Ever glanced at your pair of jeans and realized that they’ve “grown” since you first wear them? That you’ve got wear patterns where you keep your wallet, phone, keys, or where your knees bend?
Just like the Latin language, denim fades, and all this has to do with age-old battle between indigo and cotton. Grab a seat while we explain why jeans fade.
Most indigo jeans you find in denim today is synthetically formulated in a lab and known as “pure indigo”, but indigo naturally comes from the plant indigofera tinctora aka “natural indigo. Did you know that we’ve been blueing ourselves for nearly five thousand years now? This is because indigo is one of the oldest dyestuffs known to man.
From technical perspective, both are just horrible dyestuffs, but therein lies why we love them so much. Like water and oil, indigo and cotton don’t want to stick to one another.
Indigo molecular composition is quite stiff and stable, that is why it doesn’t naturally stick to a cotton fiber. Indigo has to be broken at the molecular level with other additives to form a dye bath, which then oxidizes back to rigid when exposed to light and oxygen.
Once the indigo adhered, it goes back to its natural state, it become rigid again and creates a brittle lattice on the outside of the fiber.
Most of the time, cotton is dyed when it’s still in a yarn form and before it has been woven into a fabric. Commonly, the yarns running up and down (textile pros call these the warp) are dyed blue in the indigo and the ones running side to side (the weft) are left as it is.
That is why your jeans are blue on the outside and white on the inside.
The warp yarns in classic denim fabrics were dyed by taking the yarns together in long ropes and briefly douse them in indigo, then they emerge before getting dunked again. This process is called “rope-dunking”. This constant exposure and dousing means that they never stay in the indigo long enough for the dye to get all the way to the core of the yarn, so the outside gets blue while the inside stays white.
Since indigo forms a brittle bond on top of the cotton, the two breaks on a molecular level as our jeans crease when from walking and sitting down, from where you keep your wallet and keys, all of it chips away at that outer indigo and exposes the white cotton core.
Nowadays jeans aren’t rope-dyed anymore-they’re stuffed in a big vat where the dye gets closer to the core-they’ll still fade. But rope-dyed raw denim is most likely to give you high contrast fades and the method preferred by many raw denim devotees.
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