Reno Henna

"The name henna also refers to the dye prepared from the plant and the art of temporary tattooing based on those dyes. Henna has been used since antiquity to dye skin, hair, and fingernails, as well as fabrics including silk, wool, and leather. The name is used in other skin and hair dyes, such as black henna and neutral henna, neither of which are derived from the henna plant...

Whole, unbroken henna leaves will not stain the skin. Henna will not stain skin until the lawsone molecules are made available (released) from the henna leaf. Fresh henna leaves will stain the skin if they are smashed with a mildly acidic liquid. The lawsone will gradually migrate from the henna paste into the outer layer of the skin and bind to the proteins in it, creating a fast stain...

Henna stains are orange soon after application, but darken over the following three days to a reddish brown. Soles and palms have the thickest layer of skin and so take up the most lawsone, and take it to the greatest depth, so that hands and feet will have the darkest and most long-lasting stains. Steaming or warming the henna pattern will darken the stain, either during the time the paste is still on the skin, or after the paste has been removed. Chlorinated water and soaps may spoil the darkening process: alkaline products may hasten the darkening process. After the stain reaches its peak color it will appear to fade, as the stained dead cells exfoliate...."

-http://en.wikipedia.org/wiki/Henna