One of the satisfactions that I get from teaching pottery classes and workshops is when my students challenge me to come up with fun, easy, and creative clay projects to construct in class. In doing so, I try and limit the list of supplies needed to cut down on expenses. I enjoy scouting out local hardware stores, craft stores, grocery stores, dollar stores, and even thrift stores for inexpensive and easy accessible supplies. For this particular project, I found most of the needed supplies in a local craft store:
Pottery tools: needle tool or knife, metal rib, rolling pin
Hollow Styrofoam half ball
Small hand saw, jigsaw, or craft knife.
Newsprint or scrap paper
Clay bat or lightweight ware board
Making the Mold
To convert the Styrofoam ball into a mold, first cut a strip of paper long enough to fit the circumference of the exterior of the hollow ball from rim to rim. The strip needs to be anywhere between ½ inch and 1½ inches wide. The width of the strip will determine the size and depth of your mold. The wider the strip of paper, the narrower and more pointed the bowl will be. Cut out the strip.
Place the half ball rim-side down on a table. Tape the paper strip to a point on the ball’s rim, then stretch the strip over the dome to the opposite rim and tape it down. With a pencil, mark the Styrofoam on both sides of the paper strip (1). With your saw, cut along both lines you drew on the dome (2). The two outer sides will become your mold.
Temporarily tape the two sides together making sure to align the cut edges. On each of the two sides, draw small half circles so that there is now an oval drawn at the very bottom interior of the Styrofoam ball (3). Untape the two sides and use the hand saw to cut away the half circles.
Align the two sides back together, lining up the rims and the bottom oval cut outs. The results should form a nice oval mold with an oval opening at the very bottom of your new mold. Securely tape these two sides together (4).
Making the Template
The best way to fill the mold with clay is to cut two separate clay pieces to be joined together. To create a template for this, fit a piece of newspaper into the interior of one half of the bowl, making sure that it stretches from the rim of one of the butted edges along the entire seam all the way to the other rim. With a pen or pencil, trace where the paper meets the middle mold seam and the rim (5). Cut out the template. Place the template back into the mold and make sure it lines up with the mold seam and rim.
Making the Bowl
Line the inside of the mold with plastic wrap, taping the plastic to the outside of the mold so, that clay placed against the inside wall of the mold stays in place and won’t slip down. Also, make sure that the plastic doesn’t cover over the bottom oval notch of your mold. You want to be able to access that opening with your fingers later.
Roll out a slab big enough to fit two of your template shapes. Rib the clay smooth. Position the template and cut it out with a knife or needle tool. Flip the template over and cut out a second piece (6). Lay each piece against the mold wall and cut away any excess clay. Bevel the rounded side of both slabs. Score and slip one of the edges, then place both sides back in the mold and attach them together. Use a rib to make sure the seams securely adhere and that the clay fits nicely against the walls of the mold (7). If the seams between the two clay patterns are thin or not secure enough, you can press a clay coil into the join to strengthen it.
Place a small ware board or bat over the top of the bowl so that the top mold opening is completely covered. Place one hand over the ware board and one on the bottom of the mold and carefully flip it over. Remove the mold, then begin to clean up the outside of the bowl (8). Cut away any excess clay and press a clay coil into any thin spots along the seam without pressing too hard against the clay, then use a rib to smooth the entire outside of the bowl.
Concave (Dimpled) Floor
I have used two separated techniques to create a dimpled concave bowl floor. The first technique involves simply manipulating the clay from the bottom so that it creates the nice dimple. To do this, I replace the mold over top of the clay bowl. Using the hole on the bottom of the mold as a template for placement of the dimple, gently push the clay down into an oval shape following the outline of the opening (9). When you’re satisfied with the depth and shape of the curve, remove the mold. Wet your finger and run it along the outer rim of the dimple to create a flat ring around the dimple (10).
The second technique involves creating the dimple using a separate slab piece and attaching it to floor of the bowl. First, replace the mold over the clay bowl, then with a needle tool or a knife, using the outline of the oval mold hole as your template, cut the clay away to expose the opened hole. Roll out a separate clay slab large enough to cover the opened hole. Place the slab over the opened hole and gently push the clay down through the hole slightly so that it forms a dimple and makes a nice impression of the outline of the mold hole (11, 12). Remove the clay slab. Turn the clay slab over (you should see the outline of where the oval impressed the clay), then cut out the slab, keeping it slightly larger than the outline. Place the slab, convex side facing up toward you, inside the opening so that edge of the dimple fits against the outline of the opening. You can pick up the mold and work from the outside bottom to push the clay against that opened hole. Once it’s snugly fitted against the bowl wall, place a clay coil around the seam and work it in so that it connects the convexed clay and the bowl securely. Replace the bat over the bowl opening and turn the whole mold upside down again. Remove the mold and clean up the outside seam. Smooth the clay with a rib (13).
Place a bat over the dimple and rest it over the bottom of the bowl. Flatten it a bit with your hand, then use a level to make sure the bottom is flat (14).
Make Decisions About the Rim and Foot
When satisfied, replace the plastic lined mold (with the bottom oval uncovered) over the bowl and flip it back over. If I need to adjust the dimple on the bottom, I can lift the mold and make the necessary adjustments without warping the bowl.
Now, soften the edges around the bowl’s rim or alter the rim into your own unique creation. I have also had students place feet on the bottom to create a fun clawed bathtub bowl.
When you’re satisfied with all aspects of the bowl (15), let it slowly dry before bisque firing. You can even let the bowl dry inside the mold to keep the walls from warping.
Decorate as desired (16).
Ann Ruel is a frequent contributor to Pottery Making Illustrated. She has her own studio, Little Street Pottery, in Suffolk, Virginia, and teaches pottery for the City of Norfolk. She has exhibited her work in shows and galleries all around the US. For more information visit: http://littlestreetpottery.faso.com, http://artaxis.org/ann-ruel, and www.etsy.com/shop/LittleStreetPottery.