One of the things I worked on so far this summer is a pamphlet from 1851. The paper around the text is discolored to a dark brown! This is because the ink it was printed with had too much oil in it. Over time, the oil spread out into the surrounding paper and caused it to brown. It also made the paper more brittle, while the paper in the margins remains white and strong. These photos were taken after treatment which included humidifying and flattening the corners of some of the pages and mending tears, most of which were in the darkened portion of the paper.

Front of pamphlet

Front of the pamphlet

Interior of pamphlet

Interior of the pamphlet

detail of a repair

A detail of one of the repairs.  It really is there, but since the paper is so thin I was able to use a thin repair tissue, making the repair really hard to see.