Dosimeters for indoor microclimate monitoring for cultural heritage

M.Odlyha, C.Theodorakopoulos, D.Thickett, M.Ryhl-Svendsen, J.M.Slater and R.Campana

This paper describes the performance of dosimeters based on the quartz crystal microbalance and demonstrates that measured changes can be correlated with damage to artifacts and with environmental conditions. The work has been performed in the framework of two EC projects where the emphasis has been on damage assessment. In the MIMIC project: [Microclimate Indoor Monitoring for Cultural Heritage Preservation] [EVKV-CT-2000-00040], piezoelectric quartz crystals (PQC) were covered with organic coating. It was the damage to these coatings which was assessed after exposure to a range of environments [1]. The eight-crystal arrays were accommodated in custom built modules and exposed either as passive samplers or as continuous monitoring devices, which recorded weight changes in real time. The Artists' materials, resin mastic varnish and egg tempera, were selected, since mass spectrometric studies had shown that there was a correlation between chemical change and exposure to light [2, 3]. Accelerated light ageing tests of the coated crystals then demonstrated that changes were correlated with changes to the oscillation frequencies of the coated crystals. Furthermore, real time monitoring of exposure to controlled and varied levels of NO2 and RH provided evidence of a systematic variation in the frequency shifts of the coated crystal arrays [1]. Crystal arrays were also exposed in rooms containing mixed collections in museums, historic houses, and castles, where climate and pollutants, were being monitored [1]. The results obtained from the integration of climate, dosimeter, and chemical data will be discussed in this paper. In the SENSORGAN project (contract no. 022695: Sensor System for Detection of Harmful Environments for Pipe Organs) a lead coating was used. Lead was selected as it was shown in the COLLAPSE project (Corrosion of lead and lead-tin Alloys of Organ Pipes in Europe) [4] that lead was the main constituent of historic organ pipes and that damage occurred as a result of the emission of volatile organic acids from the wood of the wind-chest. Modules containing crystal arrays were exposed to accelerated ageing in laboratory cabinets where levels of acetic acid were monitored. Site monitoring was performed in the organs in two churches: (1) the Minor Basilica of St. Andrew the Apostle (1611) in Olkusz, Poland (2) St. Botolph without Aldgate (1704) London, England.