Decomposition and Analysis of Carthamin in Safflower - Dyed Textiles

Carthamin from safflower petals has been used for centuries in Asia as a red colorant for dyes and cosmetics. Carthamin is unstable, however, both in hot, aqueous solutions, which causes difficulties in its analysis in textiles, and to light, which results in fading of dyed textiles. We have found, using HPLC and mass spectrometric analysis, that carthamin undergoes a reverse aldol condensation in hot, aqueous solutions. Carthamin can be detected by extracting textile fibers at low temperature using a good solvent, such as pyridine. It is well known that textiles dyed with carthamin fade if exposed to light. This fading appears to occur by photo-oxidation of carbon-carbon double bonds since exposure of both carthamin-dyed textile and of a model compound, 4hydroxy-2,’4’-dihydroxychalcone result in formation of 4-hydroxybenzaldehyde and 4-hydroxy benzoic acid. Assuming that the carthamin is not 100% decomposed by light, the residual carthamin may be detectable after extraction of the textile fibers at low temperature. The demonstration of intact carthamin in museum objects can inform decisions regarding lighting conditions, with the view of reducing photochemical fading.