A preliminary investigation into the low washfastness of indigo carmine during wet cleaning

Abstract

This research sought a basic level of understanding of the variability exhibited by indigo carmine during conservation wet cleaning, by studying its inherent properties. Thus far, causes and mechanisms behind indigo carmine bleeding have been minimally explained in published literature.
A methodological approach was adopted to answer whether the dye’s low washfastness showed variations according to dyeing conditions and formulations. Historical dye recipes were critically reviewed to find trends in use and manufacture. After identifying relevant variables in preparation and dyeing methods, different formulations of indigo carmine were recreated. Dye transfer and solubilisation for replica wool samples were experimentally assessed by visual examination and colourimetry. For the first time, a relationship between the lightfastness and washfastness of indigo carmine was identified, showing the impact of numerous interconnected factors on the dye’s wet-behaviour. Further experimentation with historical samplers allowed for comparison between theoretical arguments and expectations from practical conservation experience.
This research contributed to the understanding of the historical and technological context of indigo carmine production. It concluded that assumptions about the dye’s properties have led to an overly simplistic view of its behaviour during wet cleaning. Informed decision-making is needed, balancing the benefits of wet cleaning against the likelihood of dye loss and colour change.