This research investigates the degradation products and pathway of alizarin in selected conditions of accelerated aerobic degradation. The degradation study is a step toward dye identification on badly faded textiles of archaeological origin. The four major degradation products identified through GC-MS analysis are benzoic acid 4, 2,4-di-tert butyl phenol 5, phthalic anhydride 6, and dimethyl phthalate 7. Benzoic acid and 2,4-di-tert butyl phenol are the major products formed upon thermal degradation, while phthalic anhydride and dimethyl phthalate exist in thermal and peroxide/UV treated specimens. Among the four degradation prototypes of this study, peroxide/uv radiation results in the most accelerated degradation, producing phthalic anhydride 6 as its main degradation product. A degrada tion pathway is also proposed.

Indigotin, indirubin, berberine, palmatine, alizarin, and purpurin are major pigments of indigo plant, Phellodendron bark, and madder. The six pigments were examined using the HPLC-DAD-MS instrument for the purpose of the simultaneous detection of the pigments in a single sample run. The HPLC-DAD-MS method examined the individual pigment solutions in DMSO, a solution containing 6 pigments, and the DMSO extract of the silk dyed with a dye solution of 5 pigments excluding indirubin. The retention times of the HPLC chromatograms, λmax of the uv-vis absorption bands in the DAD analyses, and the molecular ions detected for the compound peaks in the MSD analyses were consistent throughout the analyses of individual pigment solutions, mixed pigment solutions, and dye extracted from silk dyeing. The developed instrumental method of the simultaneous detection of six pigments can identify dye in an exhumed textile if the textile is dyed using any one (or multiple) pigments of indigo, Phellodendron bark, or madder plant.

Berberine, palmatine, alizarin, purpurin, indigotin, and indirubin which were the major coloring compounds of Phellodendron bark, madder, and indigo plant were thermally degraded in 100°C oven in liquid dye form and also in silk dyed with five of these pigments. A mixed dye solution of six coloring compounds was prepared in DMSO solution and was thermally degraded for up to 7 days. Silk were dyed using either a mixed dye solution of five dyes or individual dye solutions and each were degraded for 7 and 14 days, respectively, and the dye was extracted from the samples for the HPLC analysis. The concentration of coloring compounds in the degraded samples were analyzed by HPLC-DAD-MS and the color difference (ΔE) of the degraded silk was examined using a spectro-colorimeter. Alizarin and purpurin were more resistance to degradation than other coloring compounds both when in solution form and in silk dyeings. And such result was verified by the color difference measurement of the degraded silk dyed with individual dye solution. The resistance of alizarin and purpurin to thermal degradation was highly likely due to the fomation of fiber-metal-dye chelated complex by alum or iron mordanting before dyeing.

Methanol extractions of 20 archaeological textiles excavated from burial sites in Korea were examined in comparison to standard natural dyes, freshly dyed silk, and naturally-aged dyed silks for the purpose of identifying archaeological textiles dyed with yellow dye from the Phellodendron bark. Phellodendron bark dye was identified by the presence of both berberine and palmatine using the retention times of HPLC-DAD chromatograms and mass spectral data generated from the electrospray ionization (ESI) source. Extracted ion chromatograms (EIC) were used to quantify the concentration of berberine and palmatine in each sample. The results indicated that three of the 20 archaeological textile samples were dyed with Phellodendron bark based on the significant amount of berberine and palmatine detected in these samples, while twelve samples were determined not to have been dyed with natural dyes from Phellodendron bark. Identification of dye in these textiles would allow for appropriate conservation procedures to avoid further dye loss.

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