The henna powder is made by drying and grinding

The henna powder is made by drying and grinding the leaves of a henna plant (lawsonia inermis). Pure, 100% henna always leaves a brown stain: the shade variates according to the quality of henna used, the ingridients of the paste and the methods used when applying, and sometimes the color can darken to almost black, but basically the colour is brown. All products claiming to be "Black Henna" have other ingridients than henna added in them. A chemical dye called Phenylenediamine, referred to as PPD, is often used to create a fast-taking, jetblack result. Unfortunately PPD is very harmful on skin, often causing a so-called chemical burn. This is much like a strong allergic reaction, many people get it and many don't, but I advice you not to take the risk. A black henna burn takes a long time to get better and often leaves a scar.