If you've followed my BJD sculpting masterclass, your prototype supposed to be hollow for the doll to function correctly. To prepare each part for mold making, we need to cover all the holes and deeper crevises with plasticine. If hardening plaster will seep into the hollow parts of the doll, you won't be able to get them out of the plaster. That's why it's important to take this part slowly and seriously.

Fill each hole with plasticine. Try to do that as smoothly as you can.

Since plaster molds are rock hard, all the deeper crevices need to be covered with plasticine as well. Think about it as simplifying your prototype for an easier mold making process. After casting your doll from porcelain or air-dry slip you'll be able to refine these details again.

This part behind the ears is creating undercuts (see the lesson about undercuts for more info), if we wouldn't cover it with plasticine, the ears would be stuck in plaster and we wouldn't be able to open the mold without ruining the prototype.

You can see how I'm working with plasticine in this video:

When covering the joint sockets, leave a little rim uncovered. This margin will allow molding the joint sockets as well. We've worked so hard to make all the joints fit smoothly, losing this detail in the molding process would make harder to achieve functioning cast of the doll.

Don't forget to fill in nostrils or inside of the mouth if your doll's lips are slightly open.

Do the same with all the parts of the doll. Covering each socket but leaving a little rim around the perimeter.

Joints have to be covered as well. You can leave a slight indentation where the cutting lines are, so when you cast a new doll, you'll know where to cut them again.

Torso, legs, arms - all the pieces get the same plasticine treatment, haha.

I also advise to fill in the spaces between the fingers because molding each finger separately can be a tough task. Even if you succeed and make a mold with all the fingers separate, casting them with porcelain later will be really hard.

Continue covering all the pieces with plasticine.