The following is a guest post by Meghan Hill, a preservation specialist in the Preservation Research and Testing Division of the Library of Congress.
Conference season is upon us; a time to learn about exciting new initiatives in the preservation field and in turn to showcase our own work, to reconnect with colleagues from other institutions and welcome in those that are new. What I enjoy most about these events is the opportunity to continue learning, to have meaningful dialogue, and to exchange knowledge all in the pursuit of preserving cultural heritage for future generations.
My colleagues Fenella France, Chris Bolser, and I have been teaching courses on multispectral imaging for nearly the past decade, but this year the stars finally aligned to afford an opportunity to teach hands-on in our own lab again and with a wider variety of instrumentation to emphasize the Preservation Research and Testing Division’s (PRTD) holistic approach to noninvasive analysis. We demonstrated techniques that can suit the needs of different organizations with varying access to instruments, staffing, and budgets. We’re fortunate to have a fully equipped laboratory, but that’s not feasible for all institutions and that’s okay – you can still do a lot with even just a little.
We always strive to make science approachable, accessible, and practical, which starts by taking science out of the initial equation entirely. Learning to simply look at an object in a new way helps to spark more thoughtful research questions. When you no longer focus on the limitations of the technology and instead encourage curators, librarians, and researchers to ask complex questions about their objects, this type of investigative workflow inevitably allows us to add a new depth of knowledge about our collections, understanding more about the historical and cultural provenance within these original sources. It also facilitates investigating impacts on larger collections, not just individual items.
Let’s consider the document below and see beyond just its written words. (We love dirty documents. They’re so much more interesting to explore and give clues to their use and lifetime before they came to the Library.) We could investigate the inks and determine if the annotations are the same as the body text. We could identify the blue and red pigments. We could see if there’s evidence of how the scribe ruled the page before writing. We could look at the holes and assess their origin, if they were from stitching or possibly insect damage. We can look at areas of staining or even areas of loss and suppose how the document may have been handled, used, or stored. Preservation science can be a forensic-like investigation of an object’s materiality and what that says about the greater historic context of the object. Watermarks can inform provenance, pigment identification can determine sourcing of raw materials and inform trade routes used at the time, evidence of creation techniques can suggest contemporary technological availability.
We continue by demonstrating how each instrument we use for analysis adds an additional layer of information about a cultural heritage object. For example, spectral imaging can map which inks are the same and which are different, X-ray and reflectance spectroscopies will tell us the elemental and molecular composition of each ink, and infrared spectroscopy can tell us about the inks’ binder or any coatings on the surface of the parchment to allow it to accept the ink when written on.
But how does one consider doing all of that from a basic instrumentation set up? As many past blog posts have demonstrated, we start with multispectral imaging, a fantastic tool for mapping the material components of an object (pigments, inks, substrates, and coatings) across the entire image. It can also recover erased or obscured content and identify watermarks. A single-color image can be broken into its red, green, and blue channels in most photo editing software. Adding in a shot under a broadband ultraviolet and infrared light can provide two more channels to create a five-channel multispectral stack to start investigating. Inexpensive microscopes can provide detail otherwise impossible to see, like the order in which rhumb lines were drawn onto a nautical map. Simple spectrometers, repurposed from its use as a wall paint color analysis tool, can provide color information about a pigment and help to identify its origin.
I look forward to continued collaboration this season and next and the exchange of new and innovative ideas. I find that bringing together different specialized areas of knowledge, expertise, and points of views is invaluable in adding to and disseminating the historical understanding of cultural heritage collections and perpetuating the innovation of their preservation.
To find out more about the Library’s collections and the preservation activities necessary to keep the largest library in the world available, be sure to subscribe to this blog and check back weekly!