For an assessment of colour depth the respective amount of plant material used has been calculated for the different dyeings in Table 2, an average amount of 0.65 g of dye precipitate per 20 g extracted plant material has been used for the calculation.
Reference dyeings with direct use of plant extracts and CIELab values form literature both for using iron mordanting are given in Table 2 for comparison.
The equivalent amount of dye precipitate used for test dyeings 1–4 corresponded to 15–17 g plant material per 10 g wool, thus darker dyeings were obtained when compared to literature results where the plant extract was used directly (dyeing 7, 8). Reference dyeings obtained with another Canadian Goldenrod plant material showed very similar results in terms of L*, a*, b* values (dyeing 5,6). The differences between reference dyeings 5,6 and 7,8 also demonstrates the high variability in colour strength between different plant sources. This variability will be overcome by use of a concentrated product which can be standardised more easily [14].
The diffuse reflectance curves of the samples are shown in Fig. 4.