Yellow Pages

[shazzabell]

Why do books pages 'yellow' over time?

[Buenchico]

See here:
http://en.wikipedia.org/wiki/Foxing

Chris

[Clanad]

While Buenchico's answer is nearly adequate as it relates to the subject of foxing that's not the cause of paper yellowing. Foxing, as the article states, is thought to be caused by mildew, primarily, and leaves unsightly spots and dark areas on paper. Whereas 'yellowing' of older documents is usually caused by the inferior paper being used. As you may have noticed, there are a lot of 'old' documents in museums and libraries that don't exhibit the yellowing. This is due to the fact that the chemicals used to break down wood particles to achieve a pulp for modern paper making include bisulfites, sulfides, sulfurous acid, sodium hydroxide, chlorine dioxide, and sulfates (Source Economic Botany). These acids are responsible for the majority of the yellowing. The older papers that don't yellow referenced above were made from rags and other cloth materials. Acid free paper is used for museum quality documents and is ruther expensive...

[shazzabell]

Interesting. Thank you very much.