The first page of a book that has become acidic and yellowed from the book board. An inserted note protected a small square of the page, where it remains its original color - Anna Blackman, The University of Otago

The back of an ink drawing. The paper has become acidic over time due to contact with an acidic backing board. Areas covered in ink (which is basic) were protected and remain close to the original color - South Florida Art Conservation

A book that has been discolored by a piece of newspaper pressed between the pages - Emma Moesswilde