This is post #1 of #BlogchatterA2Z. This includes blogging everyday in April for 26 days, except on Sundays. What’s special about it is that every day’s post will be corresponding to each letter of the alphabet.
My theme for 2021 is Bookish Trivia. If you liked this post, don’t forget to “roll” me on Blogchatter’s website!
All my #BlogchatterA2Z posts 2021 can be found here.
Why do pages of books and newspapers turn yellow with age?
Adventure movies with treasure hunts always show yellowing, crumbling ancient scrolls, journals and maps.
This occurs due to a process called age tanning or browning. When it happens only on the edge of pages, it is called edge tanning.
It’s usually seen in books that were produced before acid-free paper with limited lignin arrived in the 1980s. The paper becomes brittle and loses substance quickly.
Tanning tends to start from the outer edges of books and moves inwards over time, thus creating a yellowish or brownish border on the pages.
The end papers of books are usually more acidic than the rest of the pages, so they undergo tanning faster. The process is more noticeable in the areas where glue has been applied to the back or where bookplates or newspaper cutouts have been kept.
Age tanning is used interchangeably with another term, foxing. But they are different phenomena. Foxing typically involves the work of fungus to create spots on the paper.
I’ll talk about foxing for “X” later in this A2Z series.
Why does it occur?
Blame it on oxygen.
Paper is made from wood, which is composed of two types of substances– cellulose and lignin.
Lignin makes the structure of plant cells sturdy and gives wood its rigidity and strength. That’s why trees can stand upright.
According to Dr. Hou-Min Chang of N.C. State University in Raleigh, without lignin, trees would grow to a height of only around 6 feet. Lignin also protects the wood from damage by pests and other factors.
Cellulose is a colorless substance that reflects light well, thus it is seen as white.
When lignin is exposed to light and oxygen in the air, it becomes oxidized i.e. it picks up the oxygen molecules and its structure changes to include regions called chromophores.
Chromophores (meaning color bearers or color carriers) cause lignin to look yellow or brown.
How is paper made?
Paper manufacturers attempt to remove as much lignin as possible by bleaching it via a chemical solvent process so that the paper looks white. The less the lignin content of paper, the longer it will resist age tanning.
That’s why newspapers turn yellow so quickly. They must be produced cheaply so manufacturers leave in more lignin that the paper in notebooks. In the paper mill, wood that will be converted to newsprint is ground up without bleaching out the lignin.
If newspapers were protected against sunlight and oxygen, they would remain white.
The stiffness of lignin is made use of in brown paper bags and cardboard cartons. These paper products do not undergo bleaching, so they have a typical dark brown color. They also have the strength to carry heavy groceries and other objects.
Keep a book in an air-tight container filled with an inert gas like argon and you could preserve it in pristine condition forever. Of course, it’s not always practical.
Paper degradation and oxidation constitute the worst nightmare of archivists and librarians. Although yellowed pages are sometimes considered charming by book collectors.
Preserving non-digitized documents of historical importance involves an understanding of the environmental agents that damage paper and speed up the oxidation process. Paper products must be protected from sunlight, air and moisture.
Processes to create tanning resistant paper were developed in the 1930s and standardized in the 1980s, so it’s less of a problem in modern books.
An Interesting Video on Age Tanning
Here’s a comprehensive video that explains age tanning: