Friday, July 16, 2010

Plaster Mold Making

Before I get into today's work, I'd like to point you to a very nice series of BJD Making videos over at Youtube. The Gnomie Channel has a delighful series of BJD Making Rants that are worth the time spent to watch. Watch them all, then let Gnomie know how much you liked them. She is showing her BJD Making progress on a Fantasy BJD Centaur.

The other day I made a lower leg using a cardboard cereal box armature. This photo shows the tracings I made, and the cardboard cutouts, with the slots cut out.

Here, the two pieces have been joined together at the slots, and fastened with some wax pellets.

Another view of the cardboard lower leg armature.

An yet another view of the cardboard lower leg armature.

Another view.

Once the cardboard armature is securely fastened together, warm wax is applied with a knife, and shaped to the profiles. This is the second lower leg piece being roughed-out in wax. This works up quickly, and has enough weight and structure to support more pieces.

The other day I made a form of the upper leg using a toilet roll core, a wooden knob, and a plastic knob. Is nothing sacred? My wonderful BJD to be has such humble beginnings. In order for me to use the form I made, I must translate it into two wax leg castings. In this photo, I'm showing how I've prepared the upper leg form to be molded in a two-piece plaster mold. Before I did this, I very carefully drew a pencil line around the long midsection of the form. Then I laid the form on a piece of cereal box cardboard (isn't that stuff handy?) that was about an inch or so larger all the way around, and used a pencil to draw a line around the form, onto the cardboard. Next I cut out inside the line I drew, and fitted the form inside the cardboard, so that the cardboard was on the line I'd drawn around the midsection of the form. The idea was to divide the form in half, longways.

I fastened the form to the back of the cardboard with some warm wax, making sure that the cardboard stayed on the line all the way around. That also filled-in some of the little gaps that were there from my cutout.

Finally I put some wax at the top for a pouring hole. This is important to remember if you are going to pour liquid wax into a damp plaster mold. Next I rubbed a very thin layer of Vaseline over everything on this side of the cardboard. The Vaseline is the separator which allows the form to release from the mold after it is finished.

To mix the plaster, I first put enough water in a clean mixing bowl to cover the form. I just guesstimated this amount by eye. If I didn't make enough, I could mix up a little more and add to the mold. If I made too much, I could just throw the excess out. It is important to remember to never put plaster down the drain. If you do, the plaster will harden in the drain, and it will be stoppped-up. Prepare ahead of time when mixing plaster, and have a bucket of water ready to wash out your mixing bowl and your hands.

I sift the plaster from my 100 pound bag of plaster into a clean dry bowl. Then I add that sifted plaster to the water until a dry lake bed appears. At that point I stop adding plaster, and with my hand, push the plaster down below the surface and gently squish it up. It is now ready to be put over the form. I always cover the form first, patting the plaster gently so it will cover the form without leaving gaps or air bubbles. Once the form is covered, I fill in the rest of the mold.

This is what the first half of the mold looks like. Note that I rested the cardboard divider on a couple of pieces of wood, to keep things more or less level. The plaster was of a very thick consistency, so I could apply it easily, without it running all over the place. I didn't need to use any walls for this simple mold. I just kept adding plaster, and scraping the sides, until the plaster was too thick to apply any more. When it sets, plaster gives off heat, so as soon as I was finished applying plaster, I took my mixing bowl and spatula to the bucket of water and cleaned them, and cleaned my hands in the bucket. Remember, never put plaster down the drain!

After washing my mixing bowl, spatula, and my hands in the bucket of water, the first half of the mold had setup. I turned it over and removed the cardboard and the wax, being very careful not to disturb the form which was half embedded in the first half of the mold.

To do the second half, I used a knife to carve some registration tabs around the edges of the first half of the mold, and I added another piece of wax to the pouring hole, aligning it with the first piece of wax, which was embedded in the first half of the mold. Then I applied a thin layer of Vaseline to this side of the plaster mold and the form, to act as a release agent, so the two halves of the mold would separate later on.

I mixed the same amount of plaster and applied it to this side of the mold, making the second piece of the 2-piece mold. I was able to fill in some holes on the outside of the first side of the mold with leftover plaster, after I'd made the second half.

Here, the two halves of the mold are shown. See the registration holes I carved in the first half, were filled in by the second half. Note that the holes I carved didn't have any undercuts. Undercuts would lock the two halves together. The registration tabs assures that the two halves will fit together and make a clean cast with an aligned seam.

Note that there is a pouring hole at the top of the mold. That was formed by the pieces of wax I attached to the cardboard divider shim in the beginning.

Next I use a knife to trim off any sharp edges around the mold.

Once the mold has been trimmed, I dampen it with water, and sponge out any excess water from the inside of the mold. Wax and water don't mix, so I can pour liquid wax into this damp mold, and the wax cast will not stick to the mold.

I melt the wax in my wax pot, then carefully pour the molten wax into the damp mold. When the walls have thickened up enough, I pour the excess wax back into the wax pot. Now I can run some cold water into the hollow of the casting to help it cool faster. When it is cool enough, I carefully separate the mold halves, and remove the wax casting.

I repeat this casting procedure to make the second casting. Now I have two basic forms for the upper legs.

Here is a photo of the rough pieces of my BJD so far. I have two feet, two lower legs, and two basic upper leg forms. The next step will be to roughly model the upper legs. After that, I'll start the torso.

This is a photo of the c.1989 Jill Doll wax originals. You can see that I used the same technique of making a cardboard armature for the wax. You can see some marbles in the top of the feet. There are also marbles in the knees of the legs. The upper and lower arms were also modeled separately, but there don't seem to be any ball joints in the elbows. The torso is also in two parts, divided at the waistline, above the hips. I'm still trying to figure out what I was thinking when I designed this doll in January 1989. I'm pretty sure I was influenced by Bisque ball-jointed dolls I had seen in Doll Reader magazine, but it looks like I wanted to make a more realistic figure.

Next I'll start working on the torso. After the torso, the arms. Then the hands and head. The joints will be the final pieces to make. This doll is coming right along.

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  1. What an amazingly complex process, K. This is why I changed over to sculpting in wool. I have to say that your sculpting skills are very fine!

  2. Thank you Laura. Your wool sculptures are wonderful. :)


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