Thrown Slab Pottery - Thinking Inside the Box
At some point many years ago I realized all my pottery was round. Bowls, vases, plates—we all work hard to make our wheel thrown work perfectly circular. I craved a square. Slab work provided the outlet I needed.
Forming a slab is harder than most people think. A chunk of clay run through a slab roller creates a slab that can easily warp due to the singular direction in which the clay was formed. When you become serious about slab work, you need to throw your slab.
Start by cutting a chunk of clay. I like about a fifth of a bag cut off in a block. Drop each side-corner lightly onto the table to round it. This prevents the corners from trapping air as the sides are elongated into a slab (see photo at left). Slam a flat side of the clay onto a very sturdy table with a motion that moves the clay toward you as it hits. Reverse directions so you are holding the opposite side of the clay and repeat. Turn the clay 90 degrees and repeat until all four sides have been thrown. Then turn the clay over and repeat. Continue to turn and slam until the slab is about one inch thick.
Once stretched to this point, you can start to roll the clay with a rolling pin. Roll from the center of the clay out to each edge. Just as in wheel-thrown pottery, pressure is released as you near the edge of the clay. This prevents the edge from becoming thinner than the center. After rolling each edge, lift the clay gently, rotate it 90 degrees, and flip it over. You will notice that lifting stretches the clay as much as rolling does. Roll from the center to each edge, lift, rotate, and flip. Repeat. The combination of rolling and lifting from all directions creates a slab that will not distort in the fire as a machine-rolled slab often does.
Clay takes a lot of pressure to roll. You need the old fashioned rolling pins that can stand heavy use. In addition, take notice of the surface you are using. A fabric-covered pottery table will work, but it textures the clay and reduces the desirable stretch from lifting the clay. For good slabs, you need a large, smooth piece of wood, such as a quarter sheet of nicely finished plywood. I use an antique drafting board. Although it gets damp from the clay, the wood is thick enough to prevent warping. Of course, I never leave wet work on the wood for long.
The often quoted "dowel" method is less successful. If you place a dowel on each side of the clay just far enough apart to support the rolling pin, it will create an even thickness in your clay. However, your slab will be very narrow since it cannot be wider than the rolling pin, and you can roll the clay in only one direction. You might as well use the slab machine. Using a rolling pin to create uniform clay thickness is a skill that takes time, to develop, but luckily you can always practice by making cookies.
When the clay is just one lift from the thickness you want, lift and place the clay on a surface to dry to leather hard. I use newspaper laid flat on my cement floor. Newspaper is big, readily available, and allows me to turn or move the slab as needed without stretching the clay further. It also allows the clay to move as it shrinks during drying. This prevents cracking and stress points. However, newspaper does create small flaws on the back of clay where the paper has creased. If this is a problem in your work, newsprint from a large roll is an ideal option.
Templates are the pattern used to cut the pieces from the slab. A template can be made from paper, but pieces cut from cardboard can be pinned or taped together to make sure they create the three dimensional shape you want before you cut any clay. When the slab is leather hard, arrange the template pieces on the clay to make the best use of your slab. Start by cutting the walls. I use a pin tool to cut the clay. For smooth clay types, an X-Acto knife provides a more precise cut. It is important for the tool to stay vertical as you cut. This creates a nice straight edge.
Next, join the wall pieces together. I am a firm believer in scoring the clay, then adding a drop of water to the scored areas before joining. Slip does not work well with the heavily grogged clay I use, such as Big Pot. On the other hand, if you use porcelain, Tom Coleman swears no scoring is needed. Just slip and stick. After reading Tom Coleman’s recommendation, I thought I would try it on my clay. I created a three part vase and joined the parts with slip. After bisque firing, I was lifting the vase from the kiln when it separated into its parts, one of which fell back into the kiln and broke three perfectly innocent boxes. I have been a proponent of "score, score, score, score" ever since.
When your walls are joined, choose an un-textured portion of your slab, slightly larger than needed for the bottom of the piece. Dip the bottom of the walls lightly and quickly into water, then gently stamp the bottom slab. This will leave a water mark where you need to score the bottom in order to join it with the walls. Once joined, trim the bottom slab and you will always have a perfect fit. For reinforcement, score the inside corners of the pot, and press a small coil of fresh clay firmly into place. The larger the pot, the more important reinforcement becomes.
At this point, the form is ready for a lid. Add a slab to the box in the same way the bottom was joined. Then cut the top inch off the form with an X-Acto knife, and add a flange inside to hold the lid in place (see photo at left). Coils can also be added to reinforce the top joints.
Once the main form is complete, add details such as feet, handles, etc. Although I had a simple box in mind as I outlined this process, I use the same techniques on my most complicated stacked-box forms. With this method my work quickly found all sorts of new shapes, none of which are the least bit circular.
Last month, I found myself trying a new shape with slab work. It wasn’t until the day was over that I realized I had made a perfectly circular piece that looked exactly like it came off a wheel. Oh, well. All my pottery is square. I have been craving something round.
Submitted to the Spring 2005 Newsletter by Dawn Atkin