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