Published Dec 18, 2019
Even though you don't need to pull up high walls with a large platter, large wheel-thrown platters can be challenging, especially if you are small in stature. In today's post, Yoko Sekino Bove gives some great tips for throwing large platters. - Jennifer Poellot Harnetty, editor
To make the wide platter shown here, I used 25 pounds of clay and a 24-inch-diameter bat. Place a bat on the wheel head then wet the surface. Place a circle cut out from a shower curtain on top of the wheel head. Make sure the curtain fits tightly and there are no trapped air bubbles. The shower curtain layer removes the need for using a wire tool to separate the platter from the bat, allowing the clay to release more easily when it’s flipped over and ready to trim.
Place the clay on the bat and start beating it down to a mound shape while slowly turning the wheel. Use dry hands (figure 1) or a wooden paddle (figure 2) and apply even pressure.
Flatten the mound to create a cake shape about 3 inches high. If you want to have a high rim for a bowl shape, keep the mound about 4–5 inches high. The diameter of the cake shape will be the size of the foot ring of the piece (figure 3).
Using a wet sponge and wet hands, open the form. Leave about 1 inch of clay between your fingers and the bat. Once the center hole is created, pull out toward you while also pressing down lightly with both hands to create a flat bottom (figure 4). While you expand and compress the bottom, move your hands from the center to the rim, then from the rim to the center several times. This throwing back motion can redistribute the clay and make it even (figure 5). It takes several passes to fully open up the form. Finally, use a rib to smooth and compress the flat surface.
Once the bottom is open and compressed, start forming the wall. Pull up, compress the top, then move your fingers back down the vertical wall, compressing and essentially pulling down to keep it even. Keep the wall straight (figure 6). Leave enough clay on the rim, which will support the structure by tension.
Using a very wet sponge, slowly open the rim (figure 7). When you flare the wall out, start from the rim and move your hands down the wall toward the center to keep the desired angle and prevent collapsing. When deciding on the final angle, factor in that the rim will move upward as it dries. The opening angle will be 10 to 20 degrees steeper when dry. Once the form is thrown, leave it uncovered for a day or two, depending on the humidity. In drier regions it may be necessary to cover the rim with a ring of plastic to keep it from drying too quickly.
To trim the platter, you’ll need to flip it over. If it’s a low, wide form, trying to lift it off of the bat directly and flip it would cause extreme distortion, so sandwiching the piece between two bats works better. Tip:You may need another person to help flip the big platter onto the second bat to prepare for trimming. It’s better to ask someone to help you, rather than trying to do it alone and ruining the platter.
Place a foam sheet on the center of the platter for support while flipping it over. The foam should be taller than your platter rim in order to support it. Cover it with a second bat that’s larger than the diameter of the platter (figure 8).
Use a flat surface to help with flipping. Create a pivot point by having one edge of the bat remain in contact with the table. Hold the bats together tightly to prevent slipping, lift one side up and flip the bat sandwich over as quickly as possible, maintaining contact with the pivot point to help steady the process and take off some of the weight (figure 9). This works better than trying to flip it in the air. Peel the shower curtain sheet off.
Center the platter on the bat. Its own weight keeps it secured to the bat, so you don’t need to place clay coils around the edge. Trim the outside of the foot ring first to define the platter’s silhouette. The foot ring itself should be almost as wide as the rim, to allow for support. Sharp tools can reduce both the physical burden on your hands and the trimming time significantly. A center ring prevents potential sagging of the center part, so define that area, then trim away the excess clay between the two rings. The amount you trim away depends on the thickness of the bottom of your platter. For this platter, which started with a bottom thickness of 1 inch, I trim away about 2⁄3 of an inch of clay inside of each foot ring, leaving a bottom thickness of just over 1⁄3 of an inch. Make sure the inner ring(s) are not taller than the outer ring by checking with a straight edge (figure 10 and 11).
For hanging, carve a deep groove into the outside of the foot ring (figure 12). This is less stressful to the foot ring than puncturing holes. After firing, use a loop of picture hanging wire placed in this groove to hang it.
Flip the platter right-side-up using the sandwich method again and check the weight and appearance of th e foot ring. Before the platter reaches the bone-dry stage, flip the platter occasionally to let it dry out evenly and to prevent warpage. Never pick up the platter by the rim; it may cause warpage or cracks (figure 13).
- Always place a big platter in the center of the kiln for even heat distribution. The foot of the platter should be completely supported on a single, level, smooth shelf, otherwise, cracking and warping can occur. It may help to fire the platter on a thin layer of fine grog or on a waster slab made out of the same clay body to allow for lateral shrinkage during the firing. To prevent the rim from cooling off faster than the center part, which can lead to cracking as the rim contracts more quickly than the rest of the platter, evenly surround the rim with kiln posts. Alternately, when firing low, wide work, make sure there is adequate airspace between the rim of the platter and the shelf above it. Allowing air to flow freely helps to minimize the temperature difference between the middle of the shelf and the outer edge.
- Do not place objects on the platter during a bisque firing. This can cause it to warp or crack.
- Most of the center cracks happen during the cooling process. It will help big platters survive the thermal shock if you can slow down the kiln’s cooling process, either by ensuring the kiln is fully loaded, or by adding a down-firing ramp schedule to the end.
- Always use kiln wash and apply a thin layer of alumina hydrate solution to the unglazed foot ring. The weight sometimes makes a big platter stick to the kiln shelf during the glaze firing.
Yoko Sekino-Bové is an artist and instructor living in Washington, Pennsylvania. To see more visit yokosekinobove.com.
This article originally appeared on pages 17–20 of the May/June 2013 issue of Pottery Making Illustrated. To learn more about the magazine or to subscribe, visit www.potterymaking.org.