you'll need an assistant, plaster and plaster bandages.
have your assistant put on a layer or two of plaster paris and then go over that with plaster bandages for support
you might want to use a moisturizer before hand for easier release
you can also use alginate or silicone;
I prefer using Alja-Safe alginate or Body Double silicone, both from Smooth-On;
you need to decide how many times you intend to use the mold; just once or do you want archival???
Full instruction on this web site: www.bodyscape.net.nz
you can do this job all by yourself keep a basin of water by your side rub vaseline on your breasts wet some plaster bandage and cover your breasts with it do not put plaster of paris on its own on your breasts it will burn you use plaster bandage only if you ar using plaster to make a mould of your skin you can also use algae seaweed rubber what are you planing to cast into your mould