Folium in Persian and Islamic Manuscripts (15th–19th Centuries): Historical Significance and Analytical Study

Medieval manuscripts are an essential part of Persian cultural heritage and a rich source of the country’s material culture. Their study sheds light on shared materials across the Mediterranean and Near East. The practice of using blue and purple in manuscripts was popular during the Middle Ages in both Europe and Persia. Persian historical treatises describe a blue dye plant used for paper, in addition to blue indigo, although its specific terminology was previously unknown. The plant is identified as Chrozophora tinctoria (L.) A. Juss., also known as turnsole; the dye extracted from it is commonly known as folium. This study is divided into three phases: First, dye extraction techniques from C. tinctoria fruits were studied based on historical Persian recipes. Second, methods for reconstructing blue-purple paper dyes from turnsole fruits were explored, with local plants harvested in Iran during August and September, and the dyes analysed using spectroscopy, finding a good agreement to folium spectra obtained from European (central Italy) fruits of C. tinctoria. Third, folium was identified on manuscripts produced under Islamic rule in the Middle Ages. The findings suggest discussion as to whether this dye was used in Persian manuscripts too, given the notable corpus of citations in Persian historical treatises.