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by Lauren Sandler
PotteryMaking Illustrated | January/February 2009
Bowl forms are particularly interesting for decorating because they provide an expansive landscape to explore. A generous open object when functioning, bowl acts as an offering yet also as an object of containment—a reservoir of reverie and reflection. It’s this paradox of offering and containment that I find most alluring and attempt to expand upon with my surface work.
(diagram description: Bowl, 12 in. (30.5 cm) in diameter, earthenware with terra sigillata and glaze, fired to cone 03.)
Making the Mold
Begin by making a clay mold that will be used to drape a slab over. The mold will be used to make the bottom quarter of the final bowl form that will then be built up to the finished shape and height with coils. The mold is made upside down and solid—later it will be turned upright and hollowed out. I start by drawing a boundary line to follow by first cutting out a paper pattern for what will be the top of the mold (when upright) and outlining that on the bat (figure 1). I begin the mold with a large thick slab, cut around the drawn line then add and remove clay as needed to create the desired form (figure 2). Take your time in shaping the mold; even out and smooth the surface with a Surform tool or rasp, then refine the shape and the surface with metal and rubber ribs. Place a bat and a torpedo level on top of the form and make any adjustments needed until it is level (figure 3).
Once the mold has set up to a firm leather hard (wet enough to hollow out, but firm enough to hold its shape when handled) turn it upright and examine it. Check the
shape to assure that the shape is what you’re looking for and add or remove clay as needed. At this point you can hollow out the form leaving 2-inch thick walls (figure 4). Once finished, let the mold dry for a few days. The mold doesn’t have to be bone dry before using—just dry enough so the slab won’t stick to it.
For a longer lasting mold, you may want to make a plaster one; although I have been using some of the same bone-dry clay molds for a couple of years—that includes many moves. The edges will often chip, but I usually cut the bottom part of the slab off above the chipped parts so it doesn’t interfere with the form.
Using the Mold
Roll out a 1/8 inch thick slab that’s large enough to drape over the mold (figure 5). I usually make a slab large enough to get two to three pieces out of it. Don’t let the slab get too dry before using it or it will crack when draped over the mold. I prefer my slabs on the wet side—just dry enough so they won’t stick to the mold—I let them do most of their drying on the mold. Place the slab over the mold and shape it to the mold. Once the slab has stiffened enough to hold its shape, cut off the excess clay from the bottom using an X-Acto knife (figure 6).
Swiftly lift the slab up, loosening it from all four corners and stand it upright. Even the rim using a Surform and bevel the inside of the rim to prepare it for a coil (figure 7). Check the level of the pot again here. You may have to gently tap the pot on its foot to make sure it’s level. Wrap the rim with a damp paper towel and plastic to prepare for adding coils. Leave the bottom unwrapped to stiffen in order to support the weight of added coils.
Because of the setting up time needed in coil building, I work on many pieces at once, putting another slab on the mold right after I take one off. I can build this form in one day, but time varies depending on the size and complexity.
Preparing and Adding Coils
Roll out a large coil the length of the circumference of the pot’s rim. I use a thread to measure the rim and coil. Slightly flatten the coil with your hand and bevel the edge that attaches to the interior beveled edge of the pot with your hand or small rolling pin. Add the coil, overlap the ends a bit and cut through both. Bevel both ends and attach (figure 8). You don’t need to slip and score since the clay is wet enough to be blended together easily. Blend the coil to the interior of the pot first, then Surform the exterior where the coil and the wall meet to smooth it out and add and blend a small coil around the exterior (figure 9). Repeat these steps until you get the desired size.
Finishing the Rim
Once you have the desired height and volume, even out the rim with a Surform, then measure and mark the four corners of the rim using a string and ruler. Decide how much of a curve you would like and mark the lowest point on two opposite sides of the rim. Use the Surform to cut the clay away moving from one side to the other (figure10) to maintain the same amount of pressure. Once you have the curve defined, smooth the rim using your fingers or a rib. (figure 11).
(diagram description: Using a paper pattern, trace the out- Add clay to the mold, taking care to Smooth the surface, then level the line of the top of the mold. remain inside your outline. bottom of the mold. Hollow out the leather-hard mold, Drape a soft slab over the mold, com- Fit the slab to the mold, then trim leaving 2-inch thick walls. pletely covering it. excess clay with an X-Acto knife. Bevel the interior edge to prepare it Add a large, slightly flattened coil to Add a thin coil to outside wall where for an added coil. the rim and blend the interior seam. the larger coil and the pot meet. Remove clay down to your marks and create a gradual curve to the rim. Smooth out and finish the curve and Apply the base coat of terra sigillata soften the rim. using a soft brush. Apply the final layers of terra sigillata, incise lines, and add glaze details. The finished bowl, 12 in. (30.5 cm) in diameter, earthenware with terra sigillata and glaze, fired to cone 03.)
Finishing the Pot
My current surface work comes from the desire to use my pots as a space to abstractly render elements of my life, observations, and reflections. I’m interested in breaking up the surface of the form and creating spaces within and upon the object. The division of space through line and color provide symbolic opportunities to explore para-doxical states of interior and exterior, expansiveness and constriction, possibility and unattainability, connections and missconnections. Essentially the surface of a pot is a place where the inward and the outward meet, a means of finding connections through our shared interior worlds.
I prefer terra sigillata to glaze for its soft and non-reflective surface. I want to keep the surface in a raw state —as close as possible in appearance to unfired clay—for me that’s when the clay is most vibrant, when it most resembles skin and our bodies.
Before brushing on the sigillata I decide the design and general layout of the surface, how it will be divided, what colors I will use, where I want the red glaze to be, and how I want the dots and drips of red glaze to connect or disconnect. Although I make a lot of decisions as I am working, I do think about the relationship of the red dots and the corresponding line work, that being the central part of the surface design, and that which the rest re-volves around. I will consider the condition and position of the red dots – is there a tension between them? How will the lines move over the form? Will they connect on one side and disconnect on another? Will it be an isolated dot? Or a cluster?
I view the different sides of a form as passages of time, or spaces of transition, using color and line to establish the division or movement. Often a line may move in various directions throughout the surface, having to navigate in and around the different blocks of color. The change of color with incised lines along the borders conveys a shift between interior and exterior, creating channels for the line and dots to move through, come out of, or reside in.
My color choices vary, sometimes it is more of an aesthetic decision, which color is most pleasing or intriguing with the other, and other times it is based on contrast and I think more in terms of light and dark to make clear distinctions of surface
Once I decide the general layout, I begin by applying the base coat. I wait until the clay is bone dry before ap- plying the sigillata—if done earlier, the clay won't absorb the sigillata and it will take a long time in between coats to dry. I use a hake brush because it holds a lot of liquid, moves well on the surface and doesn’t leave brush marks (figure 12). I apply two to four coats of sigillata, depending on thickness; if it is too thick, the sigillata will peel off the fired surface. Let each coat dry before applying the next. After the final coat (of base color), but before the sigillata has completely dried—darker in color, cold to the touch, but not leaving any finger marks on the surface, I rub it using a small piece of foam until I get a shine to the surface. I prefer foam to plastic because it moves more easily across the surface.
The second color is brushed over the first, I start by using a thin brush to paint the outline then I fill in the spaces with a wider brush, usually two light coats and taking care not to apply it too thick, in order to avoid it chipping off after firing. This is followed by the incised line work using a pin tool and the application of the red glaze (figure 13). A clear glaze is applied to the interior of the pot after the bisque firing then fired to cone 03.
Clay, Glazes, and Terra Sigillata
Cushing’s White Terra Sigillata
Water . . . . . . . . . . . . . . . . . . . . . . . . . .14 cups
OM4 Ball Clay . . . . . . . . . . . . . . . . . . . . 1500 grams
Deflocculant ...................... 0.1-0.3 %
Colors: All oxide/stain measurements are for one cup of terra sigillata.
Mason Stain 6464 Zirconium Yellow. 2 tsp
Red Iron Oxide . . . . . . . . . . . . . . .2 tsp
Mason Stain 6464 Zirconium Yellow. . ;2 tsp
Mason Stain 6305 Teal Blue . . . . .2 tsp
Titanium dioxide . . . . . . . . . . . . . . 1 tsp
Chrome oxide . . . . . . . . . . . . . . . . 1/8 tsp
I don’t use a ball mill when making terra sig. I mix up the batch, let it sit for a few days than siphon off the top layer of water then, I siphon off the sigillata and put it in a glass container. When I use it, I mix one cup sigillata with the specific oxides. Be sure to wear gloves and a mask when handling oxides and stains.
I add about 2 to 1 teaspoon of gerstley borate to each cup of sigillata to lower the fluxing temperature. I find this helps with sealing the surface. It may affect the smoothness of the fired surface, in which case I use a 220-grit sandpaper over the pots after firing.
Red Glaze: Unfortunately I recently found out that the red glaze I have been using is no longer being made. I have yet to start using another – still watering down the bits of dried red glaze left, but in the past I’ve used Duncan 1206-Neon Red.
Clear Glaze: Spectrum 700 Clear;Clay: Archie Bray Foundation Earthenware
Lauren Sandler is currently an artist-in-residence at The Clay Studio of Missoula, in Missoula, Montana. Lauren holds an MFA from Penn State University and undergraduate degrees in anthropology and ceramics from Ithaca College and SUNY New Paltz. For more information, go to www.laurensandlerstudio.com.