Understanding the Deterioration of Library Materials: Causes and Effects

Every book, manuscript, and newspaper in a library is quietly fighting a losing battle against time. Paper yellows, bindings crack, ink fades, and pages turn brittle enough to crumble at a touch. This decline is called deterioration, and it is not random. It follows clear scientific patterns driven by the materials themselves, the surrounding environment, and the people who handle them. Understanding why library materials break down is the first step toward slowing the process. This post breaks down the major causes of deterioration and explains what each one means for the collections we are trying to protect.

What deterioration really means 🔗

Deterioration is the loss of quality in a library material that reduces its ability to serve its purpose. The signs are familiar to anyone who has handled an old book: brittleness, cracking, discoloration, shrinkage, holes, and the steady accumulation of dust and dirt. These effects are usually gradual, cumulative, and irreversible. You rarely notice damage on a single day, but over years the changes add up until a document can no longer be read or even safely opened.

Almost every traditional library material is organic in nature. Paper, leather, parchment, and the glues that hold books together all come from plant or animal sources, which means they are chemically active and prone to breaking down. Conservators generally sort the causes of this breakdown into two broad groups: inherent causes built into the material itself, and external causes coming from the environment and from human handling. The reality is that these factors rarely act alone. They feed into one another, with environmental conditions often accelerating problems that were already present in the material.

Inherent causes of deterioration 🔗

Some materials begin decaying the moment they are made, simply because of what they are made from. This built-in vulnerability is known in conservation practice as inherent vice, the tendency of an object to deteriorate due to the fundamental instability of its own components rather than any outside force. The single most important inherent factor for library collections is the chemistry of the paper.

Cellulose, lignin, and acidity 🔗

Paper is essentially a web of cellulose fibres. Pure cellulose is reasonably stable, but the problem lies in what comes along with it. When paper is made from wood pulp, it contains lignin, a complex organic substance that gives trees their rigidity. Lignin is the villain of the story. As paper ages, lignin releases acid that degrades the cellulose, causing the sheet to weaken, turn yellow or brown, and eventually disintegrate. This slow self-destruction is sometimes called the “slow fire” of acidic paper.

The amount of lignin depends on how the pulp is processed. Mechanical pulping simply grinds wood into fibre and leaves most of the lignin behind, which is why low-cost products like newsprint are highly acidic and deteriorate rapidly, often flaking or shattering when handled. Chemical pulping, by contrast, removes most of the lignin, yielding stronger and longer-lasting paper. Fibre source matters too: lignin makes up 20 to 30 percent of wood but only about 1 percent of cotton, which is why cotton-based papers last far longer than wood-pulp papers.

Handmade paper versus machine-made paper 🔗

The shift from handmade to machine-made paper marks a turning point in the history of book longevity. For centuries, paper was made by hand, sheet by sheet, from rags and plant fibres like cotton, hemp, and straw. These long-fibre, low-lignin sheets were durable and naturally close to neutral in acidity. Many handmade documents from earlier centuries have survived in remarkably good condition.

That changed in the second half of the 19th century. As demand for newspapers and affordable books exploded, manufacturers turned to wood-pulp paper produced cheaply by machine. This made reading material widely available, but at a hidden cost. The acidic, lignin-rich wood pulp meant that books printed from the late 1800s onward were chemically programmed to decay. It was a librarian-chemist, William Barrow, who in the mid-20th century documented just how severely acidic paper was crumbling on library shelves, sparking the modern push toward acid-free and permanent paper. Today, paper meeting standards such as ISO 9706 can last several hundred years, while the best alkaline paper has a life expectancy of over a thousand years.

Inks, adhesives, and other built-in weaknesses 🔗

The paper is not the only inherent risk. Iron gall ink, widely used in manuscripts from roughly the 5th to the 19th century, contains iron sulphate and gallic acid that can turn corrosive over time and literally eat through the page, a process known as ink corrosion. Leather bindings can suffer “red rot,” where the leather turns powdery and disintegrates, a problem especially common in books from the late 19th and early 20th centuries due to changes in tanning methods. Adhesives add further vulnerability: animal-based glues attract pests, while some synthetic adhesives grow brittle or sticky with age, weakening the structure of a bound volume from the inside.

External causes of deterioration 🔗

Even a chemically sound book will not survive in a hostile environment. External causes include temperature, humidity, light, air pollution, pests, and natural disasters such as fire and flood. For Indian collections, these factors are especially demanding because much of the country combines high heat with high humidity for large parts of the year.

Temperature 🔗

Heat is an accelerator. Temperature is a measure of how fast molecules vibrate, and the warmer it gets, the faster the chemical reactions that break down paper proceed. As a rough guide, every rise in temperature speeds up acid deterioration. Equally damaging are rapid swings, because materials expand and contract with each change, setting up internal stresses that weaken fibres and crack bindings over time. Most preservation guidance recommends keeping paper-based collections cool and stable; the Smithsonian Institution Archives suggests a standard of roughly 35 to 65°F with controlled humidity for paper.

Humidity 🔗

Relative humidity may be the single most critical environmental factor, and it is the toughest challenge in India’s climate. Paper is hygroscopic, meaning it constantly absorbs and releases moisture from the surrounding air. When humidity is too high, it speeds up acid hydrolysis and, more dangerously, invites mould to grow on the glue, leather, and paper that feed it. A grey, dusty bloom appearing on bindings is an early warning that the air is too damp. When humidity is too low, paper dries out, shrinks, and becomes brittle. The general target for book storage falls in the range of roughly 30 to 55 percent relative humidity, with stability mattering as much as the exact number. Rapid daily or weekly fluctuations can cause significant damage on their own.

Light and air pollution 🔗

Light, especially the ultraviolet (UV) portion of sunlight and fluorescent lighting, is highly destructive. UV radiation causes inks to fade, paper and fabrics to discolour, and any lignin present to react and turn yellow or brown. The damage is cumulative and permanent, so a document left in direct sunlight will steadily lose both its text and its strength. Air pollution adds another layer of harm. In industrial cities, acidic gases and particulate matter settle on collections, accelerating chemical breakdown. Dust is not just dirty; it is abrasive, attracts pests, and holds moisture against the page. Reducing direct light, using UV-filtering glass on display cases, and keeping collections clean all help slow these effects.

Biological agents and disasters 🔗

Because library materials are organic, they are food for living things. Insects and rodents are drawn to the cellulose, starches, and proteins in paper, glue, and sizing. Termites, silverfish, and bookworms can reduce a volume to a network of holes or destroy it entirely, with the damage depending heavily on how quickly an infestation is caught. On top of these slow threats, sudden disasters such as fires, floods, plumbing failures, and roof leaks can wipe out parts of a collection in moments. India’s monsoon season and occasional flooding make disaster preparedness a real concern for many libraries.

Human factors in deterioration 🔗

People are part of every library, and people cause a large share of the wear and tear. The damage ranges from honest accident to deliberate harm.

Everyday handling does steady, often invisible harm. Turning pages with dirty or oily hands transfers grime and acids onto the paper. Forcing a tightly bound book flat at the spine cracks the binding. Dog-earing page corners, the practice of folding a corner to mark a place, creates a permanent weak line where the paper will eventually fracture. Resting open books face down, overstuffing shelves, pulling a volume off the shelf by the top of its spine, and writing or highlighting in margins all add up over a collection’s lifetime.

Both users and staff contribute. A reader photocopying a tightly bound volume can break its spine; a staff member shelving books too tightly or carrying too many at once causes physical strain on the materials. More serious human causes include theft and vandalism, which can mean stealing rare items or tearing pages out of books, and even improper repair, where well-meaning fixes using ordinary cellophane tape leave acidic, staining residue that does more long-term damage than the original problem. It is worth noting that for most everyday paper handling, clean dry hands are preferred; cotton or nitrile gloves are generally reserved for photographs rather than recommended for brittle paper, where they can reduce grip and increase the risk of tearing.

Preservation implications 🔗

Recognising these causes points directly to what libraries can do about them. The most cost-effective approach is preventive: controlling the environment and improving handling so that deterioration is slowed before it starts, rather than paying for expensive repairs later. Maintaining a cool, stable temperature, keeping humidity in a safe and steady range, blocking UV light, controlling dust and pests, and storing books upright with proper support together address most external causes. Choosing acid-free, permanent paper for new records and, where needed, deacidifying valuable acidic documents tackles the inherent chemistry problem.

India has built institutional muscle around exactly these challenges. The National Mission for Manuscripts, launched in 2003 and now restructured under the Gyan Bharatam Mission, works to document, digitise, and conserve the country’s vast manuscript heritage, with a strong emphasis on indigenous conservation methods suited to local conditions. It collaborates closely with the National Research Laboratory for Conservation of Cultural Property (NRLC) in Lucknow, which monitors temperature, humidity, light, and pollution in collections and trains conservators across the country. For library professionals, the practical takeaways are straightforward: handle materials gently, control the storage environment, educate users, catch infestations early, and prioritise prevention over cure.

What do you think? Looking at the books and documents around you, which cause of deterioration do you think is doing the most quiet damage right now? And what is one simple change in handling or storage that could meaningfully extend the life of the materials you use most often?

References

1. https://en.wikipedia.org/wiki/Inherent_vice
2. https://en.wikipedia.org/wiki/Wood-free_paper
3. https://psap.library.illinois.edu/collection-id-guide/paper
4. https://www.trueart.info/paper
5. https://en.wikipedia.org/wiki/Acid-free_paper
6. https://siarchives.si.edu/what-we-do/preservation/environment
7. https://ruuvi.com/monitoring-humidity-and-temperature-in-a-library/
8. https://cool.culturalheritage.org/byauth/maravilla/deterioration-causes.html
9. https://libguides.colorado.edu/PersonalArchiving/Books
10. https://www.namami.gov.in/research
11. https://cultureandheritage.org/2024/03/unveiling-the-national-research-laboratory-for-conservation-of-cultural-property-nrlc-safeguarding-our-heritage-for-future-generations.html