Colour fading in textiles: A model study on the decomposition of natural dyes

This paper describes an analytical procedure based on GC-MS to identify in textiles the most common flavonoid yellow dyes used in Europe since ancient times, extracted from weld, young fustic, dyer's broom, sawwort and the berries of some species of Rhamnus. Later on, old fustic and quercitron bark were introduced as sources of yellow colours. The method is based on the solvent extraction of flavonoids from raw plant materials (weld, dyer's broom and old fustic), aged and not aged alum-mordanted wool dyed specimens; subsequently, flavonoids are derivatised with N,O-bis(trimethylsilyl)trifluoroacetamide and analysed by GC-MS. The method easily allows the identification of a dyestuff by the detection of the molecular markers apigenin, luteolin, genistein, morin, maclurin, together with 4-hydroxybenzoic acid, 3,4-dihydroxybenzoic acid, 2,4-dihydroxybenzoic acid, 2,4,6- trihydroxybenzoic acid, which survive in aged textiles. Two photo-oxidative degradation pathways for colour fading, one involving the mordant metallic ion and the other the light as a catalyst, are suggested.