By nature, we potters are a utilitarian lot. We are makers, users, and re-users. Making the tools we use in our craft seems like a natural extension of that utilitarian outlook. As far as tools go, while I enjoy DIY projects, I’m admittedly a terrible carpenter. And so, in an attempt to keep my old barn studio a bit warmer in the winter months, I turned to foam insulation panels, which are inexpensive and easily cut with a utility knife. As I was eyeing the leftover scraps, I wondered how they would work as slump molds. As it turns out, they’re lightweight, convenient to store, and take the boring square-shaped slab, and elevate it with movement and form.
You can find the foam insulation sheets at most home stores. They come in different thicknesses; I’ve found the ½-inch thick sheets work best. Anything less than that and the foam isn’t thick enough to withstand the weight of a clay slab, and any more than that is too thick to cut through with a utility knife.
Considering Shape and Cutting Foam
Draw your templates on newsprint first. If you want your form to be symmetrical, folding the paper in half length-wise and width-wise before cutting helps in that respect. When designing my templates, I always keep in mind the size of my kiln shelf.
When tracing your templates onto the foam to prepare the cut, the size of your template will determine the size of your piece of foam. Larger pots will require more room around the edges of your cut-out, as you’ll need more support for heavier slabs.
Use a new blade in your utility knife. While the foam is very easy to cut, several cuts through with lighter pressure work better than trying to cut it all in one pass (1). Straight edges cut easily with a metal ruler, while tight curves may work better with a sawing up-and-down motion of the blade. Avoid sharp straight angles, as they tend to tear your slab. Tip: Don’t discard the piece you cut out. It can be used for pressing into a slab over a soft foam cushion, to make a shallow serving tray.
Depending on the depth you want for your finished form, the clay may need to stretch quite a bit, so I generally roll a slab with a thickness of 3⁄8–½ inch to start. I roll my slabs between two parallel sticks to ensure consistency (2). Flip it from the canvas to a ware board, then rib both sides of the slab in all directions for good compression. My favorite tool for this is a silicone rib found in baking sections of your local discount store. They’re large, inexpensive, and are designed for scraping bowls and cake decorating. They cover a large area at once and compress the slab well.
Slumping the Slab
Next, place your foam mold over your slab and board, put one hand under the board, one hand on top of your cut-foam mold, and flip the whole thing over sandwich-style. Put the whole sandwich flat on a table and remove the top ware board. Use kiln posts or something similar as props, laying them lengthwise under each side of your foam board, elevating the board 2 inches and supporting all sides (see figure 4). The foam will sag if the sides aren’t supported.
Taking a soft rubber rib, slowly coax the slab to slump by pushing gently around the perimeter of the form, then side to side, then front to back, creating a continuous, soft curve (3). If you have trouble discerning the outline of your shape, keep one hand underneath as a feeler, while the other hand is on top, tracing the outline with your rib. This should be a gradual process, slowly working the slab until it’s the depth you want. You can, at this point, trim off a bit of the clay around the shape, however, leave at least an inch all around to accommodate any additional slumping and/or shrinkage (4).
Throwing a Foot
While waiting for the clay in your mold to get leather hard, throw two open rings of clay on the wheel; one small for the foot, and one large for the sides of the platter (5). Throw both rings to have a slightly wider base. Make sure to taper the base, inside and out, so as to leave a small skirt of clay at the base to use as your attachment. Depending on timing, you may have to cover the rings with plastic. You want both rings soft leather hard when attaching them to the pot. At the time of attachment, they should be still quite pliable, but no longer sticky to the touch.
When the slab in the foam mold is leather hard, flip it out onto a bat or banding wheel, trim the edges to about a ¼ inch wide, and make sure the back is fully smooth by compressing it with a rubber rib. So as not to distort the edges of your slumped slab, fold a clean studio towel to support it underneath, inside the edges, while placing it on a banding wheel.
Removing the smaller ring from the bat, gently place and form it to the desired shape (6). Trace lightly around the foot, remove, score, slip, and put it back into place. With a rubber rib, press firmly around the base of the foot, compressing the clay, and adhering the foot to the base. Make sure to place your pot on a board at eye-level before going further to make sure your foot is level and flush to the surface.
Once the pot is turned over, reshape the towel to a doughnut shape encircling your foot ring and supporting the outer edges of your pot. Score and slip the edge of the pot and make one vertical cut in the larger ring to shape it to the sides of the pot (7). Firmly attaching the flared base of the sides to the pot, first, pinching it down between your thumb and forefinger, then rib it again to compress it. Rib from the upper sides of the pot, down toward the bottom, to emphasize a continuous curve, and so there is no visible demarcation between the bottom and sides.
To add a bit more movement to the pot, take a Surform tool and shave down each side toward the middle of the pot. This gives the ends extra lift and brings a lightness to the form. Finish the arc form with a final compression of the edges, giving a rounded smooth finish (8).
Joining together like, or even dissimilar shapes into one vessel can create entirely new shapes altogether. A single teardrop can be duplicated and joined together to produce a twin serving bowl, or even doubled again for a quatrefoil-shaped platter. Making your own molds can free you from the confines of the square slab and just may evoke new ideas, bringing new pots to your repertoire in the process.
Nancy Gallagher received her BFA from Kutztown University in Kutztown, Pennsylvania, and further studied functional pottery with Bill van Gilder. She works and teaches at her studio in Seven Valleys, Pennsylvania. To see more of her work, visit http://gallagherpottery.com.