AIC's 53rd Annual Meeting

The Victoria and Albert Museum (V&A) has recently implemented a novel lighting policy (discussed in detail in VanSnick & Gaspar, 2024) - seeking to strike a balance between the display of light-sensitive objects and their long-term preservation. This work offers an evaluation of the practical rollout of the policy, refinement of process, and stakeholder uptake.

This policy works by whittling down collection on display to those objects that have the most pressing light vulnerabilities, looking experimentally at those objects, and using that new information to inform how we select vulnerable objects in the future. The first step is determining light vulnerability on a broad material level, flagging objects on display made from materials academically known to be highly light sensitive. These broad strokes are of huge benefit as it ensures that the first action of this policy will target those objects with the potential to be currently undergoing massive light damage. The second phase invites curatorial colleagues to assign a relative value each object in the group of highly light sensitive objects, allowing resources to be targeted in on the most exemplar objects which are materially assumed to be highly light sensitive. Where possible, objects that are highly light sensitive will be rotated out of display in a time period dependent on their rating value. Where rotation is not possible objects are examined experimentally using Microfademetery Testing (MFT).

Objects are unique in their vulnerabilities and these vulnerabilities are not as linear, consistent and predictable as one might expect. Experimentally analysing objects using MFT has the potential to bring their actual current light vulnerability into sharper focus. Given the vast size of the V&A’s collection, it is truly unfeasible to experimentally analyse every object - however this policy allows precise targeting of experimental resources to the places in the collection where they are most immediately needed. The lessons learnt about discrepancies between the assumed light sensitivity and the current experimental reality found are fed back into the initial stages of this process, allowing us to redirect resources to more vulnerable objects. For example, MFT conducted on Chinese, Japanese, and Korean lacquerware as part of this process has found this material to generally be drastically less sensitive to fading in practice than was academically thought. Not only does this mean that these objects can have far greater lifespans on display, improving access and ensuring we are focussing on the collections that need us most. 

This is not a static system - it is a cyclical process that edits and allows a more accurate picture of the collection’s sensitivities to coalesce in each iteration. It allows us to learn about our collection today and to react as the composition and the needs of our collection evolves over time.

The light sensitivity of works on paper is an important issue for any paper-based collection with regular exhibition cycles. The main concern is to protect the media from light-induced color changes, and MFT is a proven in-situ method for predicting these changes. As a substrate, however, white paper and especially rag paper is generally considered to be quite stable, with the exception of wood-containing and colored paper, which are considered light-sensitive according to the lighting guidelines. However, within the broadly defined class of white papers – which have been the most widespread worldwide since their emergence – there are also lignin-free white papers that are affected by moderate exposure to light. Our research group – three conservation scientists and five paper conservators collaborating from a print and drawing collection, a conservation science research laboratory, and two universities – studied typical light sensitivities related to compositions of paper and the ability of MFT to predict light-induced change in a broad range of the most typical white paper compositions.

We prepared nine sets of 37 papers divided into four compositional groups that represent papers across time. Three sets were aged in UV-filtered museum and commercial gallery exhibition-simulated settings (LED, mixed fluorescent/daylight, up to ca. 2.5 Mlxh), four underwent cyclic light-dark aging with or without pre-aging, and two sets were micro-faded by two commercially available MFT devices, one with a xenon source, the other a LED source. Using this test setup, we evaluated the influence of paper components on the color development of the papers during these different natural and accelerated aging conditions and compared them with the MFT results. The color change data of all exposures are given in Blue Wool Scale (BWS) by comparison to co-exposed Blue Wool Standards. 

Most white papers in exhibition simulation fell into the relatively stable BWS 2.5–4, but aged rag papers and papers containing ligneous and OBA papers ranged at BWS 1.–2.5. The predominant color change tended to be fading, but highly optically brightened (OBA) papers of low quality darkened. Groundwood and other high-lignin papers changed to yellowing after initial fading. Iron-contaminated papers without a significant alkaline reserve also tendentially darkened. Previous light-dark aging cycles had an effect on the type of color changes caused by light. Both MFT types and the cyclic light-dark aging predicted the papers’ sensitivity adequately compared to the simulated exhibition exposures and identified the most light-sensitive gelatin-sized rag papers and lignin-containing papers. However, predicting the color change of OBA-containing papers proved to be much less reliable. The color change of the papers that were exposed to LED in the exhibition-simulation was better reproduced by LED-MFT than by xenon-MFT or cyclic light-dark aging.  

We hope that the research results of the recently completed project will provide a clearer idea of the role of white paper in predicting the light sensitivity of artworks on paper using MFT. 

Our collaborative project was funded by the Germany Research Foundation 2021–2024.

Preservation Programs at the National Archives and Records Administration (NARA) investigated the characteristics of iron gall ink (IGI) in low or no-oxygen environments. NARA has vast holdings of 18th,19th, and early 20th century documents with iron gall ink. With the 250th anniversary of the Declaration of Independence, conservators and scientists seek to understand more about long-term display of sensitive IGI documents. In the past, NARA has used sealed anoxic encasements for some permanently-displayed iron gall ink documents. However, recent research into IGI behavior in anoxia [1] as well as material and structural differences between the majority of paper-based documents in NARA's holdings and other treasured national records on parchment meant that the use of a low oxygen display environment needed to be examined. 

Scientist Bruce Ford previously demonstrated that fading of iron gall ink is somewhat reversible in the dark but that anoxia diminished this reversion potential. His experiments exposed ink to light levels equal to several decades of display exposure, followed by a period of darkness that allowed ink to revert overnight. We sought to conduct a similar experiment, but with a closer match between typical exposure and rest periods to exhibit conditions. Additionally, we wanted to know if IGI reversion potential could ever be exhausted or would change with past treatment history. Subsequently, we designed experiments using an automated LED MFT (2700K white LED, ~3.1Mlux) in an atypical manner. We repeatedly exposed 19th century, post U.S. Civil War era, non-record samples and paused for reversion periods in the dark on the same spot. We tracked incremental and overall change in color (ΔE00) and L*a*b* color space parameters. We also tracked and controlled temperature and humidity as much as possible to prevent movement during test periods (up to 1.5 weeks) and kept the dose for each exposure as low as possible (0.04-0.4 Mlux-hrs.), only inducing enough change required for reasonable signal to noise ratios. We performed mock de-silking and delamination treatments on historic samples to mimic the condition of many NARA holdings. Treated ink required higher dosages of light to induce the same amount of change as non-treated IGI. We conducted multiple cycles of low-dose MFT both in air and anoxia and were able to reproduce Ford’s result showing reversion in air, and significantly reduced reversion in anoxia. We investigated the nuances of reversion in each of L*, a* and b* under each condition. After several tests in anoxia, we reintroduced oxygen up to 2% concentration which showed a returned ability to revert. MFT results were also compared to an experiment with 2 klux LED lamps (up to 4.5Mlx-hrs) where no visible change was observed. This indicated reciprocal failure, however these results still have important implications for display design options for iron gall ink records.

Works Cited

1. Ford, B. 2014. “The accelerated light fading of iron gall inks in air, hypoxia and near-anoxia.” In ICOM-CC 17th Triennial Conference Preprints, Melbourne, 15–19 September 2014.