The Mehndi Henna Application Process:

The finished paste is placed into a cone. During the process of laying out the design, the cone does not touch the skin, but rather, the henna is laid out onto the skin like a fine thread. The flow of the henna must be controlled in order to produce an even line, and requires skilled hands.

After the henna design is laid out on the skin, a mixture of lemon and sugar is dabbed over the design to set it. The longer the design is left undisturbed, the deeper the color will be. If possible, you should leave it on for at least 5 hours. Later the henna is removed by scrapping it off, revealing a reddish color where the henna touched the skin. The color left behind darkens over the next 12 hours or so.