Denim blue is a colour we all know and love, indigo blue to be exact. Without indigo all our jeans would look like our undyed denim (link). But turning denim blue, is not as easy as you might think. So, how does indigo dyeing work? And what are the pro’s and con’s. Let’s dive in!
Let’s get ready
The indigo dyeing process is rather complex, but we’ll take you by the hand. It has 3 major steps: pre-washing, dyeing and post-washing. In the pre-washing stage, the yarns are prepared for dyeing. A bunch of water is combined with several chemicals to rinse the yarns one last time. The chemicals open up the yarns, so the dye can settle in. .
Turn it blue
The yarns are ready for some colour! The yarns go through several – 2 to 9 – dyeing baths, containing a combination of water, indigo pigment and chemicals. With every dye bath the yarns change in color from yellow, to green, to eventually blue. In between baths they’re exposed to air, so that the oxygen can make a reaction with the dye and turn it blue. The more dyebaths are used, the deeper the indigo
The last step in the dyeing process is the post-washing stage. In this step, all the excess indigo pigment and chemicals are washed off the fabric with large amounts of water. The average post-washing process uses about to rinse the yarns. Luckily, with a lot of the factories we are working with, this water is recycled and therefor reused multiple times.
Because of the use of many different chemicals and big amounts of water, the dyeing process is one of the most impactful processes in manufacturing jeans. In the process, chemicals like caustic soda, sodium hydrosulfide and wetting agents are used. Most of these can be filtered out by a good wastewater system, which our factories have all in place. Still, one of the biggest issues of synthetic indigo dyeing is that salts are formed in the process. These salts are not bio-degradable and almost impossible to filter out of the water. Therefor they are released into natural waters, which has a negative impact on the local environment.
The next steps
This is why we are always looking for new developments and innovations inside and outside our current suppliers. We are always trying to find ways to lower the impact of dyeing and we are already succeeding in this. By the great efforts of our suppliers, we’re already lowering water and chemical use and producing less salts. But, as hard as we are trying, there are always ways to do better. The next steps are to eliminate – one by one – all harmful chemicals used during indigo dyeing, and replace them with organic substitutes or new techniques. Further reducing the impact on the environment and open waters. We’re confident that with the effort and time we and our suppliers put in, we will achieve that goal! We’ll clean up this dirty business together!