Response to the question regarding pH-induced colour shifts in organic dyes on paper, posted by Fiona McLees in vol. 33 issue 28:
I was recently part of a research project focused on a photo album from the Tropenmuseum in Amsterdam, whose coloured album pages display intense local discolouration caused by contact with an alkaline adhesive. The album paper is of a dark, olive-grey colour and the areas damaged by the adhesive appear bright yellow-orange. The colourants in the paper were identified as synthetic dyes of the triarylmethane and azo classes. The damaging adhesive was identified as a mixture of starch with sodium silicate, a highly alkaline compound also known as waterglass. Although the research could not fully explain the discolouration, it seems like the high pH of the damaging adhesive mostly affected the triarylmethane dyes, while the azo dyes underwent only minor changes. Triarylmethane dyes are known to shift colour depending on pH conditions. In aqueous media, these colour shifts are theoretically reversible, but it's not clear what happens when these dyes are used on paper and how the substrate affects the discolouration process. It's great to hear of new studies looking into pH-induced colour changes on paper! I would be happy to send more information on my research to anyone interested in this topic. Andra Danila Paper Conservator in Training University of Amsterdam [email protected] ****** Unsubscribe by sending a message to [email protected] Searchable archives: http://cool.conservation-us.org/byform/mailing-lists/cdl/
