Latent Acidification of Books Composed of Alkaline Text Papers

Abstract The current study conducted in March–April 2021 elucidated the acidification process of books using alkaline text paper and improved the method of pH measurement in a previous study from 2016. The pH was measured on various positions of Japanese books published in 2000–2020 using the same type of pH-indicator strip as used in 2016; however, a wetted pH-indicator strip was kept pressed to the text paper with fingers at approximately 5 kgf for 90 s to secure the transfer of water-extracted components for four times while a 250 g paperweight was mounted and kept for 60 s for two times in the 2016-study. This time, the pH was found to decrease faster in positions more readily exposed to outside air compared to the 2016-study. Immediately after publication of the book, the pH was approximately 7.8 in every position. The pH of the top edge corner and the surface near the top edge corner later decreased to a neutral pH 7.0 4–6 years and 7–9 years after publication, respectively. Approximately 20 years after publication, the centre of the page in the interior of the book also dropped to pH 7.1, suggesting that acidification steadily progressed, albeit slightly, even on alkaline paper.