The indigo detective investigates colour bleed

Reading Time: 10 minutes

I have a high level of natural curiosity, and when I wonder about something I want to find out more about it. It usually isn’t quantum physics or anything that would save the planet, though maybe every small thing helps? Heck, who am I kidding, I just notice small anomalies and have to scratch the itch.

What was it that made me ponder this time? Nothing more serious than people recommending jeans be soaked or washed with various additions to help retain the indigo dye. Some said to use vinegar, some said salt, some said to use both, and after a bit of research I found that there was a convincing case to be made for all the former being quite deluded. While I tend to come down firmly in the camp of rationality, I thought I’d run some experiments to see for myself.

Super-indigo scarf as arrived from Thailand.

Super-indigo scarf as arrived from Thailand.

These experiments would of course have been very much more difficult if I hadn’t had the perfect articles to experiment with: my own natural indigo dyed shirts and scarves. Why are they more perfect for this than anything else? For starters I know that the dye on these is guaranteed indigo based on the fermented indigofera plant and not a synthetic indigo-blue dye. This is important, and I’ll get back to this. Second, I have a small supply of scarves and shirts, so I didn’t need to go looking for articles to experiment upon.

I’ll describe this experiment as pseudo-scientific at best, for the following reasons:

  • I am using a limited number of trials (i.e. I’m only testing one of each variant).
  • I am not measuring the results in any reproducible way, other than taking some photos.
  • The items I’m testing on are hand-made and not lab-grade identical specimens.
  • And finally, you really have to trust my impressions of this, as if I did have an agenda I could easily manipulate the results to show exactly what I wanted to portray as the truth.

Then again, most of what I’ve read appears to be hearsay and totally unscientific, as in “I’ve always washed my clothes in vinegar and the colours always stay much more radiant than if I hadn’t used vinegar, which I have never tried, but I’m really sure that without vinegar the colours would have leeched right out!”. Which is more along the lines of religious belief than verifiable truth.

Vinegar, salt, spoon and tub

Vinegar, salt, spoon and tub

So what I did was take two of my super-indigo scarves and one of my indigo deadstock cotton shirts, a pack of salt, a bottle of vinegar, some mild wool detergent, a bowl, some lukewarm water, a glass, and set to work. More about the scarves and shirt further down.

Hand-agitating for that artisanal goodness

Hand-agitating for that artisanal goodness

First out I mixed up half a cup of vinegar and a couple of spoons of salt in a bowl of water. I submerged the shirt and first scarf in this and let it sit for an hour or so, giving it a bit of a squish now and again to ensure things were being mixed up nice and proper. After this I removed a glass full of water to check on the colour, and then put the shirt and scarf in the washing machine for a gentle 30 degree “hand-wash”, with the gentle detergent, some vinegar and salt. Oh, and I put an old white t-shirt in with it, just to see if there was any detectable colour bleed.

Then I did almost the same, without the salt and vinegar. I gave a scarf a really good soak, and then washed it, detergent only, hand-wash setting. Again, with a t-shirt.

Hang on there... The water is turning greeny-yellow?

Hang on there… The water is turning greeny-yellow? (White paper under hand)

What was I hoping to achieve by this? For starters, I wanted to know whether the vinegar and salt would make any noticeable difference. Would the colour be retained? Secondly I wanted to see how much difference a go in the washing machine would make. Third, I wanted to see if washing deeply indigo-dyed items with their polar opposite, a crisp white tee, would cause the tee to turn blue.

And what were the results of this trial? Well, soaking did remove indigo dye, no doubt about that. The yellow you see in the photos is actual indigo. “How can this be”, you cry, “it’s not blue!” Well, that is because the indigo dye only turns blue when it oxidises, i.e. dries in air. In it’s unoxidised state it is a greeny-yellow, and that is what is happening when it soaks. The dry dye is diluted in water and returns to it’s original colour, as you would see it in the vats full of fermented indigo plant.

Shirt and scarf before being subjected to vinegar, salt and wash.

Shirt and scarf before being subjected to vinegar, salt and wash.

However, this is not a big problem at all, due to Shocking Fact #2! The indigo dye does not penetrate into the cotton, so the blue you see is actually dye deposited on the outside of the fibres. Think of it as paint, a kind of paint that becomes a bit dusty when it dries. There is only so much of this you can make stick on the cotton fibres before you realise that there is no gain in this. A natural level of application to cotton that is to be woven gives a mid-level indigo blue. The scarves I used for the test have been taken two steps further. First the scarves were woven with dyed yarn, then the finished scarf was garment dyed, i.e. dipped in the dye vats another dozen or two times.

Deadstock mil-spec cotton shirt after enduring soak and wash. Looks better than before!

Deadstock mil-spec cotton shirt after enduring soak and wash. Looks better than before!

Then, oxidised (or as we know it now, dried) indigo paste was applied to the scarf to dry and deposit even more dye onto the fibres. To be honest, I’m not really sure how much added value there is in the final stage, it seems more like a desperate move to me.

From left to right: Original indigo and washed super-indigo scarves.

From left to right: Original indigo and washed super-indigo scarves.

So of course, once submerged in water there was plenty of dye to dissolve. The big question is though, did the addition of vinegar and salt make any difference to the amount of dissolved? None at all. Did a wash in the washing machine make any difference? It certainly didn’t have any negative consequence. In fact, the fabric feels nicer and the colour is more radiant after removing some of the excess dye.

And did the white tees pick up any colour bleed? Not at all, still shiny white.

Scarf before and after wash. In reality almost no difference at all.

Scarf before and after wash. In reality almost no difference at all.

And therein lies a small lesson. According to my reading, very little of what is sold as “indigo-dyed” today is actually the fermented plant dye it is promised to be. Why? Because fermenting plants is time-consuming, hard work and expensive. And also involves aged urine and sundry biological by products, if doing it really traditionally. Mixing up a batch of chemicals to produce a synthetic blue dye is much cheaper and vast quantities can be made up. So how do you know if your new “natural indigo dyed” garment really is what it claims? Give it a soak. If the water turns into something that looks like a urine-sample, it’s the real deal. If it turns blue, you’ve been conned.

Shirt before and after. It's as if the colours have really come to life after a wash.

Shirt before and after. It’s as if the colours have really come to life after a wash.

And the crocking (blue colour transferring to other items) and fading (the change from blue to natural colour cotton) you experience with your indigo garments, in reality that is just particles of dye falling off the cotton fibres. A lesson I learnt from my Grandfather was that if you wanted to keep something pristine, don’t use it. And vice versa. In my case this was a new skateboard, but the principle is the same.

At the end of the day though, what does this mean to you? Well, you can save your vinegar and salt for your fish and chips, and also, don’t worry all that much about giving your jeans a go in the washing machine.

If you’re curious about the scarves and shirts, the full story is here, and the ones I have left can be purchased here.

And those glasses full of dissolved indigo dye? They looked like this:

indigo water

Left hand side: Dissolved dye from one scarf, one shirt, and a mix of vinegar and salt. Right hand side: Dissolved dye from one scarf.






  • Deborah 31/10/2016 at 20:32

    Interesting! Thanks!

  • Moonie 11/09/2017 at 17:37

    Sorry to say, but you’re actually wrong about the indigo colour showing in the water, and if it’s yellow, it’s indigo, if it’s blue, “you’ve been conned.” Quite the contrary for Ajrakh dye, the real source of indigo dye…it will be blue, every time, and I encourage you to read this article to understand what real indigo is. I live in India, have done for nearly 20 yrs, and am careful to buy only natural Ajrakh fabrics, which leave a blue tint on the skin if worn without dye-setting first.

    • nick 11/09/2017 at 17:54

      Natural indigo in water gives a sulphur yellow colour. Once dry it is oxidised and will tint your skin blue. I could find nothing in the article you link to that contradicts this, or indicates that the indigo dye used for Ajrakh prints is any different to the indigofera plant. I have tried several variants, including Thai indigofera and confirmed my findings. Given that there are around 750 variants of indigofera there might of course be deviations.


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