On the Use of Fibre­Optic Reflectance Spectroscopy (FORS) in the Ultraviolet and Visible Range (UV-Vis) for the Analysis of Organic Lake-Pigments in a Mid-16th Century Illuminated Antiphonary – a Chemometric Approach

The dye source of the organic pink-lake pigments used to produce reddish-to-pink paints present in six representative illuminated capital letters of a mid-16th century illuminated Antiphonary housed in the Biblioteca Pública de Évora, Portugal - the Manizola 116c - was studied in-situ by non-invasive Fibre Optic Reflectance Spectroscopy (FORS) in the UV-VIS range. Historically accurate reproductions of pink lake pigments were used for calibrating the Principal Component Analysis (PCA) where historical FORS spectra were projected. The chemometric approach indicated the use of cochineal to produce the reddish (cochineal acidic form) and pink-purple (cochineal basic form) hues to obtain the painting layer. Two representative micro-samples were analysed by LC/DAD/MS, confirming the use by the illuminator of cochineal in its acid-basic equilibrium to produce different shades of reddish-to-pink colours across the manuscript