Make a Bowl by Solid Casting

There is another technique in casting besides drain casting, it's called solid casting. As general drain casting is pouring the slip into the mold and when have certain thickness the remains poured  into container back. While solid casting there is no remains, the slip is allowed to semi leather hard in the mold. Actually there is still remains to poured back, but very little just for making a foot rim (fig.4). Another characteristic is the drain casting for getting outer shape, meanwhile solid casting for getting outer and inner shape. Therefore the mold of solid casting could have a positive and negative shape.

Technically solid casting is more difficult. The bowl often stick to the mold. Usually before pour the slip, each mold is given talc powder evenly. Also the slip consistency must fluid enough. When the bowl start to separate to the mold, you can hit by hand the edge of mold for several times, until make a gap between bowl and mold.

The  results of solid casting are more constant (shape and thickness), because drying process more even (have two shape molds: positive and negative). But anyway, there is form limitation for the technique. The form must be simple and wider into the top, such as bowl or cone. The form like vases wide then tapers back can't be done by this technique, because it will be stuck when lifted from the mold. 

1. Pour the slip

2. Wait until the certain thickness

3. Pour the slip back

4. Keep the mold in first position

5. Lift the positive mold

6. Keep the bowl in negative mold

7. Wait until the bowl separate

Casting the Bottle

Many things could be causes unsatisfactory casting. Besides the technique problems also the batch of material either the slip or the plaster. The problems usually the clay stick to surface mold, the thickness takes very long time or cracks on body surface.

We have to different the composition of plaster and water each technique making a certain mold, for press molding, jiggering, jelloying or slip casting. The proportion of plaster and water for slip casting usually 110-130:100. If too much plaster to water the mold has low absorption to the slip, while too little the mold has high absorption but not practical. Because the mold will quick saturated, therefore used several times only.

Slip casting just suite for the high firing. May be the low firing could be, but not practical because not effective and efficient for production. As general the simple formula for slip casting: stoneware clay, ball clay and kaolin. For deflocculent agent, add water glass.

Simple formula:

- Stoneware clay: 60%

- Ball clay: 10%

- Kaolin: 30%

- Water glass: 0.4-0.8%

- Water: 40-50% of weight the clay.

To modified the formula above can add feldspar, quartz, talc or whiting (non plastic material). All can quicker the thickness of the piece.

1. Pour the slip

2. Pour the slip back

3. Put the mold 45 degree

4. Wait until separate to the mold

5. Release each part of mold

6. All released

7. Trim the sphere

8. Final result

Make a Large Bowl (Hand Wheel Technique)

2. Press the rim firmly

1. Put a large clay and make a hole

3. Use both hand to lift the clay

4. Wider the edge

5. Getting wider

6. To steady wider press firmly from the inside

8. Final result

7. Use the hand to make steady

The pictures of above to demonstrate the making of large bowl by hand wheel. Many technique for making a large bowl, depends on habit and practical of the maker. For this technique the clay must soft enough and doesn't need much water to make the pot. In Indonesia, the ceramic craftsmen usually use soft cloth to help lifting the clay in throwing, not sponge or bare hands.

The pictures was taken in traditional ceramic center at Jatiwangi, Jawa Barat, Indonesia. From Bandung it takes 2,5 hours by bus. Jatiwangi is well known of roof tile in Indonesia. The quality of strength is especially liked by most people. Recently the prestige of the roof tile loosed by artificial roof, because more practical and cheaper. I think Jatiwangi needs revolution or drastic orientation changes in paradigm. The clay not just for roof tile but they can be more valuable economically as well esthetic of form.