Context 159 - May 2019

30 C O N T E X T 1 5 9 : M A Y 2 0 1 9 Anglo-Saxon Treasures of St Cuthbert display. The conservation project consisted of significant restoration of the decaying stone of the roof vault and walls, and innovative solutions tackling key defects to the space. Tests had revealed that the space had a relative humidity of between 60 and 85 per cent, caused by moisture ingress through the fabric.This, and frequent changing air temperatures between 9 and 18 degrees, meant that magnesium sulphate salts, inherent in historic lime mortars, were being activated.This led to the crypto-florescent cycle occurring regularly between crystal and liquid states of the magnesium sulphate salts. This was causing damage to the UK’s only remaining stone-vaulted kitchen. To control relative humidity and combat the decay, the Great Kitchen’s concrete slab floor was removed and replaced with a limecrete breathable one which incorporates a floor duct. The installation of a new conservation-focused heating system then enabled air to be ducted through the floor at low pressure over finned heating pipes. The new environmental control system is a hybrid solution which includes close control air conditioning with plant located in confined spaces concealed in wall structures. The air conditioning has been set up so as to be able to dehumidify, if other means fail to adequately control the environment, but it cannot actively introduce moisture. Electrical services were routed under the floor, but sensitively located above archeologically sen- sitive layers.The room is protected by a carefully concealed aspirating smoke detection system. By improving and managing these conditions using traditional, conservation repairs, the new mechanical engineering systems have delivered stable and safe conditions for the fragile Anglo- Saxon silks, manuscripts and artefacts. The interior was also relit to display the architectural and archaeological qualities of the room. The environment in each of the spaces is now stable and within target ranges enabling the rooms and their contents to be enjoyed by thousands of visitors. The relative humidity of the kitchen, for example, is now averaging 49 per cent, with temperatures that gradually change through the seasons to maintain this level. The oscillation of magnesium sulphates has been stabilised. As a result the cathedral is now able to display in passive cases the Anglo-Saxon- period silks, early medieval manuscripts, and the Anglo-Saxon coffin associated with the shrine of St Cuthbert. Louise Priestman is a conservation accredited architect who works for Purcell Architects. Installing airconditioning in the Collections Gallery enabled the display cabinets to rely on passive environmental controls alone The Great Kitchen and the ‘Treasures of St Cuthbert’ display: air ducted though a floor trench conditions the environment