This is a guest post written by Andrew Davis, a chemist in the Preservation Research and Testing Division, with contributions from Cindy Connelly Ryan, a Preservation Specialist in the Conservation Division in PRTD, and Sonja Reid, a Preservation Specialist in the Conservation Division. Andrew works to understand polymeric materials in the Library’s collection, such as paper, adhesives, and audiovisual materials and also researches the effects of light and the environment on collections objects.
Staff at the Library of Congress love to showcase the collections with the public. While there is a lot to see online, our physical exhibitions are a highlight for those who can come in-person. Exhibitions involve a careful balance of letting the most people as possible see the collections while also preserving them. We want you to be able to see them now, and we want someone to be able to see them hundreds of years from now.
As exhibitions are being planned for new galleries, the Conservation Division (CD) and Preservation Research and Testing Division (PRTD) have been collaborating to assess the items selected for display. As part of this process, staff in CD typically review every item in an exhibition to determine how to safely display it. This review includes evaluating possible treatments, the kinds of mounts or cradles for display, and various ways that lighting might affect the item.
To understand how these materials might change under prolonged light exposure, the scientists in PRTD use micro-fade testing (MFT). This technique uses a tiny and focused spot of light paired with a spectrophotometer, which is an instrument that measures changes in light intensity and color. Subtle color changes detectable by the instrument before the human eye can perceive them, paired with small test spots, allows us to directly test a material and learn important information about its potentially unique response to light. While we know general lighting guidelines for various materials, this method allows us to make display recommendations for each unique item.
While we are used to being concerned about old documents, sometimes the newer items are the most prone to fade. For this work, conservators chose items for testing which were potentially most light sensitive, for the team to determine if they could be safely exhibited for six months. These items ranged from modern photography and inkjet prints to hand-written maps, recipe books, and journals dating from the 15th to 20th centuries, to printed books and posters, to an 18th century Buddhist Thangka.
Micro-fade testing of a photographic print by Salwan Georges, with the focused test spot shown on right for scale (from photo subject’s lanyard). Photo credits: Andrew Davis, PRTD.
There was one large additional wrinkle to this recent undertaking. As of this month, we’ve been living in a world largely defined by various pandemic responses for 2 years. The large scope of this particular analysis, paired with a virus that stubbornly refused to give us a break, made this work challenging. We had a timeline in mind to ensure that our curatorial and exhibits colleagues had plenty of time to consider our results, for good or bad. So how do we safely coordinate all the moving people, equipment, and objects that are needed for testing when constrained by distance, masking, and unpredictable schedules? We’re not the only workers struggling to choreograph this dance, but the scale and timing of this work was a unique experience for CD and PRTD.
One set of items we tested for exhibition tied together the ideas of newer items and in-person experiences: a set of posters documenting the Covid-19 pandemic.
“Mask Up” poster on left, with masked preservation staff (Sonja Reid and Cindy Connelly Ryan) on right. Photo credit: Eric Monroe, PRTD.
With an ever-swirling mix of Greek-lettered virus headlines, we did more online preparatory work for this analysis than ever before. In years past, we may have knocked on the lab door across the hall and asked our colleagues to come and see if they thought one spot on an item was a better location than another. But with weeks of testing ahead, objects needing shuttling between curators and conservators and scientists, and possible week-to-week quarantines of school and family, we replaced door-knocking with emails, spreadsheets, and marked up slides. We took as much advantage as possible from the Library’s excellent online catalog to inspect high-resolution images of the items for testing.
Screenshots from online planning for item testing, showing an item image with markups (left) and a larger multi-item priority-planning document (right). Image credit: Andrew Davis, PRTD.
“La Teacher”, one of the pandemic-related posters we tested, was an apt inspiration of our efforts here. (As an aside: tremendous plaudits to all the online students and teachers out there. Wrangling professional colleagues across a flaky internet connection is not fun, but it’s nowhere near an algebra class.)
“La Teacher” shown on left, with the poster undergoing testing shown on right. Photo credit: Andrew Davis, PRTD.
Regardless of our online efforts, this work eventually needed a laboratory bench and PRTD’s hands to run the testing. This set of items was larger, both in quantity of items and in physical size of some items, than any we had undertaken in one concerted approach. Our online planning work made our onsite lab work flow pretty smoothly. We were able to make the most of the days when we were together in lab by grouping smaller objects with more straightforward testing sites of interest. We could identify very complicated objects that needed an entire day for themselves and made sure to schedule enough hands onboard to handle the more unwieldy objects.
Testing of Winter count, one of the larger items analyzed. Photo credit: Cindy Connelly Ryan, PRTD.
PRTD ultimately analyzed the light sensitivity of nearly 30 items (with over 200 test spots) across 14 days in the lab, with many more days for preparation and analysis. It’s a good thing we did, as we identified 10 items planned for exhibition with light sensitivity beyond our most sensitive standards. These most highly sensitive items came both from old objects (the oldest from the 15th century) and new ones (the most recent from 2013). There were plenty of curious results too. A 2015 photo print had a yellow dye showing signs of free radical photochemistry where oxygen inhibited its initial reactivity. The section titles on a 15th century cookbook were exponentially more light-sensitive than the main text ink. A mixed-media artists’ book had numerous light-sensitive elements, including highlighter pens, colored paper, and poster paint, but the most sensitive element proved to be the plain white copy paper’s fluorescent brightening agents. Clearly the conservators’ experienced eyes identified meaningful items for testing, and PRTD’s skills crucially informed their questions.
As a personal aside, I keep thinking about those items related to these past two pandemic-driven years. In CD and PRTD, we frequently work with ancient manuscripts, historic photos and prints, and obsolete audiovisual materials. But PRTD works much less frequently with collection objects so close to our own times, much less ones mirroring the ongoing concerns we have for each other in the Library’s preservation spaces. These prints capture just a fraction of the history we’ve all struggled through in some degree or another these past two years.
Who can say when we’ll all be wandering between lab spaces again for spontaneous brainstorming about testing questions, rather than pulling up video meeting screens. But hopefully someday soon you will be able to come and see these items under the gallery lights. Until then, we keep going.
“Keep Going” poster, with the light spot on this poster during testing show on right. Photo credit: PRTD.