I usually use alginate when I cast my stuff. I have used it to cast some arcilic items, like an old voldemort wand I made. It's nice because it cures in under a minute, and takes detail pretty nicely too, but I know there is much better stuff out there.
Do you meant using plaster to reinforce the alginate, or to make the positive cast of the hand? If you're looking for alternatives for positive casting, there are a world of options, depending on what you want to use the casting for.
I've cast clay in alginate, a really hard urethane called 1630, even bondo... the trick then is to keep it as dry as possible, blotting out as much moisture as possible. But beware, some casting resins do not like any moisture.