Collections of books, drawings, photographs, maps and letters are full of organic materials, such as paper, parchment, leather, wood and textile. These materials are liable to natural deterioration. Our storage conditions make sure that the aging processes are minimised, but since the collections are used, certain risks for the stability of the objects cannot be ruled out. The essence of preservation is making sure that the objects can be safely used and remain available for future researchers at the same time.

The work involves many different activities and requires in-depth knowledge of the various materials the objects are made of. Hands-on treatments are part of the job, as well as minimal consolidation activities that merely stabilise the condition of objects. Sometimes items need cleaning, or we replace improper old storage materials with protective folders or boxes. When prints or drawings, or manuscripts or books are requested for exhibitions, they need specialist care. It is crucial that the method of mounting leaves no traces of adhesive or further intervenes with the object. Items may also require treatment and support when they are to be digitised.

The primary rule for the conservation of the special collections is to intervene as little as is necessary in order to restore the accessibility of the objects. The aim is always to preserve the object’s characteristics and the historical traces of use. The second principle is reversibility. This means that no original material is removed, and that all added materials, such as repair paper or adhesives, do not affect the condition of the original and that they remain removable, should this be required in the future. In addition, the condition of the objects is documented in detail prior to any treatment. This way, physical information that is accessible only in the damaged condition will be preserved for researchers even after treatment.

The intense use of the general collections requires a slightly different approach. The ambition is still to preserve the original bindings of these books but the intervention should allow for a more robust use. The 19th century items present the biggest challenge; the materials and constructions of these books are often very poor. Sometimes it is necessary to alter the construction in order to maintain the accessibility, but reversibility and careful intervention remain important principles.

Preventive conservation means that the storage and handling conditions are optimised in order to slow down natural deterioration. There is climate control in the storage rooms with a stable relative humidity that is favourable for leather, parchment and paper (50%) and the temperature is relatively low (18 degrees C, even lower for the photographic collection). Whenever possible, the objects are housed in boxes or otherwise packed, to support them on the shelves and protect them while transported. These packing materials are developed for long term storage.

In addition, we provide supports for the books and other items when they are handled and used in the reading room. Maps are handed out in protective folders and drawings, prints and photographs are mounted in protective housings. In the reading room, we stimulate the use of weights – the so-called ‘snakes’ – to help keep a book open, and cushions are available in different sizes to support the books, while flat materials are best consulted without such supports. All these measures contribute to the preservation and enjoyment of our collections.