Books disclose their age with their appearance, as do we humans. Whether you’re a bibliophile or a biblio-phobe, most of us agree that yellowing of book pages is an authenticated and vintage outlook of books. However, do you know why book pages turn yellow over time?
Book pages turn yellow over time due to a slow chemical reaction inside the page molecules. The natural plant material used to make paper contains lignin. This chemical reacts with oxygen and turns yellow over time. Hence, the books appear yellow or brownish, especially when exposed to open air.
The remainder of this article will discuss the cause of yellowing papers in greater detail. It will also cover how long it takes for a paper to get yellow, whether we can prevent books from turning yellow, and if so, how. Furthermore, we’ll tell you how to remove yellowness from antique books.
Paper is made of plant fibers called cellulose. Paper manufacturers collect cellulose fiber from trees and make pulp out of it. Then the pulp is processed and converted into a paper sheet. Cellulose is colorless and a good reflector of most of the wavelengths of light. That’s why our eyes perceive paper as white.
Along with cellulose, the natural plant fibers also contain a chemical component called lignin. Lignin changes its color in the process of oxidation. Hence it’s responsible for the change in color of book pages or any paper products.
Lignins are a type of organic polymer. They give structure to the plant cells by forming cell walls. The stiffness of the paper is due to the presence of lignin, and it’s crucial to provide the paper with the strength it requires.
However, this crucial component also has a drawback: it changes color over time and gives pages a golden-yellow tinge. Hypothetically, if there’s no lignin in the paper contents, it wouldn’t turn yellow. However, paper can lose some of its original colors and shine in the process of degradation.
The papers with a higher percentage of lignin get yellow faster than those with less lignin. Weathering conditions and state of preservation also play a huge role, and they can accelerate or hinder the oxidation process of lignin.
The manufacturers try to remove lignin from the plant fibers as much as possible to prevent the rapid yellowing of books and notebook pages. On the other hand, some papers need higher lignin content to hold firm. Carry bags, paper bags, cartons, cards, hardcovers, etc., are examples of high lignin-containing papers.
The process of yellowing books is dependent on several factors. We can’t determine the exact time a book will turn noticeably yellow.
It takes about five to six years for books with average lignin levels to noticeably turn yellow, assuming they have been stored in average preserving conditions. However, defining the average conditions for all contributing factors isn’t easy.
Here are some factors that contribute to the yellowing process:
As we discussed earlier, the amount of lignin in the paper ingredients is directly proportional to the darkness of color and the speed of yellowing of paper. The excellent quality paper goes through an intense bleaching process to minimize the lignin content.
On the other hand, lousy quality paper, cardboard, and hardcovers contain more lignin and are more susceptible to degradation.
Humidity is a crucial weathering component that needs to be balanced. Unlike lignin content, humidity is required for better preservation of books. If the book is stored in too dry climatic conditions, pages will become brittle and prone to cracking.
On the other hand, too much humidity can also harm the paper. Pages can develop fungus or mold if the environment contains too much water vapor. The ideal conditions are 40-50% RH (Relative Humidity).
Temperature works as a catalyst in the lignin oxidation process. Hence there should be a balance for better preservation. Moreover, the fluctuations in temperature can be more harmful to the yellowing and the overall deterioration of paper.
According to the Art Institute of Chicago, 68 – 72 ºF (20 – 22.22 ºC) is the ideal temperature for preserving books.
All kinds of light that include UV radiation are harmful to the books, including sunlight and fluorescent lights. It speeds up the yellowing process and lignin oxidation.
It would be best if you store books in a dark place. If possible, it’s best to use UV filters and keep lights off when not required. Needless to say that direct sunlight will yellow down the books faster.
As books age, they off-gas several chemicals in the form of gas. Off-gassing itself is the indication of deterioration. Moreover, it stimulates the degradation of other books.
Good airflow and spacing between the bookshelves can lessen the effect of chemicals released in off-gassing.
Yellowing is like the slow death of the books. Books turn yellow and eventually brown when they degrade. It’s a natural process. The degradation process can take several generations if the preserving conditions are good before the book decomposes completely.
Technically, it’s impossible to prevent the yellowing of books. However, you can slow down the process of degradation that’ll result in delayed yellowing. Factors that need to be kept in mind are heat, humidity, air circulation, and direct sunlight. All of them negatively affect the paper.
The best way to avoid degradation is to prevent it in the first place. For that, you need to control the factors mentioned above. Moreover, there are some ways to restore the books that have already been affected.
Hydrogen peroxide treatment, UV filters, microchamber interleaving paper, and bleaching are the most famous ways to extend the shelf life of books. It’s best to treat acidity as it’s one of the biggest enemies of organic compounds.
If you keep in mind a few things that affect the books negatively, it won’t be challenging to preserve your books better for more extended periods and slow down yellowing.
You can follow the given things to prevent your books from yellowing:
- Keep books away from direct sunlight. It speeds up the process of lignin oxidation.
- Turn indoor lights off when inessential. Fluorescent lights also emit UV rays that harm books.
- Maintain moderate humidity. Optimal humidity is crucial for the longevity of the paper. A too dry or humid environment can damage the books beyond repair.
- Keep the temperature stable. When the temperature fluctuates, it negatively impacts the paper and stimulates disintegration faster.
- Ensure good air circulation. Good air circulation is essential to keep the effect of off-gassing minimal.
- Don’t keep books underground. The temperature fluctuates more underground; hence, these kinds of places should be avoided to ensure the health of the books.
- Don’t place the bookshelf next to a window. Like underground spaces, places near a window are more prone to heat during the day and cool during the nights. This regular temperature fluctuation is a recipe for disaster for papers.
- Keep the VOCs lower around the books. Volatile Organic Compounds (VOCs) are chemical vapors present everywhere. They’re considered a pollutant and unhealthy for preserved goods, including paper products.
- Use a metal or sealed wood bookcase. Unsealed wooden bookcases off-gas chemicals. Hence metal is best to use. Or seal the wood before using it as a bookcase.
- Put lining paper on the shelf before keeping books on it. It’ll protect against off-gassing.
- Separate new books from old ones. Already yellowed books emit chemicals; hence, they should be separated from new ones to prevent yellowing.
- Keep space in between the bookcases. It’ll ensure air circulation and keep books less affected by off-gassing.
- Preserve antique books in inert gasses like argon or helium. That doesn’t apply to every book you have in your collection. Instead, the one that’s antique and needs longer preservation. Oxygen is the enemy of the books as it oxidizes lignin.
- Restore books from time to time. Restoration of books gives them a new life, and old books survive longer if they get treatment on time.
- Use UV filters. UV filters might be costly. However, if you’re committed to your books, you may not want to leave any stone unturned. Applying UV filters will save the papers from UV rays emitted by the sun or artificial lights.
- Put microchamber interleaving paper under the book pages. It’s a thin paper sheet that absorbs chemicals like a sponge.
You can prevent or delay yellowing by doing the things mentioned above. However, what if your book already has passed the prevention limit and needs severe treatment? Don’t worry. We have several methods to remove the yellow color from books.
Here are five ways to treat yellowed books:
Microchamber interleaving paper is a thin paper made of 100% cotton. This product is designed to absorb acid removed from paper as a byproduct of deterioration.
The paper uses zeolite molecular trap technology to absorb off-gassed chemicals and other byproducts. It’s used extensively by the conservators as the most reliable product for the conservation of the books.
The product comes in a package of 100 sheets. You need to put a thin sheet between book pages, and it’ll do the rest of the work. Microchamber interleaving paper can take some time to do its magic. So, be patient with it.
Hydrogen peroxide can remove oxidation marks, yellow patches of foxing, mold, and other stains from the paper. However, you need to be very cautious while using it on your precious books as it can further damage paper if not used correctly.
Things you’ll need:
- Diluted hydrogen peroxide (not more than 10% concentration)
- Soft brush
- Cotton balls
Follow the steps below to remove yellow stains from books:
- Apply the hydrogen peroxide gently on the affected area with the help of a brush. Don’t repeat the strokes on the same spot.
- Dab the cotton ball on the applied area to soak the excess solution from the paper.
- Wait until the page dries completely. Please don’t keep the paper in the sunlight to dry it out.
- Follow the same steps on the next page.
Sandpaper is best to clean the edges of the book. However, you shouldn’t use sandpaper on the page where it’s printed as it’ll fade out the ink or tear the page. Moreover, while rubbing sandpaper on the side edges, hold the book tight and intact. Otherwise, pages can tear.
Things you’ll need:
- 220-320 grit sandpaper
- Dusting brush
Follow the steps below to clean the yellowed and dirty edged books:
- Cut out a small portion of sandpaper.
- Hold the book tightly and rub the sandpaper on the edges. Don’t use back and forth strokes. Instead, rub the sandpaper only in one direction.
- Brush off the fine dust removed from the books.
Paper manufacturers use chlorine to bleach the pulp before producing the paper to remove lignin. However, you can use chlorine bleach later to revert the signs of deterioration. It’s safe for both the paper and the conservator.
Things you’ll need:
- Chlorine bleach (5% concentration)
- Distilled water
Follow the steps below to bleach the yellow paper:
- Lay down the paper in the tray.
- Pour distilled water and let the paper soak it.
- Remove the water from the tray.
- Pour diluted chlorine bleach
- Let it sit for a couple of minutes.
- Remove the chlorine water from the tray
- Once again, clean with distilled water.
- Dry out the paper.
You can use vinegar (75% concentration) in place of chlorine/household bleach.
Sodium bicarbonate is a basic chemical compound that can remove acid from celluloid items. You can follow the step-by-step guide below to remove yellow acid marks from the book pages with the help of power sodium bicarbonate (baking soda):
- Evenly sprinkle bicarbonate of soda on the affected area of the book page.
- Let it sit for a couple of hours.
- Dust it off with a cleaning brush.
You can also apply hydrogen peroxide before the baking soda. Keep in mind that this method can further damage the paper. Hence, don’t use this method on antique books that are important for you. It’s best to take your book to the professional conservator.
Yellowing of the books is a natural process of deterioration. Cellulose fibers that are initially colorless turn yellow over time. Moreover, one other component, lignin, oxidizes and eventually makes paper yellow and brownish.
No prevention method can completely stop the yellowing process of books. However, with the help of some preservation methods, we can delay the process and revert the coloration of books to some extent.
- EPA: Paper Making and Recycling
- Wikipedia: Cellulose
- Wikipedia: Lignin
- The University of Chicago Library: Caring for Your Books
- Art Institute Chicago: Appraisal and Preservation Resources for Books
- Biblio Blog: Tips for reducing your book collection’s exposure to the harmful effects of UV light and radiation
- Wikipedia: Volatile organic compound
- Cool.culturalheritage.org: Zeolite Molecular Traps And Their Use In Preventative Conservation
- Bookriot.com: How to Clean Books: Remove Stains, Mold, and Dirt From Old Books.
- Google Parents: Method to remove foxing stains from paper & celluloid items
- Wikipedia: Sodium bicarbonate