INDIGO DYE RANGE SCHEMATIC
The process in continuous indigo dyeing consists of passing yarn through a series of indigo dyeboxes, which involves padding and oxidation of indigo by atmospheric air.

Box 1: wet out and scour to clean mineral impurities of the cotton fiber

The scouring box and scouring feed consist of VIRCOWET QS-683, VIRCOQUEST 100 and a small quantity of alkali.

Boxes 2 and 3: a hot rinse and an ambient water rinse or sulfur black

Boxes 4 to 9: Indigo dyeing

The initial indigo dyebath comprises of Indigo, VIRCOTONE QS-424, Sodium hydrosulfite and caustic soda. The pH is maintained as close to 11.0 as possible. To replenish the indigo and chemicals used by the continuous passage of yarn through the dye bath, a dye feed and a chemical feed are used. Dye feed mix consists of Indigo, Sodium Hydroxide, VIRCOTONE QS-424 and sodium hydrosulfite. A chemical feed comprises of VIRCOTONE QS-424, sodium hydroxide and sodium hydrosulfite. Typically, in the dye feed just enough chemicals are used to keep indigo in a reduced state, therefore, excess chemicals needed in the dyebath are supplied from the chemical feed. Each dip is about 14-20 seconds depending on speed of the machine and each oxidation step after indigo dip is pproximately 60-90 seconds.

Boxes 10 and 11: rinse to wash off the unfixed dye or sulfur black

Box 12: Finish application

In a sheet range, yarn is passed over drying cans, followed by finish and size application. For a rope range, the yarn cables are sent to rebeaming, followed by slashing.