Why does paper go yellow over time?

Asked by: Karen Haines, Durham

Paper made from wood pulp contains lignin. This is a structural protein that’s responsible for most of the strength of wood. Lignin oxidises quite easily in air to a yellow or brown colour. Newsprint contains a lot of lignin and goes yellow fastest. Higher-grade paper is chemically treated to remove most of the lignin and also bleached, but a little lignin usually remains.

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