Panduran pen

Since the 19th century machine-made paper and board material was generally sized with alum. This has been the main reason for the premature decay of paper. Panduran is an eriochrome dye which reacts chemically to the aluminium ions present in alum, and in the process changes from yellow to blue to violet, thus detecting the alum content in the paper being tested. This reaction is not influenced by the pH value of the tested paper. Boards and papers with alum content are principally not suitable for long-term archival storage.