Evaluating Marseille Soap for Conservation Use: A Comparative Study on Linen Textiles

Abstract

This thesis explores the use of Marseille soap, a traditional, plant-based true soap, as a potential alternative to synthetic surfactants in the conservation of linen textiles. While alkaline washing solutions are generally considered safe for sound cellulosic fibers, anecdotal evidence among conservators suggests that Marseille soap may have additional effects, such as mild bleaching or residue retention. Despite its historical use and ecological appeal, its suitability for conservation purposes has not been extensively studied. Through a combination of literature review and experimental analysis, this study evaluates the chemical and physical impact of Marseille soap on linen fabric. New linen was washed using various solutions (Marseille soap, Orvus WA Paste, and water alone), prepared with different water types (tap and deionized) and at various temperatures. The samples were then subjected to artificial aging and assessed using pH measurements, Fourier-transform infrared spectroscopy, color measurement and visual observation. The study also examined solubility behavior of Marseille soap, identified its critical micelle concentration, and measured the pH of a typical wash bath. The potential impact of Marseille soap on textile dyes was also examined, given that pH changes can cause dye migration or fading. The findings aim to assess both the benefits and limitations of Marseille soap, particularly in relation to its cleaning effectiveness, residue formation, and influence on textile stability over time. Results show that while Marseille soap may be compatible with sound, undyed cellulosic fabrics under controlled conditions, factors such as water hardness, temperature, and soap concentration significantly influence outcomes. This thesis provides conservators with essential data to make informed, evidence-based decisions when considering Marseille soap for textile conservation. It also highlights areas for further research, particularly regarding its long-term effects on historic, dyed, or fragile textiles.