Carthamus tinctorius L.: A photophysical study of the main coloured species for artwork diagnostic purposes

Abstract

In this work a spectrophotometric and fluorimetric study of yellow and red extracts from Carthamus tinctorius L. in solution and on dyed textiles is reported. The red dye, precipitated as an insoluble organic pigment, was also characterized as powder substrate and on painting mock-ups using different pictorial techniques based on the use of diverse binders. The dyestuffs were directly extracted from dried petals of Carthamus flowers following ancient recipes adapted for laboratory use. The main quinochalcone dyes (hydroxysafflor yellow A, safflor yellow A, anhydrosafflor yellow B and carthamin) were separated and isolated through both analytical and preparative High Performance Liquid Chromatography–Photo Diode Array and subsequently identified through Liquid Chromatography–Mass Spectrometry Quadrupole Time-Of-Flight analysis. The compounds were then studied in solution so as to supply information concerning the scarcely studied fluorescence of these materials. Based on the photophysical behaviour determined in solution, spectral properties of dyed textiles and pictorial mock-ups were discussed. The results obtained on red reference samples are of peculiar relevance for the non-invasive identification of carthamin whose specific absorption and emission features have been clearly detected on a 16th century tapestry fragment.