Pitfalls of dye identification in historical fabrics

This publication presents challenges in dyes identification in archaeological and historical fabrics. The following key points are discussed. These points were highlighted in the course of the analyses of 180 samples of archaeological and historical fabrics dyed with various dyes analysed in our laboratory using high-performance liquid chromatography coupled with tandem mass spectrometry (HPLC/MS/MS). These key points are: (i) the sample preparation procedure that does not lead to the changes in the composition of the sample and, consequently, to distortions of the analysis results; regardless of whether strong or weak acid was used to hydrolyze, the conjugated compounds were not completely degraded, and it was still possible to identify the source of the dye; (ii) the representativeness of the sample; the percentage of dye in the analysed sample could be a significant factor in the interpretation of the results and it seems to be more important than the sample size; (iii) the possible cause why the materials used for the preservation of fabrics during the conservation works may affect the credibility of the analysis; the additives in fibre treatment or the dyeing process could be identified, and they can interfere when the high-sensitivity instrumental analysis is used; (iv) the problem of the quantification of the residual dye in the archaeological and historical fabrics, especially when working with degraded fabric; furthermore, it is essential to consider that the quantitative determination of the dye in the sample reflects its concentration in the solution; (v) the reliability of the results strongly depends on the fabric degradation; it is recommended that samples be taken, if feasible, from well-preserved sections that have not been subjected to contamination or ultraviolet radiation exposed.