AIC's 53rd Annual Meeting

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The lunch session is designed to delve into the fundamental aspects of multiband (MBI), multispectral (MSI), and hyperspectral (HSI) imaging in a welcoming setting that invites learning, inquiry, and exchange. The first part of the session will include an invited presentation on light-matter interaction focusing on the phenomena that provides the foundation for MBI, MSI and HSI. The second part of the session shifts from phenomena to technique and will include two invited presenters to cover MBI and imaging spectroscopy (MSI and HSI). The presenters will define these techniques and their principles of operation, highlighting advantages and limitations of the techniques with case studies of applications and media. Presenters will also touch on instrumentation and requirements for setup, calibration, processing, and analysis. Other important topics include the knowledge required to acquire and interpret spectral data and variations in equipment setups and corresponding general price points. Each of the presentations will be followed by time for Q&A and a resource document will be assembled to share with participants. The session will be recorded as an intended resource for the community.

The session is continuing to be co-developed with the invited speakers and representatives from Imaging Working Group (IWG), Book and Paper Specialty Group (BPG), Photographic Materials Group (PMG), and Research and Technical Studies Specialty Group (RATS).

The lunch session fits into a larger imaging program at the Annual Meeting that will include a joint specialty session looking at case studies of applications and interpretation (BPG, PMG, RATS), and a concurrent general session (pulling together a range of media, techniques, and applications). The lunch will be held at the beginning of the conference to lay a foundation for the joint and concurrent general sessions.

Calling all Imaging Working Group members and fans - join us for a studio tour at the Minneapolis Institute of Art led by Charles Walbridge. The tour will start at 6:30 pm followed by an informal "pay as you go" happy hour at the museum's cafe - Agra Culture. If needed we might be able to offer a second later tour. The cost is free - attendees will need to provide their own transportation and purchase their own food and drink.

Space is limited in the tour and registration is required. Please add the event to your Annual Meeting registration.

The Cooper Hewitt, Smithsonian Design Museum has a collection of approximately 300 sketches by Jan van der Straet (called Stradanus) a 16th century court artist to the Medici in Italy. A group of these drawings may have important information on the verso written with black chalk, but unfortunately, have been lined with paper. The presence of inscriptions/drawings on the verso has been detected using transmitted visible light when the media is ink but not for chalk. To minimize carrying out interventive conservation treatment to remove the linings from the fragile drawings, transmitted IR imaging was investigated to determine whether the technique could be used to detect chalk drawings on the verso without removing the linings from the drawings.

This initial imaging investigation involved four Stradanus drawings. Reflected and transmitted visible light and IR images were acquired of the recto and verso of the drawings. The investigation started with the three drawings that had the paper linings removed and had known verso chalk drawings. The first step involved testing whether transmitted IR imaging of the recto could resolve the verso chalk drawing which could be verified with reflectance images of the verso. Preliminary processing, during the image acquisition, indicated that transmitted IR and image processing could detect the verso drawing, so the next step involved imaging one of the unlined drawings with a paper support placed behind the object to mimic the lining. The final step involved the imaging of a fourth drawing that had not had the paper lining removed and it was unknown whether there was a verso chalk drawing. 

Transmitted IR images on their own did not provide much information, but image processing, both false color and image subtraction, was essential for further analysis. The false color image processing involved combinations of reflected and transmitted visible light and IR images including newer techniques that have only been introduced and used on paintings. The image subtraction processing was the difference between the reflected and transmitted IR images. The most promising methods were the image subtraction and the false color processing using transmitted visible and IR images. The image subtraction was able to fully resolve the verso chalk drawing for one of the drawings (both with and without a tertiary support), but the same processing was less conclusive for a verso chalk drawing that did not have identifiable features. When the difference mode was less conclusive, some of the false color processing seemed to be able to reveal some features that do not correspond with the recto ink drawing and could suggest that there might be verso chalk drawings.

The imaging of four Stradanus sketches suggests that transmitted IR imaging and additional processing is promising for detecting verso chalk drawings without removing the paper lining, but the results were not always definitive. Additional testing with a larger subset of drawings is needed to further investigate the potential of transmitted IR imaging and image processing.

Colorant Detectives: An Interactive Dichotomous Key for Multiband Imaging

L. M. Ramsey, The Metropolitan Museum of Art

The Colorant Field Guide is an online, interactive tool designed to aid in the visual interpretation of colorants on paper based on their responses to visible (VIS 380-650nm), ultraviolet induced fluorescence (UVF 420-650nm), ultraviolet reflected (UVR 320-400nm), and reflected infrared radiation (IR 780-1100nm [850 peak]). By employing standardized vocabularies and metrics like CIELAB and Munsell color systems, the guide ensures rigorous, reproducible, and communicable results.

Rather than relying on static research papers, black-box algorithms or automated false color post-processing systems to locate and provide results, users must navigate through a decision tree that exposes them to the various factors that influence sample behavior, including light absorption, fluorescence, and reflectance. This process demystifies colorant response by breaking it down into manageable steps, helping users to build a strong foundation of knowledge that can be applied in real-world conservation scenarios.

Transparency in documenting light/radiation sources, filters, and post-processing techniques is emphasized to achieve consistency and comparability across institutions. This approach fosters collaboration and enhances the collective knowledge base in conservation while addressing the inherent uncertainties in multispectral imaging and dichotomous identification methods.

Building a dynamic dichotomous key involves both a logical framework and technical implementation to ensure usability and functionality. I designed it to be simple and effective using basic HTML, CSS and JavaScript languages to make the key interactive, process user input, and display results dynamically. To translate the flow chart to an interactive framework, it was important to list each colorant and their responses in a standardized order. This order helps build a logical, hierarchical flow. At each decision point, users are guided either to the next question or to a result, allowing for the possibility of future expansion.

In addition to the key, I am developing a pictorial atlas of colorants recorded under these imaging techniques to serve as a visual reference. This project is intended to be publicly accessible and expandable, allowing users to submit data that meets established criteria. These submissions will be clearly credited, promoting transparency and collaboration. By encouraging contributions, this tool fosters a cooperative research environment, enriching the field of cultural heritage preservation and providing a shared resource for the broader academic community.

Dichotomous keys have long been valued in education, particularly for teaching critical thinking, systematic problem-solving, and observation skills. As multiband imaging becomes a standard practice in more institutions, this accessible tool will help ensure visual literacy in the conservation field remains strong.

Both multiband and multispectral imaging can provide a wealth of information about material characteristics and condition—with insights derived from qualitative and quantitative comparisons of images captured at different wavelengths and with different excitation sources. Workflows for these types of imaging often require costly additions to existing setups: IR-modified and/or monochrome cameras, filter sets, apochromatic lenses, and even licenses for proprietary image processing software, the sum of which can present a significant cost barrier. Certain equipment is essential, such as modified UV-VIS-IR full spectrum color or monochrome cameras. However, it is possible to perform multiband and multispectral imaging without the added cost of an apochromatic lens—one which produces a single focal plane across all wavelengths. The main challenge, however, with using a regular (achromatic) lens is the need to re-focus for each filter band, leading to registration issues across the entire set of images captured. This misalignment must be corrected post-capture not only to remove visual inconsistencies in false-color images but also to carry out any further computational analysis, such as Principal Component Analysis or Spectral Angle Mapping. 

With this issue in mind, this project has focused on developing a low-cost, open-source method for automating the registration of image sets generated from multiband and multispectral imaging workflows. Drawing on research beyond the field of art conservation, we have adapted Python code from a recent publication on vision-based robotics grasping in order to identify the specific feature-based pixel coordinates necessary for image registration. Specifically, the code utilizes an Open Source Computer Vision Library (OpenCV) tool called template matching as an alternative to feature-point detection algorithms or more complex object-detection models. In total, this method requires the addition of only a few printed paper targets and is designed to be integrated easily into existing multiband and multispectral imaging workflows. The current iteration of our adapted Python code can be executed directly from a computer’s command line, and we are hoping to create an ImageJ/FIJI plugin to make the script more readily available and user-friendly.

Northwestern University Libraries (NUL) is home to over 3,000 Arabic script materials from West Africa. Part of the Herskovits Library of African Studies, these manuscripts come primarily from northern Nigeria and cover subjects including history, theology and astronomy. Most are Arabic, but some are Ajami – non-Arabic languages written in Arabic script. The size, scope and uniqueness of these underrepresented collections, along with increasing global scholarly interest, make them a priority for conservation and digitization. In collaboration with curatorial, cataloging, and digitization staff, the NUL Preservation Department has established standardized protocols to survey, house, treat, and – using a VSC®80 forensic questioned document examination workstation – capture a range of multispectral images (MSI) that are integrated into the digital repository, adding a degree of materiality to the imaged West African manuscripts.  

Paden 417 (مختصر في فروع المالكية), a copy of the “Mukhtasar” of Khalil b. Ishaq b. Musa al-Jundi, a fourteenth-century handbook of Maliki legal principles, is one of the oldest, largest and most complex manuscripts we have worked on and serves as a case study. It is comprised of 230 individual leaves of handmade paper contained in a later leather wrapper. The primary text is written in neatly ruled lines using brown and red inks, with commentaries and annotations filling virtually all other areas of the paper in brown and black inks. The paper is brittle and discolored, with extensive losses along the edges. In preparation for imaging, the manuscript received over 300 hours of treatment from ten different current and former staff members. Our collaborative approach is not unique to this object, but it was critical for addressing the challenges presented by Paden 417, which would have been daunting and laborious for a solo conservator.  

Many of the Arabic manuscripts lack colophons or other means cataloguers use to establish clear provenance, so to understand their history and production, we must rely on the physical objects. NUL purchased a VSC®80, which allows us to quickly and consistently capture and annotate a wide range of MSI of watermarks, inks, ruling lines, and other materiality of the manuscripts.  

As one exciting example of how MSI may be used, portions of Paden 417, along with a selection of MSI files, were recently examined by scholars at the Centre for the Study of Manuscript Cultures in Hamburg, Germany. Although they had actual manuscript pages, the enhanced images of the watermarks allowed them to date the manuscript to the mid-16th century, making this one of the earliest written examples of Hausa Ajami.  

As of this writing, Paden 417 has been treated, housed, and VSC®80 images of select pages have been captured.  Digitization is underway and collation of this fragile object will follow. We anticipate that the manuscript and associated MSI will be publicly available in the digital repository by early 2025. Incorporating MSI into our digital repository augments the standard digital images, opens the door to scholarship worldwide and presents future opportunities for collaboration on machine learning and generative AI initiatives.

For the past three years, the Biblioteca Capitolare di Verona, the oldest library in the world, has been the site of a manifold collaboration among four scientific- and two scholarly teams representing eight countries to solve one of the most intractable problems in cultural heritage imaging. The Palimpsests in Danger project was convened to address the illegibility of two of the most important palimpsests in existence: the Verona Gaius, the only remaining witness to Roman law, and the Verona Vergil which, along with known undertexts containing Euclid and Livy, we revealed to contain a new Apuleius.

Over two centuries, both palimpsests had been treated with multiple layers of two different chemicals: oakgall reagent and Gioberti tincture. The manuscripts, their parchment weakened by the reagents’ corrosive acids, were then disbound and set in gelatin. Creating a chemical layer that overwhelms fluorescent response from the parchment and attenuates the infrared, the chemical reagents proved to be nearly insuperable impediments to even state-of-the-art multispectral imaging.

To learn more about the precise nature of the challenge and to find effective recovery techniques, the Early Manuscript Electronic Library, supported by the Lazarus Project, the University of Hamburg, and the University of Torun, organized a program of material analysis, new imaging modalities, and innovative image processing techniques all supported by a grant from the Arcadia Foundation. XRF, XRD, and Raman spectroscopy furnished specifics about inks and reagents, whilst scanning XRF, IR Reflectography, RTI, and the newly-developed techniques of IR Fluorescence MSI and scanning Optical Coherence Tomography (OCD) yielded new images of the undertext.

This talk will reveal our results for the first time, covering the exact chemical and imaging challenges of chemical reagent-damaged manuscripts, the advantages and drawbacks of each technology and processing technique used, show never-before-seen images of the undertexts from the Gaius and the Vergil palimpsests, and make recommendations for best practice. Above all, it will highlight the importance of cross-disciplinary collaboration among scientists and scholars from the US (EMEL, University of Rochester, Rochester Institute of Technology, UCLA) and Europe (University of Hamburg, University of Torun, the Sorbonne, Oxford University, the Biblioteca Capitolare di Verona).