Assessment of indoor air quality and the risk of damage to cultural heritage objects using MEMORI^®dosimetry

Abstract

Air pollution is one of the environmental influences that degrade cultural heritage objects situated indoors. Other essential influences, such as temperature, relative humidity, and light are often well monitored. The presence of air pollutants is less often measured or included in risk assessment. The MEMORI ® technology presented in this paper was developed as a tool for easy measurement and assessment of the general risk of degradation of heritage objects situated indoors due to indoor exposure to air pollutants. MEMORI dosimetry was performed in locations belonging to English Heritage and Tate (both located in London) and the National Archives of Norway in Oslo, to assess air quality. The related damage risk for collection objects and the protection offered by display and storage designs was assessed. A high level of acidic effect was observed inside a number of showcases, and a high level of oxidizing effect was observed in some room locations. Relatively simple mitigation measures, such as constructing tightly sealed showcases using low emitting materials, installing active carbon absorbing media inside a 'microclimate' frame, and using cardboard storage boxes for paper, significantly improved air quality. Overall, implementation of such measures is likely to improve the preservation of objects and reduce conservation costs.

On the stability of mediaeval inorganic pigments: a literature review of the effect of climate, material selection, biological activity, analysis and conservation treatments

“…presence of residual salts/ uncarbonized moieties in carbonaceous pigments applied by using the fresco technique) [12,15,16]. Whitening is also reported for bone black [amorphous carbon with apatite Ca 3 (PO 4 ) 2 ] in oil binding medium, possibly related to the photodegradation of the aromatic structure, probably catalysed by lead (present as a siccative, or pigment) [17]. In another study, by the same authors, a variety of issues was identified related to the causes of discolouration of carbon blacks, such as the formation of lead carboxylates from the reaction of the siccative with the binder, or the alteration of lakes present in the mixture, or the degradation of the aromatic carbon compounds.…”

“…Huntite and dolomite, Mg-rich carbonates having formula CaMg 3 (CO 3 ) 4 [52]. The attack from polluted water can as well form gypsum CaSO 4 ·2H 2 O and the extremely soluble magnesium sulphate MgSO 4 , and calcite.…”

“…A variety of Ca, CaMg carbonates, and sulphates was used as white pigment (chalk, bianco di San Giovanni: CaCO 3 ; huntite: CaMg 3 (CO 3 ) 4 and dolomite: CaMg(CO 3 ) 2 ; gypsum: CaSO 4 · 2 H 2 O), as well as mixed with glue to prepare ground layers in northern and southern Europe, respectively [1,20,[43][44][45] and to prepare parchment for manuscripts [46]. The calcination of bones gives a white pigment mainly containing apatite Ca 3 (PO 4 ) 2 [1].…”

“…Relevant factors are relative humidity (RH, stable, fluctuating), temperature, illumination conditions, inorganic pollutants, and volatile organic compounds; the latter being extensively studied during the MEMORI project [3,4]. Moreover, information on the influence of other factors was collected from literature.…”

Monitoring the accumulated water soluble airborne compounds deposited on surfaces of showcases and walls in museums, archives and historical buildings

“…Dosimetry as a method of determining air pollution threat was made available by Grøntoft et al [9], under the MEMORI ® system. This consists of two small dosimeter samples; one dosimeter is covered with a thin synthetic polymer film and sensitive to oxidizing gases such as nitrogen dioxide (NO 2 ) and ozone (O 3 ), and with UV light, while the other is a potassium-rich glass sensitive to acidic gases.…”