This was my first henna and since then my hair is redder but still dark.

I had chemically treated black hair, by accident.
My hair right now is dark brown with red highlights.

My mix was
4 ounces Ancient Sunrise henna
A mildly acidic liquid
Water to make a workable paste

I put the mix in a gallon size zip lock bag overnight on my counter. I then went into the shower and cut the corner of the bag and used it this way. I put a shower cap over it then a towel and let it sit for 4 1/2 hours. It was so very easy to wash out. I loved the natural smell to me it was like Sandlewood. Since these pix I have hennaed my hair three times.

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

Video How-To
Going red with henna: https://vimeo.com/manage/videos/739464950