On hands and feet, 2-4 weeks or a little more sometimes. On arms and legs, about 1-3 weeks, and on soft body parts about a week. Really soft and thin skin, like neck and face, usually a few days. I've had henna on the soles of my feet last well over a month. The lazy answer is http://www.hennapage.com/henna/how/index.html The less lazy answer is fresh henna powder, something sour, something sweet, and an essential oil with terpinols. Mix your henna powder with acidic liquid (lemon juice, OJ, tea, etc.) till it's between toothpaste and pudding. Add a little sweet like sugar, honey, fructose, etc. Put a few drops of an essential oil like tea tree, clove bud, lavender, or cajeput. Stir till blended, try to squish the lumps, but they'll usually fall apart later anyways so don't worry too much. Make sure everything you use if safe for your skin and your senses, clove bud is harsh and smells great; lavender's gentle and smells odd. Cover the henna and let sit in a warm place till dye releases, check it often for guacamole like browning on top. It may take 2 hours or 20 hours, more heat and acidity speed things us. Once dye is apparent, adjust consistency, stir lumps out, and stick it in a carrot bag and get to painting! Practice makes perfect, and experimentation will show you what's best for you. You can learn to adjust your mix and how you treat it to make your henna easy to work with, and get the best stain. Sometimes I go all out, sifting the powder and straining the paste for smoothness. Sometimes I just dump cold coffee into the powder and wish for the best. There's no hard and fast rules. I made henna yesterday from old kiwis and Splenda packets. BTW, it's hard to get juice from a kiwi.