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Ceramic Art Lesson Plan: Translucent Porcelain
Posted By Antoinette Badenhorst On September 20, 2010 @ 12:19 pm In College Level Ceramics Assignments,Education,Lesson Plans 9-12 | 1 Comment
Before throwing porcelain, it’s important to adequately plan and design what you’ll be making. Porcelain contains more silica and feldspar (the glass-making components in clay bodies) and less clay (the plasticizers in clay bodies), so the body is very open and porous. This means that it is more difficult to work with than other clays since it becomes saturated with water so quickly and collapses much faster.
For best results, wedge porcelain twice: once a little earlier—even a day—then right before use. Once you have centered the clay, coning is also important. Use removable bats to throw on.
When opening the clay, pay attention to the original planning of the bowl. Most of the bowls I create are curved in the bottom so I start with curving the inside. The first two pulls of the clay are quick and intended to create height for the basic shape (figure 1).
Use just enough water or slurry to keep a wall of clay moving above your fingers (figure 2). The slightest dryness can distort the bowl and you might have to start over, so use a sponge to control the release of moisture. Since porcelain is very thirsty and readily absorbs water, it quickly becomes too soft to work and control. Frequently clean water from the inside and make sure the original contour of the bottom is still in place (figure 3).
Thin, shape and compact the walls with the tip of your wet fingers (figure 4). Then, with the wheel at a medium speed, use as much time as needed to create the desired shape on the inside of the bowl. If the inside shape is successful, you can easily trim the outside to follow the inside since it is easier to trim unwanted clay away from the outside.
Use two plastic kidneys, one on the inside and one outside, to squeegee excess slip off and eliminate throwing rings without distorting the form (figure 5). Leave extra clay on the bottom of the sides to provide extra support until the form sets up (figure 6).
About 30 minutes after you’ve finished throwing, cover the piece and protect it from uneven drafts. With porcelain, you don’t want the rims to dry out too fast. You also want to avoid uneven drying, which causes cracking and warping in many porcelain pieces rather than the speed at which it is drying.
By the time the clay releases itself from the plaster bat, it’s dry enough to trim the foot rim. Very carefully place the bowl with the rim down and centered on a foam-covered bat (figure 11). The bat has holes that fit onto the pins on the wheel head and the foam is marked with rings to help me find the center with the least handling of the pot.
Using a Surform blade, remove any bumps and roughness created by the cutoff tool. The final step is to create the shape you originally planned trimming with a series of contoured loop tools (figure 13). I carefully choose tools that allow me to create the right curve at the bottom, and I also trim the whole piece again right down to the rim (figure 14).
The last tool needed to finish is a metal kidney. Trim the final unevenness away and follow with a damp sponge and a plastic kidney to compact the clay.
By now the whole action becomes a fine balance between the character of the clay and the skill of the potter. If that stays in harmony, it is possible to create beautiful pottery.
Antoinette Badenhorst is a ceramic teacher, writer (in her mother tongue, Afrikaans), workshop presenter and demonstrator for more than twenty years. She exhibits her work in leading art galleries in South Africa, the USA and Japan. For the past twelve years she has worked with porcelain at different temperatures. You can contact her at email@example.com.
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