Understanding Library Material Deterioration: Causes and Prevention

Walk into any old library and you will find books that crumble at the edges, pages stained yellow, and bindings that flake apart at a touch. This is not neglect alone. Every item on a library shelf is slowly breaking down from the moment it is created. For library professionals, understanding why materials deteriorate is the foundation of preservation work. The causes fall into clear categories, and once you know them, you can slow the decay considerably. This post walks through the internal, external, human, and digital threats that libraries face, with a focus on what can be done about each.

Internal factors: when materials destroy themselves 🔗

Some deterioration begins inside the material itself. Conservators call this inherent vice, the built-in chemical instability of the substances used to make books and documents. No matter how carefully you store such an item, it carries the seeds of its own decay.

Paper quality and acidity 🔗

Paper is the backbone of most collections, and not all paper is equal. Before the 19th century, paper was made from cotton and linen rags, which produced strong, stable sheets that survive for centuries. The Industrial Revolution changed this. To meet rising demand, manufacturers switched to wood pulp, which is cheaper but contains lignin, a compound that turns acidic as it oxidises. This acidity triggers the hydrolysis of cellulose, the process that makes pages turn brittle and brown.

The problem was worsened by sizing agents. From the 1830s onward, paper makers used alum-rosin sizing, which releases sulfate ions and protons that attack paper fibres over time. This is why many books printed between roughly 1850 and 1990 are in far worse shape than manuscripts that are several centuries older. Modern archival paper uses alkaline or neutral pH formulas and is often buffered, which dramatically extends its life.

Ink composition 🔗

Ink is another internal threat. Historical iron gall ink, widely used for centuries, contains acids and iron salts. Over time these can become corrosive and literally eat through the paper they sit on, a process known as ink corrosion. Affected documents develop holes exactly where the writing is heaviest, sometimes destroying the very text a library is trying to protect.

Leather and other bindings 🔗

Leather bindings are vulnerable too. Many leather covers from the 19th and 20th centuries suffer from red rot, a condition in which the leather degrades into a reddish powder and loses all strength. This is largely a result of the acidic chemicals used in tanning combined with exposure to pollutants. Adhesives, glues, and the gelatin in book spines are also organic and break down with age, causing pages to loosen and covers to separate.

External factors: the environment that surrounds the collection 🔗

Even materials made from the finest paper will not last if the environment is hostile. Environmental agents often do more visible damage than inherent vice, and they are also the factors a library can most directly control.

Light 🔗

Light is a form of electromagnetic radiation that damages materials in ways that cannot be reversed. Both visible light and invisible ultraviolet radiation cause fading of inks and dyes, yellowing of paper, and embrittlement of materials. A book left in a sunny window will fade and weaken far faster than one kept in a dim, controlled space. Libraries reduce this risk by filtering UV from windows and display cases, lowering light levels in storage areas, and keeping rare items away from direct sunlight. This is why exhibition rooms in museums and archives are often kept deliberately dark.

Temperature and humidity 🔗

Temperature and relative humidity are the two most important environmental factors, and they must be managed together. High temperatures speed up the chemical reactions that cause decay, roughly doubling the rate of acid deterioration with every significant rise. High humidity is even more dangerous, because it hastens acid breakdown and creates the damp conditions that mould needs to grow.

Fluctuation is its own threat. When temperature and humidity swing up and down, materials repeatedly expand and contract, setting up internal stresses that warp bindings and weaken paper. Conservation guidance generally recommends a stable temperature of around 18 to 20°C and relative humidity in the range of roughly 50 per cent, with the emphasis on minimising fluctuation. For libraries in tropical and monsoon climates, where heat and dampness are the norm for much of the year, this is a constant challenge that often requires air conditioning and dehumidifiers.

Pollutants 🔗

Airborne pollutants attack collections both from outside and within the building. They divide into two groups. Gaseous pollutants such as sulfur dioxide, nitrogen oxides, ozone, and formaldehyde react with paper and leather to form acids, accelerating chemical breakdown. Sulfur dioxide from burning fuel is a particular hazard in industrial cities, which is why collections in places like Mumbai or Kanpur face heavier pollution stress than those in cleaner areas. Particulate pollutants such as dust, soot, and grit abrade surfaces, disfigure pages, and attract insects. Good ventilation, regular cleaning, air filters, and storing books in closed cabinets all help reduce these effects.

Biological threats 🔗

Living organisms are among the most destructive agents in a library, especially in warm, humid regions. Biological deterioration and environmental damage are interconnected, because humid conditions favour fungal growth and accumulated dust attracts insects. The main culprits are:

Mould and mildew: These fungi thrive in damp, warm, poorly ventilated spaces. Once established they spread quickly, stain and weaken materials, and can also pose health risks to staff and readers. Keeping relative humidity below about 55 per cent is the single most effective defence.

Insects: Silverfish, booklice, cockroaches, and termites feed on paper, glue, and bindings. In tropical environments termites and cockroaches are especially damaging, boring through volumes and hollowing out spines.

Rodents: Rats and mice gnaw on paper and bindings for nesting material and leave droppings that stain and corrode.

Control depends on good housekeeping, controlled humidity, regular inspection, and integrated pest management rather than simply spraying chemicals, which can themselves harm materials.

Human factors: damage by people 🔗

People cause a surprising share of the damage in libraries, sometimes carelessly and sometimes deliberately.

Negligence by staff and users 🔗

Everyday handling takes a toll. Pulling a book by the top of its spine, forcing a volume to lie flat and cracking the binding, turning pages with dirty or oily hands, dog-earing corners, and using pens or sticky notes all shorten a book’s life. Poor shelving practices, such as packing volumes too tightly or leaving them to slump at angles, cause physical strain. Food and drink near collections invite both stains and pests. Staff negligence matters too: improper storage, failing to monitor the environment, mishandling during repairs, and applying unsuitable adhesives or tape can do lasting harm. Training both staff and readers in correct handling is one of the cheapest and most effective preservation measures available.

Vandalism and theft 🔗

Deliberate harm includes marking, highlighting, and writing in books, tearing out pages or plates, and slicing illustrations from rare volumes. Theft removes items from the collection entirely, and the loss of unique or rare material is permanent. Libraries respond with security systems, supervision of reading rooms, restricted access to rare collections, and careful records of holdings.

Digital data loss: a new kind of fragility 🔗

As collections move online, libraries face threats that paper never had. It is tempting to think digital files are permanent, but they are arguably more fragile than print. A well-made book can survive centuries with no intervention; a digital file can become unreadable within a decade.

Software and hardware obsolescence 🔗

The biggest digital threat is technological obsolescence. Formats, software, hardware, and storage media all become outdated as technology advances. A file may remain perfectly intact yet be inaccessible simply because no working software exists to open it. Anyone who has tried to read a floppy disk, a Zip drive, or an old proprietary word-processor file knows this problem. Older storage media stop being manufactured, the drives to read them disappear, and the data is effectively stranded.

Bit rot and media decay 🔗

Digital media physically degrade too, a process often called bit rot. Bit rot, failing storage media, and obsolete formats can compromise or destroy digital objects over time. CDs and DVDs deteriorate, hard drives fail, and the electromagnetic signals on tapes weaken. Files stored in only one place are especially at risk, since a single disk failure or server crash can wipe out a collection with no recourse.

Viruses and accidental erasure 🔗

Malicious software can corrupt or delete files, and ransomware can lock an entire collection. Human error is just as dangerous: accidental deletion, overwriting, formatting the wrong drive, or simply misplacing files all cause permanent loss. Even storing material with a cloud provider offers no guarantee, since files can still be deleted or corrupted and service terms rarely promise survival.

Digital preservation therefore demands active management rather than passive storage. Libraries rely on multiple backup copies kept in different locations, regular migration of files to current formats, integrity checks to detect corruption early, and the use of open, well-documented standards instead of proprietary ones. Institutions like the Library of Congress maintain dedicated programmes to keep digital heritage accessible across generations.

Bringing it together 🔗

Deterioration is rarely the result of a single cause. Acidic paper, high humidity, pollution, and careless handling reinforce one another, and the same is true in the digital world. Effective preservation starts with recognising every threat at once, controlling what can be controlled in the environment, training the people who use the collection, and planning actively for the long-term survival of both physical and digital materials.

What do you think? Which threat do you believe is most underestimated in libraries today, the slow chemical decay of paper or the silent obsolescence of digital files? And in your local climate, which environmental factor would be hardest to bring under control?

References

1. https://www.sciencedirect.com/science/article/abs/pii/S0165237008001964
2. https://www.nedcc.org/free-resources/preservation-leaflets/2.-the-environment/2.1-temperature,-relative-humidity,-light,-and-air-quality-basic-guidelines-for-preservation
3. https://greatlibraryexpectations.wordpress.com/2016/10/25/preservation-agents-of-deterioration/
4. https://cool.culturalheritage.org/byauth/maravilla/deterioration-causes.html
5. https://www.sciencedirect.com/topics/computer-science/digital-preservation
6. https://digitalpowrr.niu.edu/long-term-preservation-of-digital-objects/
7. https://www.loc.gov/programs/digital-collections-management/about-this-program/