Resumen
Weld (Reseda luteola) was one of the main sources of yellow dyes used for dyeing textiles and to prepare artists? pigments in Europe until the 19th century. For the first time, this work explores the technology of preparing weld lake pigments in the 19th century by Winsor & Newton (W&N), a renowned supplier of artists? materials. Five recipes were discovered in the W&N 19th century Archive Database and reconstructed in the laboratory. W&N was extracting weld in neutral and basic media, and preparing the insoluble lake by complexation with Al3+ in the form of alum (KAl(SO4)2?12H2O) or hydrated alumina (Al(OH)3). Five yellow lake pigments were successfully obtained and characterized by High-Performance Liquid Chromatography-Diode Array Detector (HPLC-DAD) and Fourier Transform Infrared Spectroscopy (FTIR). Their chromatographic profiles display as main yellows, luteolin 7-O-glucoside (Lut-7-O-glu) or both Lut-7-O-glu plus luteolin 3',7-O-glucoside (Lut-3?,7-O-glu). In two of the processes, the presence of gypsum (CaSO4?2H2O) was unequivocally detected by FTIR, being formed as a by-product. This work offers the first identification of weld lake pigments? characteristic infrared bands. The W&N Database proved again to be a unique source of information on 19th-century artists? materials and their commercial preparation. The knowledge gain is essential to ensure effective conservation and authentication procedures.