I actually do Henna as a hobby...currently working on my Certification. (you have to have this in USA to do it as a job).

The North African styles are more triangular and religious looking, as the hindu styles are mosre flowery and loopy.

the many triangles in north african henna represents the bride and the decorations on it are the layers of her gown.

its not a long process, well, not for me at least...but that depends on the artist.
i can usually do a full hand in half an hour and iuse the best quality henna so that it dries fast, and leaves a dark orange stain in about one hour...then over the period of a day it turns dark brown. if you want it to last, smear some vicks vapor rub on it at night...eucalyptus will make it last longer.

getting them done on the palms is just decorative...but im sure in hiduism, there is a more religious meaning...but i havent heard of any yet.
for bridal henna, it is also custom to hide the initials of the groom in the designs on the palm...if he finds it on the wedding night, he will be the stronger spouse...if not, she will be


henna originated in India...as most egyptian herbs and spices did when india was trading back and forth with europe ages ago.
it was used for surrency even.
it was used as adorment for women, as they had no cosmetics back then.

as far as potency goes...make sure your henna is a very healthy green powder....and get it from a good dealer. lots of times, extra pigment is sifted into it so it will sell at the same price of the good stuff.

wet ur fingertip dip it in the henna then smear it on your hand. if ur skin starts to turn orange right away, its good. if not, leave it.