Why does paper go yellow over time?
Paper made from wood pulp contains the structural protein lignin which oxidises easily in air.
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.
Subscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun science facts.
