Here's my (longwinded) $.02:
* First off, there's no such thing as "black" henna. Henna only comes in one color: red. I tried to look up the ingredients of the Hemani henna brand you mentioned but hit a wall. I would hesitate to purchase anything I couldn't read the full ingredients list for, especially henna. When they have the different pre-mixed "blends" some companies actually add metallic salts for better color processing (but these metals can later wreak havoc in your hair strands if you use a commercial dye or give you a nasty allergic reaction). Most likely, this brand you mentioned has a premix of "indigo" (which some people refer to as "black henna"). So just keep that in mind before using this product, and I'd recommend:
http://www.hennaforhair.com/faq/index.html as a good starting point for you to do your own research. One thing that makes me leery is the 30-40 minute processing time, and other's can chime in but that, for me, is unheard of for any significant or noticeable results using 100% natural dye. You also mentioned it is "safe for drawing on hands" so it COULD be BAQ, but I don't use anything that doesn't specifically state that. After all, who didn't draw on themselves with Sharpies at some point in their life? And I wouldn't exactly call Sharpies Body Art Quality marker.
*Secondly, DO A PATCH TEST. I can't stress enough how much doing a patch test, or tests on shed hair that you save, can really save you from a bad henna experience. Henna is definitely not for everyone, but I think it's possible to realize that with very little hair heartbreak. Doing a patch test will also tell you exactly what you will get with your henna mix before you attempt a full head application.
*CurlyNikki describes her henna experience as "an orange crayon on black construction paper" and I couldn't agree more. That has been my experience, only a "red" or "auburn" crayon. Some people get more "orangey" tones and some get more "reddish." This varies depending on the brand, but also the mix, and your own unique hair chemistry, I think. Some people definitely get more dramatic color results, but my own is just a reddish halo/sheen in natural/very good light. For the most part, my hair is just shinier. I will say that my hairline has always had a honey brown/dark blond color and with the henna it is unmistakably auburn.
* I don't process my henna with "boiling" liquid. From my research, very hot liquid has the potential to destroy certain beneficial properties of the mixture. I think most people who use "boiling" liquid do so for faster processing (they're in a hurry), but for myself (and what I'd guess is a lot of ladies on this thread) time is rarely an issue. I personally like to give my henna plenty of time to dye release, so I'll let my mixtures sit for several hours, overnight, or longer. I get excellent results practically every time. I use warm/very warm liquid, no temperature I couldn't comfortably drink.
*posters ^^^ listed a chart of different ratios of indigo to henna in mixes. So, if your dye is natural, most likely it's indigo giving it that color. Black walnut hull can also give very dark/black tints to your mix. There's loads of recipes for different color variations. Keep in mind that anything that wouldn't stain your skin/counter is not going to be an effective dye for hair. Natural dyes essentially work by staining. Also, the effects of henna tend to be cumulative. I'm coming up on my 2 year anniversary of using it FREQUENTLY and only in the last 6-8 months have gotten "noticeable" color change (and some people think I'm imagining the tint, so that should give you a clue on how subtle the color changes can be).
*Re: curl loosening/manageability: I think it's the weight of the dye particles that lend to this effect for some people. I have noticed more manageable, stronger hair, but no changes in texture or curl pattern. I think most people who have curl pattern issues are S-curls (looser/wavier patterns) but coily girls like myself don't have that issue as often. Then again, only time can really tell.
HTH!
I've never used henna before but I am interested in it for the hair strenthening properties and also possible loosening my curl patturn. I just want more manageable hair... I do not want to die my hair red and I will only use indigo if I have to... I went to my henna USA and saw a brand of henna called Hemani. It is supposedly pure henna with something added to get the black color... Here are the dispcriptions on product page... Method of Application: Pour Henna Powder into a bowl. Add Boiling water gradually then stir slowly until you get a creamy thick liquid. Apply the mixture over Dry Clean Hair and keep it for 30-40 minutes then wash properly....The paste can also ben applied on Dry Clean Hands in desired drawing...
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