Constructing and Carving Double-Walled Forms Katie Bosley Sabin

Appears in the Nov/Dec 2018 issue of Pottery Making Illustrated.

I’ve always appreciated ornamentation and its ability to elevate the ordinary into something magnificent. I’m driven to create work that’s beautiful in its precision and attention to detail and I approach functional wares this way, using my mark to transform the everyday object into something precious.

Double-walled vessels offer the complexity of form that I enjoy building as well as create a depth that pulls the viewer in closer. My decoration reflects my love of Islamic tile, Gothic architecture, and Art Nouveau details. I carve my designs into the clay to blur the line between surface and form and soften each line to a pillow-like finish to eliminate the sharp marks of the process. I aim to generate the experience I so love when viewing art—a sense of awe and appreciation.

Throwing

To create my double-walled cups with carved, suspended interiors and pierced exteriors I throw two separate forms that are embellished and then assembled. The size and proportion of these forms can be a fine balance. Too small and the inside won’t hold enough liquid, too large and the outside won’t fit comfortably in the hand. As you develop your own design, consider how the two layers interact both visually and physically.

Start by throwing an outer cup that is convex in shape. I often expand this form to its widest point in the bottom third and gradually taper in from there up to the rim (1). Throw the inner cup with a rounded bottom and angled wall that widens to its greatest circumference at the rim (2). This form should be approximately a ½ inch shorter than the outer cup to allow it to suspend when attached. It’s important to leave the walls a little thick, approximately ¼ inch, to ensure that the outer wall, with its pierced sections, can support the weight of the inner wall, as well as leaving room to carve either form without cutting through it.

Using calipers to measure the rims, throw these forms so that the inner cup is just barely too wide to fit into the outer cup. Imagine throwing a lidded jar with a lid slightly too big to fit. This minor overlap of rims leaves enough clay so that they will fit snugly together after being scored for attachment. This fit can be fine-tuned during trimming.

Trimming

Trim the outer form as you would a traditional footed cup, with two modifications. First, leave the foot wide, approximately ½ inch. Much of my process is done reductively, and width here allows for more options when creating a unique foot. Second, cut away the clay on the base of the inner form so it can be seen when the two pieces are joined together (3).

Trim the inner cup into a dome, following the contour of its inner curve. Imagine trimming a bowl without a foot. Remember to leave the walls thick enough to carve. This stage is the last chance to adjust the fit of the two forms and may require trimming extra clay from the rim of the inner cup. The two pieces should have a gap at the rims slightly under ½ inch when nested (4).

Preparing the Outer Layer

It’s crucial to keep the clay at medium leather-hard throughout the remaining stages. Be sure to spray the clay often and keep it wrapped in plastic whenever possible.

When developing a design, begin with the outer layer. Sketch design ideas out on paper first, keeping in mind that pierced elements should be placed at least ¾ inch apart so the structural integrity isn’t compromised. If the openings are small, you can include more; if they are larger, make fewer.

To transfer the design onto the clay, first determine the scale of the design, then how many times it can repeat around the form. Lightly draw vertical lines to divide the space into equal sections according to this (i.e. 6 repetitions=6 lines). I use an MKM Decorating Disc to do this with quick precision (5).

In one panel, draw the design, including pierced elements and any complementing lines that will be carved into the surface. Drawing a small X into the sections that will be cut away can help visualize the final effect (6). Freehand the design a second time in the next panel to ensure it will repeat well and provide enough space between openings. Using a banding wheel, add horizontal lines around the pot at all the points where lines intersect (7). This grid, which is erased later, allows for accuracy when repeating the pattern around the cup.

Next, draw and cut away sections to create a dynamic foot (8). Keep in mind that each new element should compliment any designs already on the cup. Be careful not to leave any section thinner than a ¼ inch, as this will make the piece susceptible to warping. Soften the cut edges using water, your finger, and a sponge.

Now cut out each pierced element with an X-Acto knife (9). Carefully bevel the cuts from both the inside and outside to create a tapered edge. I use a Kemper W23 Loop Tool, with an elongated loop shape, to remove the clay. I slide the side of the tool, rather than the tip, along the cut edge (10).

It’s important to note that I refine elements such as the foot and cut edges because I prefer a finished look that conceals the mark of the tool. I encourage you to find what finished looks like to you.

Preparing the Inner Layer

With the outside cup’s design drawn and cut, begin work on the inner cup. When making my pieces, I place converging lines on the inner form in the center of each opening in the outer form to create a dynamic interaction between the two layers. If you choose to do the same, identify where the middle of each pierced element will meet the inner form when they are attached. Currently the two pieces won’t fit evenly with one rim matching the height of the other (recall the ½-inch gap). Nest the cups back together and place a tick mark on the inner form, a half-inch lower than the center of each opening on the outer form (11).

With the placement of intersecting lines established on the inner cup, create a design around this, including a dynamic bottom. Draw and repeat the design using the same grid method described earlier.

Now carving begins on the inner cup. To achieve the pillow-like finish on my forms, every line is made and refined through a three-stage process. Start by carving a narrow V-shaped line. For this, I use Diamond Core Tools’ P1 V-tip Pencil Carver. Next, carve each side of the V wider with a loop tool (12). This creates a transition that can be softened using water, your finger, and a sponge (13). Switch to a paintbrush to soften any finer details.

Attaching and Completing

With the inside completed, wet and score both rims. With the two layers scored, enough clay is removed that the outer layer should slide all the way down to meet the rim of the inner form (eliminating any extra height) (14). If the outer form cannot slide all the way down, don’t force it, simply cut away any excess height from the inner form. Compress the seam together (15) and leave the form wrapped up in plastic for several hours or overnight, to allow the moisture level to equalize.

Once the seam has stiffened, use a metal rib to scrape away clay, primarily from the inside, to bevel the attachment point into a tapered drinking edge. It’s important that the double-walled form doesn’t feel any more cumbersome than a single-walled cup, especially at the rim. Remove tool marks using a sponge and a soft rubber rib.

Lastly, carve and soften the lines on the outer layer with the same methods described earlier. Soften the edge of each pierced element as well to create a consistent, finished look. Dry the finished cup slowly over many days (16).

To keep these delicate forms from warping, it’s important to fire them on shrink pads. To create a shrink pad, cut a small donut shape just wider than the foot of the cup from a thick slab of clay (17). This should be bisque fired, though it doesn’t need to be fired with the cup until the glaze firing.

Glazing

A simple, monochromatic glaze application complements the highly decorated surface and complex forms of my vessels. I use a palette of transparent glazes that pool in the carved lines. I suggest finding a glaze that behaves similarly. These double-walled forms can only be glazed by dipping, where the piece is completely submerged in glaze (18). Other methods risk leaving unglazed pockets between the two layers. I fire my work primarily to cone 10 in reduction. Larger or more precarious pieces are fired to cone 6 in an electric kiln, because the lower firing temperature means there is a lower risk of slumping.

Don’t forget to paint a thin layer of kiln wash on the donut-shaped shrink pad and fire the cup on it for the glaze firing to avoid warping. If the shrink pad is stuck to the foot after the glaze firing, a gentle tap of a hammer on the shrink pad should pop it off. For the final step, I smooth the foot of my pieces with a diamond sanding pad to create a polished look and feel.

Katie Bosley earned her BFA in ceramics form the University of Florida, and is currently an MFA candidate at the University of Nebraska, Lincoln. To see more, check out KatieBosley.com and follow her on Instagram @KatieBosleyClay.