Monthly Method: Altering a Thrown Porcelain Bowl

Antoinette Badenhorst working at the wheel in her studio.


My work is thrown on the wheel and altered using pressed coils. I throw up to 20 basic forms at a time, then alternate active working and resting of the porcelain over a six week period.

Control of the drying process begins immediately. I throw on plaster bats then place the pieces in sealed plastic containers. The bowls need to be evenly leather hard for trimming.

After they are trimmed but still leather hard, I begin altering the pieces maintaining a fine balance between re-wetting and drying the walls of the bowls. Porcelain becomes instantly wet and pliable when re-wetted at the right stage, but if too wet walls may lose their shape and start to tear. Walls that are too dry will delaminate (The wall will split in two and look like a bubble in the fired work). NOTE: You may have to rest the bowl at many stages of this process if it gets too wet. Put it back in the sealed container and work on another piece until it is evenly moist again.

1 Mark and score lines on the trimmed and still leatherhard bowl where altering will take place.

2 Attach a thicker, triangular slab or coil on the scored line. Place the narrow end at the base then pinch until the attachment stands out like a fin.

3 Add coils on both sides to balance the bowl. Attach both fins, but only work on one side at a time.


I start by marking areas where I want to split and alter the wall with a charcoal pencil, then score these lines lightly (1). Next, I attach a slab or coil over the scored line, with the narrow end at the base. I pinch the attachment until it stands out like a fin from the main body (2). I repeat the process on the other side, but only work on further altering one side at a time (3). After attaching the fins, I dunk the piece in throwing water that has a few drops of vinegar added to deflocculate the mixture. The movement is a fast dunk that allows the porcelain to instantly soak water back into its walls. I only dunk one side at a time, even if I want to alter both sides. When working this way, be sure to dry off any excess water puddles to prevent weak spots.

4 Quickly dunk the pot in a bucket of throwing water deflocculated with a few drops of vinegar to soak water back into the walls. Dunk one side at a time, even if altering both sides. Dry off any excess water puddles to prevent weak spots.

5 Using a sharp cutting tool, slowly cut along the curve right next to the attached coil then score the coil.

6 Carefully pull one side of the wall away. Score the cut wall.

7 Attach the cut end of the wall to the scored edge of the coil then secure the seams, pinch the walls to an even thickness, and smooth the attachment.


Using a sharp cutting tool, I slice through the wall of the pot along the curve next to the attached flange (4). Carefully pull one side of the wall away, score the cut edge of the wall and the end of the flange and attach the two (5). After securing the seams, I pinch them to an even thickness with the rest of the wall (6), and shape both sides until they are blended and the curve is consistent. After altering the sides, I place the piece upside down on a foam chuck, and cut the rim to the desired shape (7). Once the curves are cut, I refine them and smooth all of the surfaces with a damp sponge (8). With the form complete, I am ready to move on to carving the surface, and mark out the design using a charcoal pencil (9). Next, I carve the design using a variety of tools (10). My carving tools range from blunt for softer clay to very sharp edges for bone dry clay. You must still control the humidity of the clay to reduce the risks of cracking. Cracks in soft clay can still be fixed without trouble, but repaired cracks in dry clay will appear as a scar in the translucency of the final object.

8 After these alterations, allow the bowl to rest and moisture content to even out, then cut the rim to the desired shape while supporting the bowl on foam chucks.

9 Smooth all surfaces with a damp sponge.

10 Using a charcoal pencil, mark the surface for carving.

11 Carve the surface, following the drawn lines. Vary the carving tools used depending on the drying stage of the clay. Tools should range from blunt tools for softer clay to very sharp-edged tools for bone dry clay.


An Ocean Wide (Ocean series), 7 in. (18 cm) in height, wheel-thrown and altered bowl with glazed interior and polished exterior.


  • Janet F.

    That’s beautiful work and I’m sure it is much more difficult than it appears. thank you for sharing the method.

  • Daijo K.

    Fascinating. I’ve never considered altering a thrown form, although I’ve seen it done. Seems like your step-by-step instructions helped me to get past my hesitation of doing more work. The finished piece is beautiful. What an inspiration. Thank you.

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