SSS 2012-04-20（在线收听）

As it ages, white paper turns distinctive of yellow, but why? To find out, scientists artificially aged modern paper to rebuild the changes on the molecular level, the researchers in the Journal physical review of letters, for 48 days, 3 unpleached paper samples aged rapidly on reactors that's simulated in different environmental conditions, the researchers then compared the artificially aged samples to the real deal, 3 pieces of paper crafted in 15 century Europe, this technique allowed them to gauge the types and the months of changes going on, about 90% of the weight of old paper is cellulose, the sturdy material that makes plants so walls, but over time cellulose fibers oxidase, the process modifies parts of burriest molecules and turns them into what we call chromophores which absorb light, white paper is white because it reflect all colors of lights, aging paper filled with chromophores reflects wavelength that makes it look yellow, the non-destructive technique used in the study couldn't inform research to preserve and even widen in ancient * art and give paper conservation a brighter outlook.