I use Nupur 9 herbs plus Reshma black henna mixed with lemon juice, water, honey, and a little oil or light conditioner. I leave it on overnight or up to 6 hrs. I love the results. Black hair that was thicker and shinier. Ive used Bigen permanent powder hair color for many yrs 2 wks after a relaxer, which is henna plus ppd for faster deposit and dye release, but havent done henna straight after a relaxer yet. I like Bigen as its faster than henna plus indigo, but I need like 4 boxes for all my hair. It thickens like henna and also loosens curl too.
Im touching up this wknd but will do a black rinse and clear glaze for shine instead of henna this time. I love henna but its so messy. I want to henna monthly, but the mess makes me reconsider. I might just suck it up and do it. My hair was not dry or brittle fromthat mix and it was my first time using henna and indigo (no such thing as black henna...its henna plus indigo). It does loosen curl. Aside from the mess, and how long you have to leave it on, I love it. Im texlaxed. I add Brahmi and other Ayurvedic powders to mine.
ETA- I mixed my henna and indigo to use it, and the dye had released, but I became too tired to apply it. So I froze it (already mixed), and never got around to it for nearly 6 months...when I did use it,it worked just fine.