Degradation, remediation and protection of library materials

The broad term 'library materials' encompasses a vast range of objects produced by humans over a long period of time and destined for a great variety of uses and expressive aims. They include animal skins, palm leaves, papyrus stems, split bamboo, textiles and practically any support that offers a surface suitable for writing (Bloom, 2017). The invention of paper in 105 A.D., announced by Cai Lun to the Chinese emperor Ho-ti of the Eastern Han dynasty, initiated the establishment of libraries as we know them today, namely places where books are kept, organised and used. However, paper and its widespread use developed quite slowly, hence most of the oldest surviving manuscripts are supported by other materials, parchment in particular (Bloom, 2017). We can therefore say that most of the manuscripts, books and archival documents that have come down to us today are predominantly made of paper or parchment, and sometimes both. Different types of ink were used to write them, and they often incorporate protective and ornamental elements such as pigments, wood, textiles, leather and metals. The study of microorganisms that cause paper and parchment biodeterioration probably began with the generation of microbiologists to which Christian Gottfried Ehrenberg (1795-1876) belonged (Williams et Huxley, 1998). Ehrenberg was a German naturalist and microscopist; he was the first to isolate and describe microfungal species using paper as growth substrate. For example, the fungus Chaetomium chartarum, named by Ehrenberg in 1818, is a cellulolytic fungal species that typically degrades cellulosic substrates, including paper (charta in Latin) (Figure 1). Later, other scholars focused on the study of paper biodeterioration at a time when the rigour of attributing a cause to an effect, summarised by Kock's postulates (Grimes, 2006), pervaded all areas of microbiology, even those in which the 'patient' was non-living matter such as paper or leather. Koch's postulates consist of four criteria intended to establish a causative relationship between a microbe and a disease: 1) the microorganism must be present in every case of the 'disease'; 2) it must be isolated from the host presenting with the disease and grown in pure culture; 3) the specific disease must be reproduced when a pure culture of the bacteria is inoculated into a healthy susceptible host; 4) the microorganism must be re-isolated from the inoculated, diseased experimental host and identified as identical to the original specific causative agent. The postulates were published by Koch in 1890 to describe the aetiology of cholera and tuberculosis and were subsequently applied to other diseases. From the 1920s onwards, and for at least 60 years of library materials' microbiology thereafter, the study of biodeterioration was based on the belief that for every type of damage there was a specific culprit, and in many investigations authors strenuously sought to refer to Kock's postulates to prove that isolated organisms were the real cause of the observed damage. This approach has sometimes worked, but not always. In 1997 Zyska reviewed the list of filamentous fungi associated with library materials' biodeterioration and found that 234 species belonging to 84 genera were isolated between 1919 and 1977 from a range of materials, not only paper or parchment (Zyska, 1997), and stressed how most of these organisms were also present in the air of Polish archives. He also lamented the lack of interest in isolating library materials bio-deteriorating organisms by culture in collections worldwide. As a matter of fact, the importance of controlling environmental conditions in preventing biodeterioration was recognised early on as the first, if not the only weapon against damage-causing phenomena, in con