Why does indigo fade?
Why does Indigo fade?
What causes it to fade quickly?
How can I prevent it from fading?
These are questions we get asked a lot, so we’ll do our best to try and answer for you! Natural dyes have a tendency to fade over time, as they are generally less lightfast and washfast than their synthetic counterparts. The rate at which naturally dyed fibres fade can vary from piece to piece, and is caused by a number of different factors. Some colours are more prone to fading — for example, natural yellows are less lightfast and often fade quicker, and reds are also known to be more vulnerable, even in synthetic colours (those who dye their hair may know this struggle!). It usually depends on how often your pieces are used, how often they’re washed and whether they’re exposed to a lot of sun.
Indigo is unique from most natural dyes in that the indigotin pigment actually sits on top of the surface of the fibre, as opposed to being absorbed all the way through. This is also why indigo can run when the fibre is washed, because the excess pigment that is sitting on top of the surface is being washed away. If you’ve ever purchased a pair of blue jeans, and noticed the colour rubbing off on your legs, or noticed that they have faded over time, it is likely that they were dyed with indigo. Even though the pigment is in itself very durable, it is really only sitting on the surface of your fabric.
The actual reason that indigo behaves the way it does comes down to chemistry. The colour indigo comes from the leaves of a plant called indigofera tinctoria. The leaves are green, but contain a blue pigment called indigotin. In order to extract this pigment, the leaves are usually processed by crushing and fermenting. The molecular structure of inidigotin is quite rigid and stable, so it doesn’t want to bond to another molecule (ie, a fibre) easily. Indigo is actually not soluble in water, which means that in order for the pigment to bond to a fibre, it needs to be broken down at its molecular level in the dye vat. This is where the reducing agent comes into action — the reducing agent (which in most cases is sodium hydrosulphite, thiourea dioxide or other natural fermentation processes) strips the oxygen molecules out of the water, and breaks down the indigo molecules so that they can dissolve in water. When the fibre is immersed in the vat, the now green indigo molecules are able to bond and cling to the fibre because of the reduced stage the vat is now in. As the fibre is removed from the vat and exposed to oxygen again, the indigo molecules begin to stabilise again, therefore turning our fibre from murky lime green to the beloved deep indigo blue.
The long and short of it is that there is not much that can be done to prevent long-term colour change from happening, without switching to synthetic dyes. Enjoy the natural colour change, and use it as an opportunity to re-dye your beloved indigo!
If you love dye chemistry and would love to learn more, check out this great article on Reddit (It’s actually amazing! )
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