Looking Back to Move Forward
Indigo is an ancient dye, used by many civilizations – including Mayan, Egyptian, Japanese and Indian cultures. When indigo became a commodity it started its journey via the earliest trade routes finding its way to Greece and Rome around 300 BC. The Greeks named the blue pigment ‘indikon’ meaning ‘from India’ and at that time it was considered a luxury item. Later it attracted the name “Blue Gold” due to the demand as a high-value trading commodity. ‘Indikon’ became ‘indigo’ in English.
Regardless if indigo is extracted from plants or produced synthetically, the principle of dyeing indigo has never changed.
• Dissolving the dye by reduction involving vatting
• Dyeing from the vat
• Oxidising in the air
The main application area for indigo lies in the continuous dyeing of warp yarn for the production of denim fabrics. The indigo pigment is a water-insoluble vat dye, which is converted to its water-soluble, fibre-affinitive leuco form by reduction (vatting). In the pigment form it has no affinity for the cellulosic fibre.
It’s well known that dyeing denim with indigo is a wasteful process when it comes to the use of water, energy and chemicals. The problematic use of potentially hazardous reducing agents that are needed to make indigo soluble in water, so that it can adhere the yarns, is also well-known.
Since indigo has a low affinity for cellulose, depth of shade is only obtained when dyeing and oxidizing are repeated several times. This means the scale of indigo dyeing ranges is extremely large. Today, most indigo dyeing is carried out on continuous dyeing ranges. A typical rope range set-up would be ball warps of 300-400 threads per rope. Machines of this kind can be up to 70 meters long. The rope length can be up to 25,000 meters. The capacity of rope dyeing machine can be as many as 36 ropes totaling 14,400 yarns. Normally, a rope dyeing machine has 3-4 wetting troughs and up to four troughs are required for post-rinsing. In between machines have up to eight dye becks, with each dye immersion followed by 1-2 minutes of skying (oxidation of dye). Heated rollers are used to dry the ropes. Ropes are subsequently wound back onto beams prior to the sizing process.
The challenge throughout the indigo dyeing process is to maintain a constant liquor pH by balancing the concentrations of indigo, caustic and hydrosulphite. Other chemistries being used may include deaerating and wetting agents, dispersing agents, complexing agents, fixing agents and rebeaming aids. As you can imagine all this uses significant amounts of water, chemicals and energy as well as producing major amounts of effluent.
But now the denim industry is at a point to innovate. How can we give a new chapter to indigo? What does the future of innovation mean? How can we incorporate today’s values for less water, chemicals, and energy usage into the products we produce? These are exactly the questions we posed to our partners for Kingpins Flash / Kingpins 24 – join us Feb 23rd and 24th to discover the latest innovations with a lower footprint.