My doll is 1:6 scale and made of paper clay. Each of her hands are about an inch long, and the fingers are very fragile. Her toes have the same problem. Her body in general is not very strong. I'm not going to cast her. In his book, Ryo Yoshida wrote about the coating he uses on his dolls. Will that be enough for my doll too, even though she's much smaller than his? Is there a different coating that will be stronger?
Did you use the tip in the book for putting a wire armature underneath the clay? I think that is key to sturdier fingers. As for the coating, what is in the Yoshida Style book will work fine, but it's more geared towards the making of OOAK art dolls more for display, less for having fun with....at least that's my take. Also another tip I found when working with paper clays is to mix Ladoll and Premier clay so you have both qualities of a stronger substance and ease of workability.
I used string to support my fingers and toes, just built them up a little at a time, and even it they snap, they're still attached, which is super useful when carving and readjusting the pose.
I made a little photo-series of the process I used when making the hands of my doll, who is also 1/6. I used polymer clay, which I recommend for small parts as it allows finer detail and remains flexible, not brittle. Follow the link to flickr for a detailed description of each stage. howimakehands [View Full Size!] Hope this might help?!
the coating is gofun (seashell powder) mixed with a binder (white glue or something like it). I wouldn't expect it to provide much structural support...