My experience is that henna and plain distilled water had the brightest color and my hair curl loosening was more defined.
DarkJoy told me to smooth my hair periodically while the henna was in my hair and that really elongates your curl pattern.
When I first started henna'ing I used a gloss and my liquids were green tea and coconut milk. I mixed in gbp (Sallys) after dye release. It was very smooth but I believe it was basically a conditioning treatment. It didn't cover my few grays well. I am a very thorough rinser. I use an entire bottle of conditioner and plenty of water. However after applying my m/s I would wake up with henna stained pillowcases. I stopped adding the conditioner and the staining stopped.
I recently stopped using green tea and coconut milk as my liquids. A woman from India said just use water and a squeeze of lemon. I didn't change my method then. Darkjoy doesn't use anything except water. She made a comment about other stuff interfering with the henna's sticking/coating ability. That made sense to me. I started using warm distilled water only. My experience was stronger color deposit and more curl definition.
As far as rinse out goes, I think it comes down to what type of henna you use. I use BAQ with a fine sift. I hate twigs and veins in my hair. I think the rinsing takes the same amount of time whether or not it is a gloss or plain henna.
I usually henna weekly. I have been using henna since April. I hope this helps. I use jamila, red raj(horrible sift, great color), henna for African hair and its twin.
