Markers for Identification of Faded Safflower (Carthamus tinctoriusL.) Colorants by HPLC-PDA-MS - Ancient Fibres, Pigments, Paints and Cosmetics Derived from Antique Recipes

Abstract

Safflower red was prepared by extracting safflower petals (carthamus tinctorius L.) at alkaline pH, after the preliminary removal of water-soluble safflower yellow. Alkaline extracts were used to prepare dyed silk, wool, cotton and paper, to precipitate the pigment, to prepare paint and to produce the antique Chinese cosmetic rouge. All reference samples were analyzed with high-performance liquid chromatography–photodiode array–mass spectrometric detection (HPLC-PDA-MS) after colorant was removed from its substrate by both a harsh and mild acid hydrolysis method. In addition to the red colorant carthamin, four colorless components are markers for safflower. These components were characterized by their retention times, ultraviolet–visible (UV-Vis) spectra and mass spectra and were given the codes Ct1, Ct2, Ct3 and Ct4. Experiments on references clearly indicated that these Ct components, unlike carthamin, withstood harsh acid hydrolysis as well as light-induced accelerated ageing, and that they could be found even in a completely faded wool sample. This made them excellent markers to identify safflower red, even in discolored historical samples or in samples that must be treated in a way that destroys carthamin. These findings may contribute to a better understanding of the manufacturing technology and to better conservation of objects that have already undergone considerable light-induced ageing.

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