Verifying green claims: A new benchmark for water usage in indigo dyeing

What makes an indigo dyeing process “sustainable?” And what is the average amount of water used to dye denim today? The answer is - we do not know as there has been no benchmark to date that compares processes of denim mills worldwide. There have been, however, water saving claims galore but again, without a benchmark, it is hard to gauge what are genuine efforts at becoming more sustainable and what is greenwashing. Experts estimate that between three to five billion(!) denim garments are manufactured each year, much of it in water-scarce regions.

The Transformers Foundation, the denim supply chain platform and think tank for ethics and sustainable innovation in the jeans industry, believes there should be a universal benchmark by which to measure sustainability in denim production and hence set out to provide one, resulting in the report titled “A reference for water consumption during indigo dyeing. An Indigo Council study”.

“Our task wasn’t easy. Indigo dyeing is a long and complicated process that involves both chemical and physical reactions, and is influenced by the quality and type of raw materials, production methods and environmental factors such as weather, humidity, water quality and more”, says the organisation.

In addition, these factors not only vary from country to country and region to region but also from mill to mill, and even day-to-day within the same mill due to tradition and craftsmanship with recipes, conditions and practices that vary across cultures and regions.

The Transformers Foundation managed to get the top denim mills worldwide together and have them participate in the research whose aim was to define, establish and validate a reference standard for conventional or standard dyeing of denim warps. “Our aim is to equip denim producers with the insights and tools needed to foster a broader, industry-wide shift toward sustainable practices.“

Who participated?

All seven participating mills are recognised global leaders that are known for their high standards of quality and operational efficiency. They were Advance Denim from China, Candiani Denim from Italy, Crescent Denim, Diamond Denim, Naveena Denim and Soorty from Pakistan and Orta Anadolu from Turkey.

Two machinery companies - Karl Mayer from Germany and Morrison Textile Machinery Co. from the United States - provided the technical expertise while certifier Bluesign contributed the independent oversight. In addition to factory visits and desk research, interviews were also conducted to be able to combine data from multiple sources.

“This is a group of companies who compete. For instance, Morrison and Karl Mayer compete for every dye machine in the world, like Coke and Pepsi [rival in their field]. And yet, they sat down together and helped us with creating a standard, or not a standard, but creating information,” explained Transformers’ founder Andrew Olah the magnitude of the collaboration at the webinar introducing the study earlier.

What is rope dyeing, slasher dyeing and indigo dyeing?

Indigo is the dye that gives denim its distinctive blue shade, fading and wear effects. However, it is extremely challenging to use. Indigo - in natural or synthetic form - is a pigment instead of a dye. It is not water soluble and is without affinity for cellulosic fibres.

For rope dyeing, separate ends are collected into bundles to make a rope whereas in slasher dying, one warp set — comprising a sheet of yarns wrapped flat in one layer around the entire width of a cylinder, known as a beam — is dipped into the baths. Unlike a slasher machine, which dyes one set at once, a rope dyeing machine - depending on its design- can dye up to five sets at once.

“The aim of this study is not to champion one process over another. Rope dyeing and slasher dyeing have different uses, advantages and disadvantages, and many mills, including some in our study, utilise both processes in their operations,” clarifies the study at the onset.

The research focused on dyeing only instead of studying total water consumption including pre-dyeing, dyeing and after-dyeing, thus narrowing down on the water used in the washing boxes after indigo dyeing because this is where the largest amount of fresh water is used.

Constants and variables

The study then proceeds to list the constants and variables such as the two methods - rope or slasher dyeing - , using 100 percent cotton warp yarns (not mixed yarns), a similar yarn count, 100 percent pure indigo in liquid form and no additional chemicals on the constant side. Among the variables were the water consumption, the number of warp yarns supplied in a single dyeing session, the speed at which the yarn goes through the machine, the number of indigo boxes or baths that a yarn is dipped into, oxidation length and others.

Taking these constants and variables into account, the study found that the average quantity of water used in the post washers ranges from 13 to 15 litres per kilogram for rope dyeing and 7 to 12 litres per kilogram for slasher dyeing. „A few exceptional cases demonstrated significantly lower usage, with minimum values recorded at 3.85 litres per kilogram for rope dyeing and 3.4 litres per kilogram for slasher dyeing.”

Asked to clarify the opportunities for mills from these findings, Olah said: “The idea of the report was to help buyers see their way through a maze of claims. So if they are interested enough about water, now they have a way to double check claims and of course, Transformers is always willing to assist as well. But in addition, yes, mills who have genuine interest to reduce water usage in dyeing now have an open book on other’s results and can set internal standards. Again, we can help them if they wish. It is all open and freely available to share.”

Takeaways

The most important takeaway is that reducing water consumption in the standard indigo dyeing process for warp yarn is achievable—provided that the challenge is approached with a scientific and data-driven mindset.

Asked by FashionUnited if the study can be used to verify green claims, Transformers’ founder Andrew Olah said: “This report provides a baseline, a way for manufacturers and mills to actually vet their claims with third party data. When it comes to making denim, every manufacturing process negatively impacts our environment... If we make nothing and stay home and grow and eat our own food, probably our impact on the environment is zero but once we have factories to make stuff, we impact. Then the question becomes how badly do we impact and are we doing best possible attempts at low impact?  This is all we can aspire to do. Indigo is messy.  So we can celebrate best production methodology in a dirty process.”

Prior to this study, there was no all-encompassing method for gathering and comparing data on the various chemicals, machines and other factors involved in the indigo dyeing process, preventing the industry from precisely measuring and comparing water usage across dyeing recipes and procedures. “We hope that [the study] serves as an industry benchmark against which claims regarding water consumption for new colouring processes or technologies can be compared,” states the Transformers Foundation.

The study is a must for anyone who wants to know about indigo dyeing, from veterans in the field to newbies who want to just dip their toes in. For the latter, the many illustrations of common processes and procedure will ease understanding while the former can profit from suggested questions that can be used when sourcing denim.

Mills were even asked their thoughts on investing in equipment for the two most common dyeing methods - rope and slasher dyeing. The study ends with an outlook at future studies, which could center around water and indigo recycling, dyeing with less water or even waterless dyeing and creating benchmarks for finishing processes.

The study “A reference for water consumption during indigo dyeing” even comes with a glossary of the most common terminology used in indigo dyeing and can be accessed on the Transformers Foundation website, along with a recording of the introductory webinar.