As it ages, white paper turns a

As it ages, white paper turns a 1 yellow. But why? To find out, scientists artificially aged modern paper to reveal the changes on the molecular level. The research is in the journal Physical Review Letters. For 48 days, three unbleached paper 2 aged rapidly in reactors that simulated different environmental conditions. The researchers then compared the 3 aged samples to the real deal: three pieces of paper crafted in 15th century Europe. This 4 allowed them to gauge the types and amounts of changes going on. About 90 percent of the weight of old paper is cellulose, the sturdy 5 that makes up plant cell walls. But over time cellulose fibres oxidize. The process 6 parts of various molecules and turns them into what are called chromophores, which absorb light. White paper is white because it reflects all colours of light. Aging paper filled with chromophores reflects wavelengths that make it look yellow. The non destructive technique used in this study could inform research to 7 and even whiten ancient texts and art. And give paper conservation a brighter outlook.