Thanks for that link. Having seen Japanese martial arts I was vaguely aware of what practitioners wore although I had no idea they were called 'hakama'. In fact, until I saw the link (having not thought about it), I'd assumed they were 'jet-black'—if I may use that term here.

Indigo is notorious for fading—its deemed virtue—but what I'm surprised about is how deep a blue it is here (its deeper than the bluest of unwashed denim). I wonder if any other dark dyes or pigments are added to increase the blackness.

I'm notorious for getting very grubby when stripping machines down for maintenance, etc. so I'm familiar with getting 'black' oil and grease stains out of clothes, it's very difficult and in some cases impossible. The black in oils and grease comes primarily from metal oxides and sometimes graphite, these aren't dyes as such but are in effect pigments.

Some oxides/pigments can be very black (almost neutral) and some of their fine particulates lodge mechanically (and often tenaciously) in the fibers and can stay there permanently (a little like a tattoo in human skin). That said, only a 'small' percentage of a pigment will remain fixed to the fibers but what stays there does so permanently (like carbon black in printer's ink a mechanical mechanism (the binder) is need to hold it there). I'm now curious, perhaps some of these very black materials are a combination of a black substrate pigment buffered with either azo blues and or indigo.

Just a thought.

Indigo is perceived more traditional then black, some places allow indigo, some demand.

By the way, indigo bleeding is not limited to washing, the colour actually rubs off during training.

It is turned around and seen a virtue since your garment becomes uniquely yours as it fades.

Right, somewhere in my past I got the impression that the original reason (before it became fashionable) for why manufacturers started pre-washing jeans was to stop the problem of indigo rubbing off onto furniture, chair seats etc. I recall when I was a kid before the pre-washing era started that the labels on some jeans advised that (a) jeans are to be washed before wearing and (b) they could shrink up to 5% after washing (i.e. buy a sloppy fit).

My mother insisted that jeans be washed first as she warned that I'd be in dead trouble if I got blue patches on her light beige lounge suite. This was a bit of a ritual, blue jeans first had to be washed and then only worn outside until the second wash, brown and black jeans only had to be washed once!

Re indigo fading, even now jeans manufacturers advise not to wash denim until really necessary so as to develop one's own characteristic fade marks. My point about very black materials and pigments was broader than just the hakama, materials such as black felt hats, women's dead-black shawls, and men's monkey suits, black parchment paper, etc. These are as black as the current technology permits—whatever it is.