Conservation risks for paper collections induced by the microclimate in the repository of the Alessandrina Library in Rome (Italy)

Abstract

The Alessandrina Library was founded in 1667 by pope Alexander VII Chigi and is nowadays housed in the Campus of Sapienza University of Rome (Italy). Within its Ancient (mostly made of rag paper) and Modern (mostly made of contemporary paper) collections, it includes more than one million books produced from the XVI to the XXI century. In 2019, six thermo-hygrometers were deployed in its multi-storey repository to monitor temperature (T) and relative humidity (RH). Hourly T and RH data collected over 2 years allowed us to evaluate spatial and temporal thermo-hygrometric distributions and to carry out a comprehensive assessment of the climate-induced risks (mechanical, chemical, and biological deterioration mechanisms). Vertical temperature gradients associated with unstable conditions occurred in winter, resulting in upraising air flows up to the ceiling. The risky short-term RH fluctuations (EN 15757:2010) were determined to avoid mechanical stress in case of loans, relocation, and consultation. The Time Weighted Expected Lifetime (TWEL) index was used to evaluate the chemical risk for different paper-based collections as a function of their acidity and degree of polymerisation, also considering the typical response time of paper books to T and RH changes. The TWEL calculation estimated that the durability of acidic paper was around 300 years and highlighted that rag paper could be subject to cellulose hydrolysis only in summer and autumn, while contemporary paper was mostly at no risk. The risk of mould germination (Sedlbauer diagram) was possible on few days in Autumn, while the production of insect eggs (Brimblecombe empirical function) was favoured during approximately 42% of time over the year. In addition, illuminance and colorimetric measurements (performed on selected book covers) showed that light-sensitive objects could be exposed to the photodeterioration risk in the east-facing side of the repository. Although the investigation focussed on a specific case study, a similar approach could be effectively adapted to most library and archival repositories conserving paper-based collections.

A Statistical Approach for A-Posteriori Deployment of Microclimate Sensors in Museums: A Case Study

“…Interpreting the results of principal component analysis and cluster analysis is a complex task, as users need to have statistical skills and both require the use of advanced computer programs. In fact, several types of data pre-treatments can be applied in PCA, leading to different results [13,25]. However, these methods have the advantage of revealing hidden relationships between variables in a more overarching way than just looking at a single variable, and they are very powerful to discover stages (i.e., changes of trend) when long monitoring periods are considered.…”

“…Actually, some authors set out the deployment of wireless sensors after analysing all the factors involved in restricting signal propagation and coverage [11,12]. More recently, the authors of this paper proposed installed multiple thermo-hygrometers in a library repository after conducting microclimate field campaigns in different time slots to study the horizontal and vertical distributions of temperature and mixing ratio of moist air [13].…”

Assessing the Impact of Climate Change on the Biodeterioration Risk in Historical Buildings of the Mediterranean Area: The State Archives of Palermo

“…In all these historical libraries including this case study investigated in this paper, the maximum annual indoor temperature exceeded 25 • C, beyond the safe threshold for chemical stability indicated in the standard [45]. Since the expected outdoor temperature increase will likely cause an increase in the indoor T, it becomes important to plan and implement right now adequate adaptation strategies to mitigate the risk of temperature-dependent deterioration and overheating in summertime [51]. In terms of the indoor relative humidity variations, the annual RH excursion experienced in Palermo is high compared to the RH stability (∆RH = 10%) occurring in the Archive of the University Library of Bologna and Palatina (Parma) but similar in magnitude (i.e., ∆RH = 35%) to the one reported in Ca' Granda and Malatestiana.…”

A Multidisciplinary Approach to the Evaluation of Air Quality and Thermo-Hygrometric Conditions for the Conservation of Heritage Manuscripts and Printed Materials in Historic Buildings: A Case Study of the Sala del Dottorato of the University of Perugia as a Model for Heritage Preservation and Occupants’ Comfort

“…In addition, unsuitable handling of books is frequently responsible for the accumulation of wear and tear on paper, thus reducing the durability of the collections. Moreover, since library materials can shrink/swell as they lose/gain moisture, fluctuations in temperature and relative humidity can be studied as mechanical stressors potentially inducing dimensional changes in library objects [13]. This phenomenon is particularly relevant in historical buildings, especially those not equipped with HVAC (Heating, Ventilation and Air Conditioning) systems or whose envelope is characterized by massive walls with vast hygrothermal inertia.…”