has currently examined 200+ items (primarily parchment and paper) which lends to the analysis of the data to determine trends in the capture process, such as which wavelengths performed best with various materials. This research outlines the current progress of which wavelengths provide optimal results revealing non-visible information depending on an item’s various factors (condition, age, and so on). The results will form a “recipe book" for MISHA users, and other MSI systems, providing guidance on wavelength selection and processing techniques, derived from visual assessment and computational analysis of the MISHA dataset. The impact of this will be to improve MSI practices for cultural heritage professionals who do not have an imaging background and shortening an item’s exposure/handling time, reducing the potential damage to the item, and processing time and storage space for the multispectral images and software. For the research currently, results for various parchment and thermal paper items have been obtained with the potential to expand it to other items as well.