The absorption of lawsone and henna by bleached wool felt

Bleached wool felt was chosen as a substitute for human hair to avoid complications due to natural pig-ment. Pieces were dyed by immersion in lawsone or henna suspension, and their colors assessed using a Lovibond tintometer and a Hunterlab colorimeter. With lawsone, immersion for 30 minutes was sufficient to dye the wool. The hue and intensity of the color developed id not change significantly when the pH was varied between 3 and 5, in contrast to the electronic spectra of lawsone solutions, in which absorbance decreased progressively with decreasing pH. Below pH 6 the color of the wool varied little with pH and was predominantly red, but above pH 6 the intensity decreased and the yellow component became pre-dominant. At pH 4.5 the intensity of the red component increased with dyeing temperature between 15 and 50øC, and became progressively more predominant. The color developed with henna increased with temperature, and also with time, probably because time was required to extract coloring matter from the plant tissue. In contrast to lawsone, henna gave a color which was predominantly yellow and had a greater blue component over the whole pH range. Both factors were attributed to the chlorophyll content. Sub-stantivity was tested by extracting felts with water and measuring the absorbance of the extract after timed intervals. The extraction rate was unaffected by dyeing time, pH, or temperature. Examination of the extracted wool pieces suggested that a slow reaction occurs on the wool, either producing new compounds which are more substantive than lawsone to wool or changing the mode of attachment, and thereby in-creasing the strength of the interaction