A NOTE ON MILLS
Fabric production is the step in the life cycle of a garment that has the highest impact. According to Life Cycle Assessment experts Ecochain, almost 10% of the impact of the apparel industry occurs by producing the fabric, which is made in fabric mills. These are extremely large factories with gigantic machinery which often runs 24 hours, which is why the sustainability of spinning and weaving is very connected to the type of energy that is used.
what & how
Renewable energy sources are the best option. Hydro and wind power require large scale installation, which must be made available to mills by energy companies or governments. Manufacturers have started installing solar panels on their roofs, that fit very well in the countries that produce most of the world’s denim: India, Egypt, Pakistan, Turkey. You can find a great comparison of different energy sources here.
Fibers are cleaned of any impurities like sticks and leaves, this means separating the cotton lint (the white fluff, a mass of unicellular hairs which grow attached to the cotton seed). The fibers are then spun into yarns, that are woven into fabrics and this is where you can add other fibers such as Tencel, Refibra, or bio stretch.
A lot of cotton can get lost during this stage. Mills with advanced technology have vacuum-like machines that will suck up all the lost cotton during the process because cotton is like gold! It cannot be wasted!
Ring Spun vs. Open End Spinning:
+ Ring-spun yarn is made by twisting the cotton strands to make a very fine, strong, soft rope of cotton fibers. Ring-spun yarn is more durable than open end yarn and generally more expensive.
+ Open-end spinning, on the other hand, is a system of spinning where the yarn is twisted by rotating at the hap or break in the flow (the fibers wrap around the yarn vs spinning one long piece of yarn).
In denim, we have two main types of dyes: indigo and sulfur. However, indigo and sulfur have troubles sticking to the fibers on their own. Indigo requires multiple applications to develop the colour, about 6 - 8 dips on top of exposing it to oxygen and stabilizing it before dipping it again.
Chemicals are one of the main components of our clothes, but have gotten a terrible rep over the years. When chemicals are used properly and safely, they can have some serious benefits.
However, heavy use of chemicals causes massive freshwater and ocean pollution, as well as soil degradation, which poses great threat to global food security and biodiversity.
Indigo can be either natural or man-made, but the molecule is the same, and it has to be solubilized with sodium hydroxide (caustic soda) and reduced with sodium hydrosulfite (hydro), regardless of whether it was sourced from the Indigofera tinctoria plant or from aniline and other chemicals. “Aniline free”, which you might see in sustainability communication from brands, refers to detectable amounts of residual aniline that can be found in the indigo dye paste, however the indigo dye is still made from aniline.
Although there isn’t a difference in the way it is applied, the manufacture of the material is very different. Making synthetic indigo is a complicated chemical process with high health and safety risks, which should be done in extremely careful facilities. The chemicals come from petroleum, and we all know the destructive effects that the extraction of it has on the planet.
Most denim, even the one that is used in your vintage looking lighter pairs, is dyed dark, and then reduced in color, which gives a better final result. This means that chemicals are used at the dyeing stage and then later on again (jump to ‘washing’ here).
The yarn has to be treated with caustic soda and a wetting agent to remove natural oils in the cotton and impurities that cause inconsistencies in the dyeing. Rinsing is crucial for the dye to permeate the yarn.
Then the yarns are dipped into several baths of indigo in a continuous rope dye range. The vat is the indigo bath.
If you wanted to add sulfur to compliment the indigo with a cast of black, you would do so before dipping the yarns in indigo during cleaning or at the end after indigo dyeing for different looks.
After the dye is applied the yarns are washed to remove any residual indigo and dried. Indigo and sulfur dyes are not colourfast, so it can be easily removed in the laundry, but more on that later.
To most denim enthusiasts it is very clear what the difference between a woven and a knit fabric is, and they will also know that denim tends to be a twill woven fabric. But here we are speaking to you, curious person on the internet, and we want you to have a clear understanding of what we are talking about. This is not a private club: we want to include everyone! So, woven VS knit. A knit fabric is made up of a single yarn, looped continuously to produce a braided look. A woven fabric is generally produced on a loom and made on many threads, that will be placed at two specific angles. The two angles will then define your warp and weft directions. Denim is a woven fabric, made of a dyed warp and a bleached or undyed weft. This is why when you turn your jeans around they are a different colour!
To set our yarn up for weaving, we need to coat it to ease the friction that occurs during weaving known as a sizing formula. Then we take our dyed yarns for our warp and our undyed natural yarns for the weft!
INDIGO PRODUCTION & DYEING
Today, only 30% of the World's denim Mills use "pre-reduced " indigo which is the most sustainable dyestuff on the market, which requires little to no water and eliminates the wastewater and sludge that powdered indigo creates. It also shields workers from toxic powder exposure and reduces the amount of waste salt by 70 percent.
There is something in between natural indigo and synthetic indigo that might be solving problems both in the manufacture of the dye and in the dyeing process! That is bio-based synthetic indigo (therefore not coming from the indigofera plant, but made in factories from other natural sources). Here we list Huue (previously called Tinctorium), but we hope that many more of these exciting research outcomes will be commercialised soon.
San Francisco biotech firm Huue believes that the answer to synthetic indigo is Genetically Engineered Bacteria to mirror the way the Japanese indigo plant, Polygonum Tinctorium, makes and holds its color. Tinctorium uses E. coli to produce indican, the chemical precursor to indigo, in large bioreactors. The microbial fermentation process can save 100 tonnes of petroleum and 10 tonnes of toxic chemicals per tonne of product. Pili’s process uses about 5x less water and 10x less energy because microbes work at room temperature!
Foam Dyeing is a new water-free process that eliminates the waste created from the traditional dyeing processes. Foam is obtained from an aqueous solution and then spread on a fabric. Pretty neat if you ask me. The foam is made from a watery solution, which includes a foaming agent and a carrier for the dye stuff. The indigo dye is then transferred to yarns in an oxygen-deprived environment sealed by a nitrogen hood. This is a revolutionary process that has been in development for nearly a decade.
The latest development on the market is called Blue Infinity by Crescent Bahuman, however, this technology isn't actually indigo and as we have just learned, indigo is inherently a problem. Learn more about this revolutionary, resource friendly blue dye here.
Research is being one on new options for dyeing, such as working on the natural colour of the cotton, a lesson from the past, and on printing, a potential disruptive technology that could avoid waste.
Some manufacturing facilities have now developed on-site water recycling facilities, so water from washing denim can be filtered and reused. This process saves millions of litres of water with no change to production output, while saving the environment from toxic waste water!
Look for clean indigo dyes that are aniline, hydrosulphite and salt free.
💡 Hot Tip: When choosing factories, be sure to check out their Effluent Treatment Plant! More advice on this from Salli Deighton here.
For more indigo alternatives, head to ”Dyeing to Know About Sustainable Dyes? Sorry I had To.”.
Vertically integrated facilities will generally blend their pre-consumer and post-industrial waste into their products at this stage too and like we learned in the raw materials stage, we want to continue to increase the amount of recycled fibers in our clothes :) But let's keep them microplastic free.
Laser friendly fabrics are fabrics that are designed to be lasered in the washing process. This means that the fabric does not get damaged by the laser, and that the colour responds perfectly to the laser beam, reducing waste in production, and higher durability.
Look for energy efficient facilities that are creative with their resources such as using natural lighting for your factory or using renewable energy.
+ Look for natural indigo labels, however, less than 1% of indigo produced today is from plant based indigo.
+ Look for brands using efficient dyeing methods and aniline free dyes.
+ Buy brands that are disposing of waste in a humane manner such as turning old sludge into bricks that can be used for homes or using water filtration systems that allow them to recycle the water.
To learn more about the indigo problem, read my #DiligentDenim Blog post, “The Indigo Problem”.
what can you do about it?
traceability & transparency
This is a good place to talk about these two hot topics that consumers often find confusing. Many companies have a limited view of the network of business partners within their supply chain, and do not get the full story behind their products. Most know their immediate suppliers, which are the factories that do the cutting, sewing and washing, but information is lost about the suppliers of their suppliers, therefore all the cotton farmers, mills, accessory suppliers, miners of the metals, oil refineries that produce plastic based materials etc. Basically all that has been explained until here is out of reach for most brands, and without this knowledge, it is extremely difficult for them to improve environmental and social practices.
Clean energy certifications to look for:
+ Higg FEM
+ OEKOTEX ECO PASSPORT
+ STeP by OEKOTEX
+ C2C (requires 100% renewable energy)
Dyeing certifications to look for:
+ ZDHC MRSL
+ Clean By Design
Need Help Finding a Vertically Integrated Supplier? Contact Simply Suzette here.