Mould occurs in connection with unfavourable storage and/or water damage. Under certain conditions, e.g. warm, damp rooms, it can develop very quickly and almost completely destroy books in a short period of time. The mould can be treated using different methods, from brushing it off to irradiation, depending on the gravity of the situation. In serious cases a decontamination of the whole room may be necessary. An optimal storage place, in terms of temperature and humidity, prevents mould developing. In cases where parts of the books are lost, the disinfected objects will transferred back to their original state by the restorer.
In centuries gone by, ink was produced from oak apples and iron tinctures. When poorly stored – in humid rooms - the combination of these substances can react and release sulphuric acids, which in turn attack the paper or parchment, making the text disappear and creating holes. These objects have to be deacidified by a restorer. Loss of substance can then be treated by hand.
The penetration of liquid wears down the paper fibres and leads to discolouration. Damaged paper can easily become ripped, and so further damage often follows. A proper restoration of the objects can only be undertaken once an investigation has been made into possible consequential damage (e.g. mould, ink spots).
The effects of high humidity and high temperatures are the main factors behind damage to books and bound works. Alongside the natural deformation of objects due to changes in temperature and humidity, bacterial attacks and chemical reactions can also occur.