2.4. Dyeing method
A laboratory model glycerin-bath high-temperature beaker dyeing machine was used. A paste of finely powdered dye (25 mg) was prepared with the dispersing agent EDTA (1 ml, 10% w/v), in a ball mill for 10 min. To this paste, water (15 ml) was added under stirring and the pH was adjusted to 8.5–9.0, using Na2CO3 (1 ml, 10% w/v). This dye suspension (100 ml) was added to a beaker provided with a lid and a screw cap. Before closing the lid and tightening the metal cap over the beaker, a wetted piece of cotton fiber was rolled into the beaker. The beaker was then placed vertically on the rotatory carrier inside the tank. The rotatory carrier was then allowed to rotate in the glycerin-bath, the temperature of which was raised to 80 °C (for cotton fiber) at the rate of 2 °C/min. The dyeing was continued for 1 h under pressure. After cooling for 1 h, the beaker was removed from the bath and washed with water. The pattern was thoroughly washed with hot water at 50 °C, and then with cold water, and finally dried at room temperature.