Take It From Me: Tips On Going From Blonde To Dark Brown Hair With Henna & Indigo
However, I want to make the road way easier for you.
So, please move forward with any henna-over-bleached-hair-and-dark-end-result-ambitions with the following points in mind.
For Quality Results, You Have To Reach For Quality Ingredients
Obviously. But it's really tricky actually. I used to live down the street from an amazing spice shop and their henna/indigo selection was solid. But now I have to order it online and BOY it is a hassle. There is no such thing as "Black Henna"; mixing henna (which can only dye hair red on its own, I believe) with indigo can lead to dark brown or black hair. Read the reviews, sorting them from worst to best to see what the unhappiest customers are saying.
Oh and don't bother with Lush's Henna Hair Dyes. They can provide a nice conditioning treatment and a darker tinge for a few days, but that's about it. I tried "Caca Noir" and the results washed out in less than a month, even though my hair was already a dark color from previous henna-ings at that point.
Oh and you might want to consider buying in bulk...
Don't Take Hair Color "Leaps".
This goes for commercial, off-the-shelf hair dyes too. Look at your mane in the mirror. Is it drastically different than what you are hoping to achieve? Take baby steps! Read up on color theory too; having your hair turn a horrendous green because you didn't add red back in before throwing a dark brown on over a bleached mane is not a treat.
Henna away. But please be warned that your hair is going to be SO bright at first. It's insane. I don't mind standing out, but even I was like, "Let me go grab a beanie..." because I felt like a traffic cone.
Then henna again. And yet again a few weeks later (conditioning all the while). And...more hennaing! Do this until you have built up a base that is burgundy, rather than carrot-red.
Now, you can either henna and then follow this up with a mix of indigo and a tiny bit of henna—my understanding is that there needs to be a bit of activated henna in the mixture for the indigo to darken hair correctly—within 48 hours or you can simply prepare a mixture of henna and indigo. Research ratios first though!
I'd recommend the two-step method since henna apparently should usually be prepared hours and hours before it works properly, while indigo should be applied 10-15 minutes after mixing —you'll know when because it turns blue—so I don't really understand how that math works out...
Know That It Will Require Many Hours Of Work
Going to level with you; applying henna and/or indigo is a total pain. It drips all over. You are plastering a mud-like substance onto your head and you don't want to miss any strands, so it takes ages.
I'd say that you should aim to keep henna and/or indigo on for at least four hours. I know, I know. That is nuts. Some people put it on before going to sleep though, so that's an idea.
It's Not A One-And-Done Deal
Bleached hair is pretty damn porous, so you will likely be dealing with hue fading until it grows out and you can chop it off.
If you're lucky, once your hair is black (or simply dark brown enough for your liking), you will only have to repeat the henna and indigo process every three months for half a year and then you can probably scale back to every six months or so.
Know That Your Hair May Not Be In Peak Condition When All Is Said And Done
Part of this is perhaps tied to starting off with bleached hair, to be fair. But being natural and what-have-you doesn't mean that henna/indigo will automatically restore your hair to its original sheen, shine and texture.
Some people swear it improved their hair. Others, like me, tolerate a bit of extra frizz because I really want a color that matches my roots. I also accept that the formerly-bleached part of my hair is basically beyond repair.
I'm around if you have any comments or questions.