Light exposure (lux, UV, heat) is always a concern during exhibitions. How much light does St Cross get, and how can ancient manuscripts be protected while also being made accessible to visitors?
First, limiting exposure. Exhibitions of original material run for 3 months maximum. Pages exposed are changed regularly where that’s practical for the topic of the exhibition. Depending on their condition, books are closed whenever open hours are not planned for a few days in a row. Thanks to the condition survey and research following from it, I’m developing a ‘rota’ of manuscripts that can be produced as examples of various features, rather than getting out the old favourites every time.
The interior of St Cross, including the book cases used for exhibitions, does receive a surprising amount of natural as well as artificial light. The clerestory windows on the south side, although they are small and high, allow a lot of light for much of the day on the shelves on the north side of the nave. The above photo is taken with no artificial lighting on at all, around midday in early September. It is clear to see how much more direct sun shines on the upper than the lower shelves.
Thanks to the deep shelving and even deeper pelmets on top of the cases, the back of any shelf receives much less direct sunlight than the front. But manuscripts on display need to be as visible as possible – at the front of the case.
Also at the front of the case are these very bright and undimmable LED lights down both sides – they provide all the ambient light to the working area of the reading room as well as illuminating the objects on the shelves. It would be complicated and expensive to install temporary, movable conservation-standard low-level lighting in all these cases. The LEDs emit practically no heat or UV at all, and their intensity decreases dramatically a few inches away. But they are still pretty bright.
There is a simple and effective, if not ideal, solution: open manuscripts (or indeed closed books, as bindings suffer from sunning as well) are covered with a (new) acid free folder, or similar conservation-quality light card cut to fit, outside of exhibition open hours. This blocks pretty much all the light from sunshine and artificial lighting.
The free-standing exhibition cases are fitted with heavy card covers, which are also in place outside exhibition open hours. These are easier to put on and remove than their usual full-length wooden covers.