Porcelain Slip Trailing

My pottery style has evolved over the years, but there has always been one constant: I have a passion for expressing traditional Japanese patterns on the surface of my pottery. To create the patterns, I’ve tried different techniques including applying multi-colored glazes, carving, etc. However, I’ve found that slip trailing thin lines using an applicator is a flexible and effective method that most boldly expresses the patterns I wish to show.

Throwing a Plate

Wedge a 3½ pound (1500g) porcelain ball for a dinner plate. I use a 12-inch throwing bat, and throw the rim to the edge of the bat in order to make a matched size set of dinner plates.

Instead of securing a platter with chunks of wet clay that could distort the rim, use a foam trimming bat to keep the plate from moving once it is centered. Tip: Use a Sharpie marker to draw circular guide lines on the foam trimming bat so that it’s easy to place forms on center. When trimming, leave a small circle of clay to carve a design inside of it (1). Using a ruler, trim the bottom foot ring of the plate to the desired size (2). Trim other pieces to the same diameter to make a set of dinner plates.

1 When trimming, leave a small circle on the bottom to carve a design inside of it.

2 Measure the diameter of the trimming line. Repeat to ensure the same size on other plates.

Slip Mixing

Clay slip can be created by using scraps collected from the bottom of your throwing bucket. Recycled clay can also be used if soaked in water until dissolved. Use an electric hand mixer and add clay or water to the mixture to get a pancake batter-like consistency that will flow through the thin tip of an applicator bottle. Screen the slip to remove any thick chunks that will cause the applicator tip to clog. Store any unused slip in an airtight container. Both porcelain and stoneware can be used as slip material if they’re properly mixed and screened.

Slip Trailing

Just before your plate becomes leather hard—the point at which you can pick it up without contorting the shape—is a good time to apply the slip. If you apply slip on a wet piece, it could collapse due to the added moisture. I use a Gaunt Needle Tip Applicator (3) (available on amazon.com). There are two sizes, 16 and 18 gauge. I find the 16-gauge needle suitable for slip work and the thinner, 18-gauge needle suitable for squeezing underglaze. Besides the applicator, it’s helpful to keep a small bucket of water, a wet sponge, and a thin brush ready by your side.

To fill the slip-applicator bottle, remove the threaded cap and squeeze the bottle hard while submerging the opening in a container of slip. Then, release the pressure on the bottle to suck the slip into the bottle. Tap the bottom of the bottle on a table to force all the material to the bottom. Then, squeeze the top part of the bottle, forcing out any air, and dip the opening into the slip again to completely fill the bottle. Repeat this multiple times, if necessary, to force out any air and completely fill the bottle.

Once the bottle is full, use a wet sponge to clean the bottle top and screw on the needle applicator cap. Practice applying slip on a test surface before applying onto your pottery. Because I’m right handed, I find it easiest to draw slip lines from left to right while rotating the plate according to the design being applied. While using the applicator, a small chunk of clay may accumulate on the needle tip. Wipe the tip off with a wet sponge from time to time. Refill the applicator bottle often, the fuller the applicator is, the easier it is to apply a slip trail.

3 This is the Gaunt slip applicator I use for trailing patterns into my functional pieces.

4 Draw each oval chain shifted by one half of an oval link from the previous chain.

5 Draw the second oval chains 60° diagonal to the first series of chains.

6 Finish the second series of oval chains, working from the center to the rim.

Patterns

In this example, I create one of the more popular designs in Asian patterns: the flower of life. Start by drawing a straight chain of oval links, then, add more chains parallel to the first chain. The start of each chain is shifted by ½ of an oval link from the previous chain (4). After the first set of parallel chains is complete, another set of parallel chains is created by drawing chain-link ovals that connect the nodes of the first set of parallel chains (5, 6). Next, fill in the chain-link ovals between diagonal nodes, creating star-shaped patterns with spokes separated by 60° (7). If the drawing goes wrong, simply erase it with a thin, wet brush and reapply (8). Tip: I hold the applicator in my hand and squeeze with my thumb. When my thumb gets tired, I switch to using four fingers. After the patterns are complete, the plate is left until it’s bone dry. Then, wipe with a damp sponge to remove any edges and smooth out the slip drawing (9). You cannot use this cleaning technique on stoneware clay bodies because wiping with a sponge would bring grog to the surface.

7 Fill out the third oval chains starting at the nodes between the previous two.

8 Fix undesirable lines immediately with a wet, thin brush.

9 Run a slightly damp sponge over bone-dry greenware to remove any pointy edges.

10 After bisque firing, apply a red-iron-oxide wash over the slip-trailed pattern.

After bisque firing, wash the plates and let them dry overnight. Once they are dry, wax the bottoms of the plates. Tip: I mix a few drops of food coloring into my wax for visibility, and use pencil marks as a guide to denote the edges of the waxed area. To create a rustic shadow on the plates and to highlight the slip-trailed pattern, mix 10% red iron oxide into water and use a large calligraphy brush to apply it over the slip design (10). Now, remove the red iron oxide with a damp sponge, frequently rinsing the sponge in water (11). Finish by spraying with a glossy glaze and firing to cone 6 in an electric kiln.

11 Remove the dried red-iron-oxide wash with a damp sponge, rinsing the sponge often. Leave some wash in the crevices.

Dinner plate with hexagon flower pattern, 10 3/8 in. (26 cm) in diameter, wheel-thrown porcelain, fired to cone 6 in an electric kiln, 2019.

Deep bowl with feet, 11 1/2 in. (29 cm) in diameter, wheel-thrown porcelain, fired to cone 6 in an electric kiln, 2019.

Ai Yamamoto received a BFA from the University of the Arts in Philadelphia, Pennsylvania, and completed a post-baccalaureate program at Michigan State University. She has been a studio potter since 2008 and sells her pottery at local galleries and stores, and online at www.etsy.com/shop/curlyai.

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