Cochineal reds in Iberia and France: a comparative study of 18th century tin-mordant recipes to dye wool

The Royal Textile Factory of Covilhã, founded in 1764, is the perfect example of the Portuguese Industrial and Cultural Heritage. Despite its historical significance, comprehensive studies on the dyeing techniques employed in the 18th century remain scarce. Given the influence of French technology on Portuguese wool production, this study presents a comparative analysis of French and Spanish dyeing recipes to understand their influence on the practices adopted by the Portuguese wool industry. Focusing on the production of red dyes from cochineal insects, one of the main colours used in Covilhã until the late 19th century, this work presents the reconstruction of selected 18th-century scarlet recipes. Quantitative and qualitative differences between French and Spanish methodologies were analysed, particularly regarding the use of mordants, the quantities of cochineal, and the role of pH and tin liquor in achieving scarlet shades. The results highlight that although both traditions relied heavily on cochineal, significant variations existed in recipe composition and application. This work contributes to a better understanding of historical dyeing techniques and supports future conservation and reproduction efforts for Portuguese textile heritage.