Non–destructive near–infra–red analysis for the identification of dyes on textiles

A pattern–recognition algorithm combined with near–infra–red reflectance spectroscopy has been modified to function as a non–destructive analysis technique for identifying dyes present on textiles. Samples of 261 dyes and textiles were measured in the 1100–2500 nm region to form a near–infrared (reflectance) spectral library. Principal component analysis (PCA) was used to generate an orthonormal reference library from the library of original spectra. The PCA algorithm treats the spectra in the library as an n component quantitative analysis problem in which each spectrum represents a standard mixture having a concentration of 1. 0 for that component. Spectra of dyed textiles were used as an unknown set in a library search. This new method saves time and materials in comparison with traditional methods of analysing dyes present on textile fibres. The library of dye spectra can be developed from measurements made directly on dye powder without interference from inorganic diluents. The method was successfully used to identify the dyes present on five textiles. The technique is particularly well suited for studying forensic, historic and archaeological textiles because of its non–destructive nature and ability to analyse small amounts of sample.