People often ask me how I avoid cracking in my work, especially since I construct with both wheel-thrown and slab-built sections. Over the course of making similar forms repeatedly, I can now anticipate where my work will potentially crack. Now I add small coils or leave extra thickness in those areas to ensure a better attachment.
When I’m working out a new form, there are many renditions that end up in the reclaim bucket. Unfamiliar pieces tend to crack more because I’m unsure of the finished configuration, and I move the clay back and forth, often over straining the seams. Working with sections that have a similar dryness helps prevent cracking. Learning to cut, bevel, reattach, and thoroughly address each seam is the key to preventing a piece from cracking during drying and/or firing (see page 43).
The sauce boat is a perfect form to explore seams. It can be a variety of shapes and it’s made of multiple components—foot, wall, spout, and handle. The wall is thrown separate from the foot so I can alter it and attach to it in any configuration rather than sticking with the circular shape the wheel lends itself to.
Throw the Foot
Begin by throwing the foot. Center about 1¼ pounds of clay into a tight ball, then open it down to ¼ inch above the bat. When opening the clay, form a funnel or V shape (1). Keep the rim compressed as you raise the clay. Then, with strong pressure from the outside, begin to raise the walls, pulling up and out more than vertically. After several pulls the foot should have a distinct internal V shape—with an angle of around 90°. After the final shape is reached, use a flat-edged rib to clarify, compress, and smooth the wall all the way to the point in the center (2 and 3). Set the foot section aside to reach a trimmable leather-hard stage.
Throw the Wall
Next is the wall of the boat, which is a short, bottomless cylinder. Center about ¾ pound of clay and open all the way to the bat, compressing down right after opening. This is important as it adheres the clay to the bat. Begin to pull the clay outward about an inch or so, then compress it out and down to the bat again. Resume pulling the opening of the clay outward until it is 6–7 inches in diameter (4). If you throw a wider form, you will just have more material to practice with. If you don’t pause and compress the clay when pulling it outward, it will detach from the bat into a doughnut shape. Raise the walls to between ¾—2 inches depending on the size of the form. Shape the rim to your preferences. Lastly, scrape/sponge all the excess clay and slip from the bat and form. The wall will be ready to work with when it can be touched without showing fingerprints, but is still flexible enough to bend easily.
Trim the Foot
While the wall is drying, work on trimming the foot. I trim on a foam bat. The friction of the foam and my left hand’s downward pressure hold the form in place. Trim to the interior shape. After trimming, mark the shape you’re interested in on the face of the foot section with a pointed tool or pencil.
Attaching the Wall Sections
When the wall is dry enough to handle, cut the pieces of the wall and test them before slipping and scoring them into place. This helps keep symmetry and get the desired end result. Score along the planned outline in preparation for attaching the sections of the wall to the foot. Score all the surfaces of the wall that will be attached, and then begin to adhere them (5).
Once all the wall sections are attached, go back and compress all the interior seams with a rib or a rounded tool that will reach into any tight spaces (6). Then cut along the flange of clay remaining on the outside of the wall with a dull X-Acto knife (7). Note: It’s important to use a dull X-Acto blade. A sharp one will cut your hands and your canvas–covered tables. Dull blades cut through the clay just as well as sharp ones due to the thin nature of the blade. I usually make more than one pass to cut through the slab completely and so that extra clay does not hang and break off unevenly.
Next, go around and compress the exterior seams. Occasionally it may be necessary to add small coils to fill in gaps on the interior or exterior. If the line quality of the seam is uneven, use a rasp to remove clay, followed with a metal rib to smooth the teeth marks. Use the corner of a rib to compress the exterior corner seams (8). Go back and recompress all the interior seams again—the movement and pressure on the outside may shift the walls.
Adding a Spout
The spout is cut from a slab and beveled to attach to the corresponding bevel of the boat’s wall (9). Add a small cone of clay to each side of the spout to blend the fluid thrown lines with the cut slab spout (10). This added clay also strengthens an easily stressed area and keeps this seam from cracking. Add a simple strap handle. After the piece has firmed up, go over the whole thing and recompress all the seams once again, including the one around the handle. Finally, even out the surface with a green scouring pad and finish smoothing with a sponge. When you’re completely finished, lightly drape plastic over the piece so that it dries evenly.
Working in a Series
I frequently work in a small series—four to five pieces at a time works well. Too many more and I can’t keep up with the drying process. Working in a series leads to variation within the form (11). Seeing and responding to the changes within each piece helps me learn and grow. When I’m completely finished with a series, I lightly drape plastic over the whole shelf so they dry evenly.
Deborah Schwartzkopf is a studio potter living and working in Seattle, Washington. To see more of her work, visit http://debspottery.com Check out http://ceramistasseattle.info to learn about Schwartzkopf’s studio assistant program.