SSS 2012-04-17

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As it ages, white paper turns a distinctive¹ yellow. But why? To find out, scientists artificially aged² modern paper to reveal the changes on the molecular³ level. The research is in the journalPhysical Review Letters. 

 

For 48 days, three unbleached paper samples aged rapidly in reactors⁴ that simulated different environmental conditions. The researchers then compared the artificially aged samples to the real deal: three pieces of paper crafted in 15th-century Europe. This technique allowed them to gauge⁵ the types and amounts of changes going on.

 

About 90 percent of the weight of old paper is cellulose, the sturdy material that makes up plant cell walls. But over time cellulose fibers⁶ oxidize. The process modifies parts of various molecules⁷ and turns them into what are called chromophores, which absorb light.

 

White paper is white because it reflects all colors of light. Aging paper filled with chromophores reflects wavelengths⁸ that make it look yellow. The nondestructive technique used in this study could inform research to preserve and even whiten ancient texts and art. And give paper conservation a brighter outlook.

 

Thanks for the minute for Scientific Americans 60 second Science I am Sophie Bushwick~

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