The introduction of natural dyes into modern textile dyehouses requires the classification of products of standardised quality with regard to
colour depth and shade of the dyeings. Canadian golden rod was chosen as a representative example to test the methods that are available to
assess the quality of different crops of plant material which had been collected over a period of five years. Aqueous solutions containing the
extracted flavonoid dyes were characterised by means of direct photometry, measurement of absorbance after addition of FeCl2, analysis of total
phenolics (TPH) in the extract and dyeings on wool yarn.
TPH calculated as gallic acid varied from 62 g/kg to 97 g/kg of plant material; only one sample exceeded this range with a value for TPH of
142 g/kg. Correlation among TPH, photometry in the presence of FeCl2 and lightness of the dyeings can be used to characterise samples. However,
correlation between the photometric results and colour depth of dyeings is not sufficient to permit characterisation of the plant material with
regard to the final dyeing. At present, a combination of laboratory dyeings and CIELab coordinates was found to be suitable to establish an
experimental basis for standardisation of plant material.
2006 Elsevier Ltd. All rights reserved.