CERAMICS OF PLASTER

Some years ago I got a simple recipe, how to make a ceramics of plaster. A Japanese ceramist made it recipe and in it he said ceramics of plaster may suite for sculptures. It interested me much and had tried to make a sculpture of ceramcs of plaster. But the recipe was too symple, it wasn´t so easy to make it.
Ceramics of plaster is made of plaster, glaze and filler and baked a little over 1000degree. It may look like a terracotta, a stoneware or a porcelain, depending on how much you use glaze and what you use as filler. But its hardnes is almost as same as terracotta.
You can use the mixed liquid just as same as plaster liquid. It become hard in half an hour. So you can use it in casting method, too. You can cast the mixed liquid even into a silicon mold just like plaster liquid. When you have taken the casted work from a mold, it is ready to bake. Of course you can put glaze on it derectly before baking.

HOW TO MAKE
1) First you take some plaster, glaze and filler in the relation of volume 10: 2-4: 10. And mix them togather without water.

Materials
- Plaster: It can be quite normal for sculpture. I have not examined what plaster is better.
- Glaze: Earthware glaze works well. Its baking point is between 1000-1060degree. Frit may be good as well. But I couldn´t succeed in its use yet. I don´t know about stoneware glaze. If you use it much, the ceramics become harder and look wet. If you use it little, the ceramics become weak and dry looking. Another important thing is its effect to shrinking. If you use it much, the work shrinks much and it may get cracks. You take much risk. I recommend you use it little for first time.
- Filler: Filler can be any thing, which dosen´t chage its body in baking. But I recommend next materials.
White shamotte ( white pouder of ceramics) 0-1mm: If you use it, the work dosen´t shrink much. You can bake it safely. But surface of it is rough.
Pouder of porcelain C grade: This make the body of work earthware-like.
Pouder of quartz 200mes: It make the work porcelain-like.
Generally speaking you get your work safely by using rougher filler. You can also make ceramics of plaster without filler. That time the work shrink much, if you succeed in baking. otherwase it cracks.

2) Take some the mixed pouder aside for future repairing.
3) Take water into a bowl (10-12 in volume relation).
4) Put the mixed pouder into the water and mix well.
5) Cast it into a mould. The very important thing this time is the thicknes of work.

If the model is very small - under 5cm high, probably you can cast the liquid to full. If it is relief- the thicknes in about 3cm, you can cast it to full. Otherwaze you should make its thickness thin - about upto 2-3cm.

6) Take the casted work from the mould, and repair it, if neccessary. You have the mix pouder a little.
7) You can glaze on it, if neccesary.
8) Bake it in a kyln. You should bake it slowly from first to end. If your work is a relief and its saze is about of 30x30cm, the temperature is to raise 100 degree by an hour.
If your glaze melt between 1000-1060 degree, bake it until 1020 degree.

The work is ready!

MERITS
- It dosen´t shrink in a mold, when it become hard. So you can use molds, which is made for plaster casting.
- From the same reason you can also use a rubber mould and rubber-like mould.
- You can change its look easily by changing filler.

DEMERIT
- It shrink a little after baking 4 - 15%.
- The high of shape get down a little like stoneware. If the work is a relief or relief-like, it dosen´t mean much. But if the work is standing statue, it may make much probrem.
- No one know what value it has. Is it expensive or cheap?

MORE INFORMATION

MATERIALS
Plaster(gypsum)
- If you use it more, the work is stronger before baking but it shrink more after baking.
- If less, the work is weaker before baking but it dosen´t shrink much.
Glaze
- If you use it more, the work become harder and more stoneware-like but it shrink more.
- If less, the work becom weaker but shrink less.
Filler
- If more, the work is weak befor baking but shrink less after baking.
- If less. the work is stronger befor bake but shrink more.
Water
- If more, the liquid is easy to cast but the work is weak before baking and it shrink more.
- If less, the liquid is thicker. It is not easy to cast. It shrink less.

HOW TO MAKE THIN
Casting in layers
- You can cast the liquid in layer, if the work is bigger, just as same as plaster casting. But the layers don´t fix each other completely. When you have baked it, you may see the problem.
Casting all at once
- If possible, I cast it at once and I take off some plaster from inside. This time the quality of the body is even.

SOME WORDS AT ENDING
If you try it, you should try from a small work. If it works, you can do a bigger one. One big problem is how to make sculpture empty. Casting in layers may be only the way. But every layer may shrink differently, and it may crack. It wasn´t easy for me to succeed in making thin. Probably you should start from a small relief.

17.11.1997 Goro Shintami