When we were kids, there was that day when our parents let us have a look at a dusty collection of historic old, yellowed newspapers. The Moon landing, political victories that started the great history of our own country and many more pillars of history, now sitting on bookshelves or hidden in trunks. These newspapers are fascinating artifacts documenting history, from remarkable moments to daily news. Unfortunately, these ancient relics are so hard to read due to the yellowed, brown color and fading print. So one day I asked myself: why does this happen? Is there any way to prevent this from happening?
Let’s start with the invention of paper. It’s thought that paper was invented around 100 BC in China. Originally made from wet hemp that was, then, replaced with pulp, tree bark, bamboo and other plant fibers. Paper soon spread across Asia, first only being used for official and important documents, but as the process became more efficient and cheaper, it became far more common.
Paper arrived in Europe around the 11th century. Historians believe the oldest known paper document from the European country is the “Missal of Silos” from Spain. The paper of this document was made out of a form of linen, the rest completely out of parchment. While paper, books, and printing would evolve throughout the next eight hundred years, with the Gutenberg printing press coming in the mid-15th century, paper was normally made out of linen, ragweed, cotton or other plant fibers. This until the mid-19th century when paper was made out of wood fiber.
So what changed during time? In 1844, two individuals invented the wood paper-making process.
On one end of the Atlantic Ocean was Canadian inventor Charles Fenerty. Growing up, his family owned a series of lumber mills in Nova Scotia. Knowing the durability, cheapness, and availability of wood, he realized it could be a good substitute for the much more expensive cotton paper, widely used all over his town . He experimented with wood pulp and, on October 26, 1844, he sent his wood pulp paper to Halifax’s top newspaper, The Acadian Recorder, with a note claiming the durability and cost-effective spruce wood paper. Since then, the Recorder used Fenerty’s wood pulp paper.
At the same time, German binder and weaver Friedrich Gottlob Keller was working on a wood-cutting machine when he discovered the same thing as Fenerty – that wood pulp could act as a cheaper paper than cotton. He produced a sample and, in 1845, received a German patent for it. In fact, some historians credit Keller for the invention more than Fenerty simply due to the fact that he received a patent and the Canadian didn't.
Within thirty years, wood pulp paper was used all over the world, but a little issue was very annoying. While wood pulp paper was cheaper and just as durable as cotton or other linen papers, there were drawbacks. Mainly, wood pulp paper is much more prone to being effected by oxygen and sunlight.
Wood is primarily made up of two polymer substances – cellulose and lignin.
Cellulose is a complex carbohydrate and one of the most abundant organic materials in nature. It is also technically colorless and reflects light extremely well rather than absorbing it, which would make it opaque. Therefore humans see cellulose as white. However, cellulose is also somewhat susceptible to oxidation, although not nearly as much as lignin. Oxidation causes a loss of electrons and weakens the material. In the case of cellulose, this can result in some light being absorbed, making the wood pulp of which paper is made appear duller and less white. But this isn't the cause of the yellowing in aged paper.
Lignin is the other prominent substance found in paper- in newspapers in particular. Lignin is a compound found in wood that actually strengthen the wood, making it harder. In fact, according to Dr. Hou-Min Chang of North Carolina State University in Raleigh:
Without lignin, a tree could only grow to about 6 ft. tall
Essentially, lignin functions as a sort of glue that binds the cellulose fibers, helping make the tree much stiffer and able to stand taller than it otherwise would, as well able to resist external pressures like wind.
Lignin is a dark color naturally and so it is highly susceptible to oxidation. Exposure to oxygen - especially when combined with sunlight - alters the molecular structure of lignin, causing a change in how the compound absorbs and reflects light. The result in the paper containing oxidized lignin is a yellow-brown color in the human visual spectrum.
Since the newspapers are made with a less intensive and cheaper process – in fact a lot of the wood pulp paper is needed – the paper used for it has significantly more lignin than the one for books, where a bleaching process is used to remove much of the lignin. So, as newspapers get older and are exposed to more oxygen, they turn a yellowish-brown color relatively quickly.
Thanks to the bleaching process, the paper used in the production of books tends to be of a higher grade and the oxidation doesn't happen so quickly. However, the chemicals used in the bleaching process to make white paper modifies the cellulose formula, making it more susceptible to oxidation than it would otherwise be.
Paradoxically, the process of paper whitening slightly contributes to the yellowing of the pages during time.
Nowadays, against this, many important documents are now written on acid-free paper with a limited amount of lignin, to prevent it from deteriorating over a long period of time.
As for old historic documents – the one already destroyed by time – there may not be a way to reverse the damage already done. But few simple rules can prevent further damage. As the historians taught us, it is essential to store the documents in a cool, dry, dark place, just like how museums store historic documents in a temperature-controlled room with low-lighting. Also, you shouldn't store them in an attic or basement because those places can get humid and have temperature swings. Most importantly, limit the handling of these documents. Nothing destroys a valuable piece of paper like frequent handling. Also an UV protected glass could be an idea, but maybe this solution is not very cheap.
There’s no denying the yellowing of pages is connected with the unceasing flow of time. Watching such objects becoming old is such a fantastic process. Time exists and this is the proof.