Novel digital methods for the qualitative characterisation of some acid dyes applied to wool and nylon

The identification of dyes on textile fibres by assessment of reflectance curves is difficult owing to the dependence of spectral reflectance on concentration and spectral interference due to the base colour of the substrate itself. A method of analysis is proposed in which concentration effects are reduced or eliminated by the use of log(K/S) spectra, a function that is analogous to log(absorbance) as classically used in solution studies. Differentiation of the log(K/S) spectrum suppresses interferences arising from the broad background absorption of the fibre, so that the resulting profile generated is a property of the dyestuff alone. The wavelengths at which peaks, troughs and zero crossings are observed may be used to characterise the dyestuff itself. The method possesses greater sensitivity than conventional spectral reflectance or K/S curve analysis. Although the proposed method has been found to have limited utility in distinguishing between closely related acid red dyestuffs that possess almost identical light-absorbing properties, it does afford a rapid and convenient method for characterising acid dyestuffs on wool and nylon fibres.