Colour change tools to assess Honey Syndrome and Vinegar Syndrome in motion picture films

Motion picture films with support in cellulose nitrate or cellulose triacetate are extremely vulnerable. Deterioration is mainly attributed to the depolymerization of cellulose polymers, leading to the emission of gaseous nitric or nitrous acid and acetic acid, respectively. The acidity (pH) of any state of matter (liquid, solid, or gaseous) can be friendly and readily detected using pH indicators. Among these indicators, the most employed is litmus paper, which changes colour following a known chromatic scale in accordance with the pH level. Various tools are used by the community of professionals and insiders in cinematographic archives. In the case of acetic acid emitted by cellulose triacetate films subjected to Vinegar Syndrome, the Acid Detection (AD) Strips® (Image Permanence Institute), Danchek Strips® and Danchek Control Eye® (Dancan Cine Film Service S.L.), and Gastec Detector Tubes® (Gastec Corporation) are the most widely used. Conversely, less known are the efforts to develop similar tools for the early detection of Honey Syndrome affecting cellulose nitrate films. Pros and cons in employing these tools are outlined in this contribution. Although assessing the progress of both syndromes based on the colour change tools is user-friendly and cost-effective, the interpretation of outcomes can be significantly influenced by the user's perception.