Why is my henna (mehndi) coming out so light?

-So the other day I used some mehndi my friend got me from India, and it worked really well on my palm (very dark and visible.) However, when I paused for about ten minutes and went back to do my forearm, the design came out considerably lighter, even though I was using the same tube and left it on for the same amount of time! What can I do in the future to avoid this? Thanks in advance.All things being equal, henna will never stain your forearms as darkly as it will your palms. Here's a map showing how henna stains the body. Henna sinks about halfway through your upper layer of skin, never further. So the thicker that layer is, the darker the stain because there's more room for henna. Feet and hands stain very darkly, thin skin like faces and necks stain lightly and fade in a day or three.You didnt leave it on long enough