Since Henna for Hair opened and I added my original mix to the section, I've made some changes to how I do things and have a color I am much more pleased with. Now that I've gotten consistent results three times in a row, I'm comfortable sharing how I did it.

To start, I've been hennaing my hair for almost two years, now. My hair is a medium brown shade naturally, and the henna build up, while a gorgeous auburn, was not the true ginger-red I wanted. In May of 2004, I enlisted a friend, and, using an at-home bleaching kit (40 vol peroxide) we added what were intended to be highlights but turned out as most of my hair. The result was amazing--I had gone from a deep auburn to a brilliant true red with a few of the auburn streaks remaining. I decided to keep up the bleaching because of this.

I bleach before I henna because I feel that the henna helps some of the damage that the bleach causes. I use 40 vol peroxide, and section out the top of my hair. I add bleach only to the roots, trying not to overlap the older, hennaed and bleached stuff, let it develop to a medium to dark blonde and then wash it out. I spend the next 18 to 24 hours laughing at how silly I look with blonde roots and red hair. Because my initial "highlighting" took up so much of my hair, I decided that it was easier to just bleach all of my roots than try to find each tiny, wispy bit of highlighted hair and match those. Be careful not to get bleach on your skin, though, it IS caustic and it WILL burn.

My henna mix is still relatively simple. I take about 150 to 200 g of henna (My hair has been cut since my last mix and is now to the bottom of my shoulder blades, and thin). This is then mixed with a mildly acidic mix. I usually use about a cup and a half of liquid for this much henna, but it does vary depending on which henna I'm using. I leave this to sit, covered with a layer of plastic wrap and a paper towel to check for dye release, for about a day. This is slopped onto my head 24 hours or so after I've washed the bleach out and I keep it on for 2-3 hours, wrapped in a few cheap plastic shower caps, saran wrap around the edges, and a warm hat.

The initial results are very, very bright because of the fresh bleaching and the combination of "brand new henna day-glo orange!" This fades in a few days, though, and leaves me with hair that looks completely naturally red.

Notes and references
Henna: https://www.mehandi.com/Mehandi-com-Ancient-Sunrise-Henna-for-Hair-s/121.htm
Don’t have fruit juice on hand? Keep some fruit acid powders in your cupboard.
Mildly acidic liquid: https://www.mehandi.com/Fruit-Acid-for-henna-dye-release-s/299.htm
More info on mildly acidic mixes: https://www.tapdancinglizard.com/henna-and-acidic-mixes/
Ancient Sunrise henna for hair kits with everything included: https://www.mehandi.com/Mehandi-com-Ancient-Sunrise-Henna-for-Hair-Kits-s/124.htm