I have been approaching the design of a Ball-Jointed Doll in a Rapid Prototyping manner, tracing profiles from my full-sized working drawing, then transferring that tracing to cardboard, cutting out the cardboard profiles, slotting and fastening them together with wax, then filling in with warm microcrystalline wax. It is working out really well, and I'm seeing the various parts of the 60cm doll coming together rapidly.
After reading several BJD tutorials, and reading the threads in some BJD-Making forums, I can see that no matter how well a first-time BJD artist sculpts with whatever sculpting medium they are using, the first doll always has several problems, usually in the joints, and occasionally in the actual sculpt (non-symmetry, poor proportions, poor finish, and so forth). I've come to realize that it is very important to start and complete the first doll without becoming too attached to it, emotionally. The first doll is a necessary learning process where you can see how many parts are required, how much work it takes to make all those parts, how the parts fit together, and how the ball joints work. Since it isn't going to be The Doll, it is important to start the first doll and complete it rapidly, so the second doll can be started, in which you will take into consideration all the things you learned making the first doll.
How should you do the Rapid Prototyping of your first BJD doll? I suggest using a method that is the easiest for you to do. If it is easiest for you to model in Super Sculpey, then bake the parts in your kitchen oven, then do it that way. If you feel you need to make the cores of each part in styrofoam, and cover that with air-dry clay, and remove the styrofoam later, then do it that way.
The important thing is to start and complete the first BJD. I guarantee that you'll learn one thousand times more by actually making a BJD, than by reading online BJD-Making tutorials and books.
The other day I reversed my Rapid Prototyping process somewhat and made a basic upper leg form from odds and ends, then made a 2-piece plaster mold around that, and cast two basic hollow leg forms in wax. These leg forms don't really have any leg shape to them, but they are hollow, with balls at each end. I encourage experimentation. Traditionally, Art has always been made, by experimenting. Don't be afraid of failure. Failure is feedback, and feedback is always helpful. Failure is part of creating something. Everything you see that has been created has been through the process of failure, until success was achieved.
Today I worked on shaping the upper legs. I traced the outlines of the front and side view from my working drawing, transferred the tracings to cardboard, then cut out the inside of the tracings, revealing the left and right upper leg forms. I attached the difference (cardboard cutouts) between the basic leg form, and the upper leg forms to the basic upper leg wax forms, then started filling in the profiles with wax.
This is a photo of the upper leg form profiles, cut out in cardboard, and the upper leg forms being filled-in with wax.
So, after trying both types of Rapid Prototyping, I'm going to say that the first method seems to work better and faster. What is the big difference? Well, I have to make a mold of each part, no matter which way I do it. Making a generic basic form, molding it in plaster, and casting two generic cylindrical upper legs in wax seems like a good idea at first. The down side is that the tiny little pieces of cardboard that make up the differences in the profile shape of the front and side vies of the leg are just too finicky to work with. It is really much faster and easier to work with the full profile shapes, and fill them in with warm wax, than to mess with the hollow basic forms and small pieces of cardboard.
Even though the filled-in parts are solid, I'm still going to have to make a mold of each part in the end, and cast a hollow wax shape in order to fit a doll together. Since both methods require making a mold, and since the first method is faster and easier, I think I'll stick with the first method for making the rest of the BJD.
After I get the upper legs filled-in, I'm going to start on the torso.
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