Walker's mix is 100 grams of Ancient Sunrise henna from Catherine mixed with a mildly acidic liquid. He likes to leave it in at least 4 hours, followed by a thorough rinse, then indigo for another hour.

The last batch of indigo was really good and we're now getting true blue-black, exactly what he wanted! The texture of his hair has been great since starting henna - it had been dry and crunchy, especially his gray, and now it's soft, full and glossy.

This shot was taken about 4 weeks out so he was about ready for another go. His natural color is black with about 30-40% gray, mostly on the sides.

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
Mixing henna and indigo: https://vimeo.com/manage/videos/561559371