Please note! I am learning to make dolls too, these are just things I've learned along my journey and what I think will be helpful for beginners to know!
I use DAS Paper clay. You can find this at Blick's, Utrecht, or on Amazon/Ebay (And apparently at Staples and Walmart) I haven't really had any experience with
any other paper clays, but they're all pretty much the
same. They're fiberous and made of.. fiber.
You can make a BJD out of other materials other than
paper clay. I know some talented BJD sculptors who
use polymer clay, ceramic, porcelain, chavant, and
epoxie. Here's why I think paper clay is the best option to make BJDs out of and why:
First of all, it's the strongest of all the other materials you can use. It's practically crushed up paper/fiber, so when then clay dries, the fiber is all intertwined, so the dried outcome is very strong!
Polymer clays will very easily crumble and are not strong at all. They won't withstand a doll stringing test. Also, polymer clay burns easily, and is not easily fixed when burned. Epoxie, while it's very strong, it makes it hard to edit and revise pieces, also epoxie is very expensive.
Paper clay is cheap, strong, and easy to carve and sand, while remaining durable.
PAPER CLAY- If you've never used paper clay before, you miiiight hate it at first, and here's why, and good things to know before you decide you hate it, lol
It's extremely frustrating to sculpt paper clay because it's so fiberous and quick drying. Paper clay is difficult to sculpt details in when wet. Make your base shapes with it, don't worry about it looking good, smooth or at all like what you want your final product to look. Don't even attempt to sculpt the paper clay. You want to make yourself a handle, a base, so it's something you can actually hold, and sculpt onto. You don't want to try to sculpt the paper clay wet because you might crush it and warp it, while trying to sculpt or add to it. Always sculpt/carve/sand at the paper clay when it is dry, and add new clay on after the base is dry. You can heat your oven to 270/280 F and put your wet pieces in fr a few minutes for quicker drying! If your pieces are small, then the pieces will dry fast and you can continue to sculpt on it, but the larger the pieces, the more likely the outside will appear dry, but the inside will still be wet, so be careful when applying pressure. The great thing about paper clay (at least in my experience) is that it doesn't burn in the oven. I've had small pieces in there for almost an hour and my pieces don't turn brown or brittle or anything (but they are hot, be careful) The whole process of using paper clay is basically getting a base, adding more clay to clarify shape, carving/sanding, and adding more clay, etc.
Don't worry if your base pieces look like turds.
(That's a torso. Just foil with clay slapped on it)
Armatures - Do not get caught up on them! Often times I see people meticulously carving and making their Styrofoam armatures/bases super perfect. It's not necessary and personally a waste of time.They are important, but ultimately they are getting scrapped when you remove them from the paper clay, so no need for anything elaborate. I just use tin foil. I don't cover my tin foil in plastic wrap because all the layers of stuff make it hard to sculpt on. Remember that once you take the tin foil out, you can always fix the insides. The insides will never be perfect, but that's the wonderful part about the insides, they don't have to be perfect because no one will see it! Just remember that it's just a means to get basic shape and ensure your piece is hollow for stringing. I would recommend drawing out what you want your doll to look form the front and side, to scale so you can compare your creation to your drawing for size and proportion reference.
JOINT Engineering - Worry about joints last. If you fret about engineering, and let it affect your sculpting, you're going to have a hard time. Sculpt all the big pieces first; head, torso, legs, arms. Once the pieces are exactly how you want them, cut them and figure out the joints. I'm a super impatient person, so I want to cut the joints out before the limbs are perfectly symmetrical or even finished - This will cause you lots of pain and will elongate the process, so just get everything perfect because you cut everything up!
PRIMING Prime only when you pieces are finished and you are ready to buff your pieces for molding.
Hope this was helpful to some of you, and I wish you all the best of luck in your doll making endeavors!