About Mehendi (Henna)
Mehendi is the application of henna as a temporary form of skin decoration in Indian Sub-continent. Mehndi decorations became fashionable in the West in the late 1990s, where they are sometimes called henna tattoos.
Henna is typically applied during special occasions like weddings and festivals etc.
In some Indian festivals every woman tries to have Henna done on her hands and feet. It is usually drawn on the palms and feet, where the color will be darkest because the skin contains higher levels of keratin which binds temporarily to lawsone, the colorant of henna.
Henna was originally used as a form of decoration mainly for brides.
Henna paste is usually applied on the skin using a plastic cone or a paint brush, but sometimes a small metal-tipped jacquard bottle used for silk painting is also employed.
The Mehendi is kept overnight and when first removed, the henna design is pale to dark orange in colour and gradually darkens through oxidation, over the course of 24 to 72 hours. The final colour is reddish brown and can last anywhere from one to three weeks depending on the quality and type of henna paste applied, as well as where it was applied on the body.(thicker skin stains darker and longer than thin skin).
Reference : Wikipedia