Heres some advise for what I use for butoh makeup/clay. I actaully buy a white makeup. Its comes in a meduim size template. Its not powder, but you do have to wet the "clay" and apply it w/ a sponge. I find my stuff at any costume store. The product I purchase is made by a company call Ben Nye. its good stuff!

heya, well, the clay stuff (which is actually ground up sea shells) is only sold in Japan unfortunately. it's totally amazing. but another good substitute is Kryolan's Aquacolor. get the big size if you're doing more than one body. one is good for about 6-7 bodies full coverage.

what i was taught to do to create an even cover was to dilute it in some water or take a wet sponge (use a fairly porous one, but not a sink sponge! you laugh, but i've had friends do that...) and just do a quick covering on a medium section of the body and then pat it with a thick white sponge, kinda like a makeup sponge to even it out. they usually come in rectangles of about 3x4 or so. inches. ha ha! i usually do one appendage at a time so that the makeup doesn't dry before patting. the trick is getting the makeup not to streak or pat all off, so practice with consistency, wetness and sponges. you can look at some of my pics on my profile to see the result. most of the butoh ones were taken using that makeup. good luck!