Indigo Dyeing Process Section

Endenim analyzer (Endenim has been manufactured as a little series production)

- Endenim product note
- Endenim application note

Field operation results:

- Endenim report recorded in 2003 for light indigo shade
This report shows 10 ppm precision at low indigo concentration


- Endenim reports recorded during years 2004-2005-2006, mainly dark indigo shades
These reports show operation of the analyzer at high indigo concentration, maintenance tasks are described


- Endenim report recorded in 2007, hydrosulfite analysis
This report shows operation of Endenim as hydrosulfite analyzer


- Endenim report recorded in 2008, hydrosulfite analysis
This report shows operation of Endenim as hydrosulfite analyzer. From the reports you can see that preliminary tests in factory show that IHPA technology is promising.

IHPA analyzer(IHPA is in alpha development state). We are looking for sponsors interested in funding IHPA development,
in order to make transition from alpha to production state

- IHPA (IndigoHydrosulfiteProcessAnalyzer) product note

Analyzers architectures

- Analyzers architectures


Indigo Dyeing Process description

Indigo has been used to dye fabric with "indigo blue" since before recorded history. The sap which oozes from the plant when bruised was applied to fabric by ancient Egyptians, Greeks and Romans. Indigo has been used in India to dye fabric for at least 4,000 years by methods which are practically identical to the methods employed today. Indigo was introduced in Europe in large quantities by the Dutch East India Company in the early 17th century.

Indigotin (C₁₆ H₁₀ N₂ O₂) is the true coloring matter of indigo. When pure, indigotin forms a dark, rich blue powder or bronzy blue-colored needle crystals. The most important reaction of indigotin is its reaction with reducing agents. When subjected to a reducing agent, i.e. sodium hydrosulfite (Na₂ S₂ O₄), in the presence of alkali, indigotin combines with two atoms of hydrogen and is reduced to a colorless body, known as indigo-white or the leuco form, which is insoluble in water, but dissolves in alkali, with a yellow color. It is reoxidized to indigotin with great ease, simply by exposure to oxygen.

The commercial vat method thus utilizes these reactions to dye fabric or yarn indigo blue. Commercial indigo vat dyeing is carried out in an aqueous alkali vat containing the reduced leuco form of indigo. Fibers in the form of warp yarns are dipped into the vat for a residence time sufficient to permit the fibers to absorb the desired amount of leuco dye. Following each dip, the fibers are squeezed between rolls and then carried into the open air, which is known as "skying," wherein the leuco dye is oxidized to the insoluble indigotin form in the fibers.

Oxidation of the reduced leuco form in the dip vat is troublesome in all vat dyeing, but is a particular problem with indigo dyeing. The oxidation occurs where the dye liquor contacts the air, especially in the region of the squeeze rolls where multiple interfaces are generated, exposing large areas of leuco dye liquor to the air as the dye liquor drains from the squeeze rollers. This oxidation results in a significant loss of dye liquor and formation of floating scum of oxidized insoluble dye.