I have used the Henna Powder/paste before, but I don't think it works for me. For almost 2 years now, I have been using this product called Henna Wax Color Treatment. It is made in Germany and recently just introduced here in the US. It is used exactly the same way as the Henna Powder/Paste. However, with the Henna Wax Color Treatment, since it is already in the form of a cream, you don't have to go through the hassle of mixing. Henna Wax Color Treatment is ready to use.
Whether you use Henna Paste or the Henna Wax, you need to apply it on your hair and leave it on for at least 4 hours to see significant result. With the Henna Wax, which I have personally used, after application, I use a hair steamer for 30-40 mins and keep it wrapped with a plastic cap. Before I had the hair steamer, I just use a damp small towel, which I warm up in the microwave and wrap it on my hair, then cover with a plastic shower cap. Leave it on for at least an hour. Sometimes, I apply the Henna Wax at night and rinse it the following morning.
When applying the Henna, you have to use gloves and plastic or glass container for the Henna mixture. Try to use dark towels because the Henna does stain. Once application to hair is done, immediately wipe everything (tub, sink, etc) clean so the stain does not become permanent. Wash stained materials immediately too. I have stairned a couple of shirts and towels, but they come off when washed after use.
If you have been using a permanent hair dye prior to using the Henna, it may take 2-3 Henna applications before seeing good result. Based on my own experience with the Henna Wax, it took only 2 Henna Wax applications in a period of 1 month before my hair started looking nicer and healthier. Use of Henna could be affected by a couple of factors which may include prior use of permanent hair dye,natural color and texture of the hair, length of time it is left on the hair, amount of heat left on the hair during the dying process.
The reason I use Henna is because my hair has turned brittle from long use of permanent hair dye and highlight, which I started using to cover my gray hair. My hair was so dry and damaged. I discovered the Henna Wax 2 years ago and have been using it since then. I have had very good results from using the Henna Wax Color Treatment. I hope you find the information I provided helpful.