This Is Why Newspapers Turn Yellow Over Time

为什么报纸放久了会变黄

If you’ve ever stumbled across old newspapers, you might have noticed an interesting trend: Most of them are yellow—and no, they weren’t always that way. In short, this color-changing phenomenon is due to the process of oxidation. (In other words, the same process that turns a half-eaten apple brown.)

如果你偶然翻看旧报纸，你可能会注意到一个有趣的情形：大多数报纸都是黄色的，当然，它们并非一直如此。简而言之，这种变色现象是缘于氧化过程。（换句话说，这和只吃了一半的苹果会变成褐色是同样的过程。）

To break down this scientific process, let’s start with the basics. Paper is made from wood, and wood contains two substances called cellulose and lignin. When the chromophores (molecules responsible for color) found in lignin are exposed to air and sunlight, the lignin’s molecules become less stable and absorb a greater amount of light. In turn, the newspaper’s hue gradually darkens from white to yellow.

我们从其基础开始，来分解这个科学过程。纸是由木材制成的，木材含有两种物质，分别叫做纤维素和木质素。当木质素中发现的发色团（用于显色的分子）暴露在空气和阳光下时，木质素的分子就会变得不那么稳定，并吸收更多的光。紧接着，报纸的色调逐渐从白色变为黄色。

The reason newspapers are more prone to this color change, in comparison with other types of papers, is because the wood’s lignin isn’t typically filtered out. This both saves on the costs of mass daily printing and leaves the papers more prone to oxidation. (A chemical process called conservation bleaching can be used to produce yellow-resistant papers to avoid discoloration over time.)

与其他类型的纸张相比，报纸更容易出现这种颜色变化的原因是因为木材的木质素通常没有被过滤掉。这既节省了大量日常印刷的成本，又使纸张更容易氧化。（一种名为保护性漂白的化学过程可用于生产防氧化纸，以避免纸张随着时间的推移而变色。）

Fortunately, the lifespan of newspapers can be lengthened if they’re stored properly. The best way to preserve newspapers is to keep them out of sunlight and store them in acid-free and buffered boxes. Doing this allows the acids released by the papers to be neutralized by the alkaline buffers, helping the papers retain their white color.

当然有幸的是，如果报纸存放得当，它的使用寿命可以延长。保存报纸的最佳方法是让它们远离阳光，并将它们存放在无酸并有缓冲的盒子里。这样能使纸张释放的酸被碱性缓冲液中和，使纸张保持白色。

（翻译：MS小冰晶）