Dyeing and denim are inseparable and the widely known and revered phenomenon of 'fading' in jeans is a testament to it. How has the process evolved over time, and why does it exert environmental pressure? What methods can we employ to improve it? We’ll find out in our Durable Dyes. Let's start at the beginning.
How Denim is Dyed
Dyeing denim involves soaking yarn – usually bundled in ropes or spread out as sheets – in a vat with liquids and dyestuff, a powder extracted from plant leaves (natural) or petroleum (synthetic). Most textile dyes require a binder called "mordant" for fixation, but indigo is a pigment. That means it needs a special "reducing agents" to form a soluble dyestuff that can adhere to the textile – cotton in the case of real denim. When the yarn is pulled out of the dyeing vat, an oxidation process fixes the color. This process is repeated several times applying layers of blue, until the color appears saturated. Since the dyestuff only reaches the surface and not the core of the yarn, you get that distinctive fading effect when you wash and wear your jeans.
A Scrap from Peru
The iconic blue jeans look can be achieved in various ways, and the standard has evolved over time. The earliest evidence of fabric dyeing with indigo dates to 4000 BC in Peru. Like all denim produced until the 19th century, it began with the natural extraction of indigo from the leaves of the indigofera tinctoria plant. This 'true'; or 'natural’ indigo was often obtained through fermentation, resulting in a sludge that was later dried into blocks and grinded into powder. Europe found its own version of natural indigo derived from woad, a plant with similar properties, around the 8th century BC. However, true indigo had a better affinity for less absorbent fibers like cotton, making it the preferred choice.
These days, however, almost all indigo is synthetic, produced through chemical engineering. The basic chemical structure of synthetic indigo was discovered in 1878 by the German chemist Adolf von Baeyer, earning him the Nobel Prize in Chemistry in 1905. This synthetic indigo entered the market just before the turn of the century – an immediate success due to its affordability and consistent performance. By 1914, 95% of natural indigo production had vanished, and the woad market had faded into obscurity.
The Invisible Cost of Dyeing Jeans Blue
Dyeing your jeans blue isn't great for the environment. A considerable part of the nowadays indigo manufacturing process is veiled in secrecy, but we know that the coloration of garment production alone is responsible for over half of the industry's greenhouse gas emissions. Indigo dyeing consumes thousands of liters of water, not only for numerous rinses and dye dips, but also for achieving pre-faded looks through washes applied to the jeans. The exact water usage per pair of jeans may be a subject of debate, but the crucial issue is that this precious resource is diverted from other ecosystems that need it more.
Furthermore, the wastewater generated during the dyeing process, laden with chemicals like aniline, cyanide, and excessive salt, poses a significant threat to waterways and the organisms living within them. Workers in the main production hub for synthetic indigo, China, are exposed to health risks including inhaling raw indigo powder from freshly opened sacks or "indigo bombs."
Sustainability: Don't be Fooled By the Natural
The environmental impact may vary depending on whether you use natural indigo or its synthetic sister, but it’s hard to tell which one is worse, says young denim expert Oyunaa Kerssens. “First of all, I', not really a fan of synthetic, why? Many reasons and the main one is because the method of synthetic processing is only accessible to those with the technology and the money, which essentially makes it a non-democratic product. And the negative impact on workers and nature is a consequence of this.” Not to forget that, besides the occasional bio-based manmade indigo in the commercial market, most synthetics are petroleum-derived.
On the other hand, Kerssens acknowledges that scaling up natural indigo production is also problematic due to the substantial land, water, and energy requirements of Indigofera cultivation. It would take up to ten million acres to meet the demand of 70 thousand metric tons of indigo for denim products. Preparing and fermenting natural indigo is labor-intensive, and its appearance lacks consistency. Impurities and crop variations lower the yield of natural indigo, and its lower build-up properties and fixation rates necessitate the use of more dye and water to wash off unfixed dye in the rinsing step, all of which increase
resource consumption and costs.
Kerssens' verdict emphasizes the importance of considering circumstances. “It depends on the context of the product, whether natural or synthetic suits best, such as the distances from producer to factory or the scale at which you want to produce and which customer you want to reach. Ideally, I would choose natural indigo, on a much smaller scale with products
that last a lifetime and with a decentralized production chain close to everyone's home. But we're not there yet”.
Better Dyes Are Coming
Nevertheless, the natural production of indigo blue is the only one that gives the distinctive green hue that customers are willing to pay a premium for. The inconsistency in this sense is a value-adding characteristic. That's why denim enthusiasts are closely following the latest innovations to produce true denim ethically. Similarly, sustainable synthetic dye innovations are on the way, along with methods to achieve the raw look of the original. We'll cover all of these developments in Durable Dyes.
Planet Proper Blog
Keep up to date with news and innovations in the world of denim and sustainable fashion.