How to Press Mold a Large Bowl in Sections

Ann Van Hoey: 2014; The Earthenware Ferrari; object; earthenware and gloss paint; H23x40x30cm.; slab building and press molding

Those of you who are avid CAN readers may remember the work of Belgian artist Ann Van Hoey from a couple of years ago when she won the CAN People’s Choice Emerging Artist award. I was immediately smitten by her work.

In this post, an excerpt from the archives of Pottery Making Illustrated, Andrea Marquis explains Ann’s press molding process and how she creates such flawless surfaces in detail. – Jennifer Poellot Harnetty, editor


Hand Rolling Slabs

Van Hoey’s forms begin as slabs and she uses commercial clay straight out of the bag. She prefers the clay to be soft and it’s important that the clay be pliable but not sticky. After working with the Dutch artist Netty Janssens, she doesn’t wedge her clay, preferring to align the clay particles by gradually thinning the slab as it’s rolled out.

After every pass over the slab Van Hoey carefully pulls the clay up and off of the canvas to allow the slab to expand evenly and to allow the clay platelets to align, strengthening the slab. She then uses a soft red Mudtools rib to repeatedly smooth the slab throughout the rolling process. She carefully removes impurities and large grog particles as she makes her final passes over the slab. The clay slab must be perfect because most of her vessels are not glazed and the finished surfaces come from the fired bare clay.


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Filling the Mold

To create her vessel forms, Van Hoey pieces her rolled slabs into a half spherical plaster mold, usually 11–19 inches

(30–50 cm) in diameter, that she purchased from her local clay supplier. In preparation for construction, she works with a paper pattern, developed through trial and error, to approximately fill her mold. She first lays the pattern on the slab (1) and then over the mold, eyeing the shape of the pattern to fit the interior curve of the mold. Using a modified knife (see figure 4 inset), she cuts out a piece of clay that is approximately the same size and shape as the pattern (2). Next she uses a plastic circle with dividing lines as a guide to create marks on the top of her mold to aid in equally dividing the circumference of her vessel (3).

The mold and slab are cleaned and then inspected for contaminants and irregularities. As Van Hoey readies the cut piece, she flips and reverses the slab to ensure the perfect side faces outward and the finished surface is without imperfections. She carefully presses her cut slab into her mold; slowly expanding the slab into the curved shape (4). She notes that it’s important this be done gradually and she takes great care to rib the clay up and down, and then back and forth with horizontal strokes.

Next, she trims the slab, cutting it on the top edge with her modified pen knife that allows the blade to be inserted at an angle (5). She locates the dividing marks on the mold that were created with the plastic circle template. Using each mark as a guide, she draws a line in the clay with her knife that only goes halfway through the slab—this prevents scratches on the interior of the mold. Then she removes the excess clay (6).

Van Hoey uses a total of three slabs to complete her form. When joining two slabs she compresses the edge of the slab, beveling it with her finger in order to create more surface area for the thin slab pieces to connect. She scores the edges, taking care not to scratch the mold. With light pressure she uses her finger to feel where the slabs overlap and cuts the top slab to fit. She removes the leftover piece with her pin tool and applies slip to the bottom slab.

Next, she gently compresses the slabs together with her finger (7). Using a semi-circular custom-made rib that she cut out of an old credit card, Van Hoey repeats the above step with more pressure. During this process she removes a little of the overlap of clay to make the wall thickness uniform. After the clay has been carefully ribbed, she removes the top edge with her modified knife.

She repeats this process, rolling out slabs, cutting out patterned pieces, joining them and then refining the form to produce the sides of the vessel.

She fills the bottom by approximating the shape and repeats the above steps, beveling the edges and scoring the clay form in the mold. Before attaching the bottom piece of clay to the form in the mold, Van Hoey stamps the bottom of the slab with her chop (potter’s mark) and places the slab into the mold face down—this way impressing the stamp won’t distort the final form. Compressing the slabs together she repeats her refining and smoothing process (8). The refining process is very meditative. She notes that though it has been a slow evolution repeating the same technique, with practice she’s been able to hone and continue to improve her forms.

Van Hoey smooths the bottom of the form, then moves the mold onto a pottery wheel for more clean up. She centers it by eye, then secures the mold to the wheel head with clay wadding and continues to compress the clay form against the mold and refine the thickness of its wall. She trims the top edge of the vessel one more time with her altered knife and then compresses it with her finger to finish the top edge.

Removing the Vessel Form

Timing is critical for Van Hoey’s altering process. The clay must be at the perfect stage—firm enough to be handled out of the mold, but plastic enough to fold without cracking. The vessel shape must be evenly pliable so it’s important to avoid a draft that can lead to uneven drying. She lets her piece set up in the mold with a bat over the top and
places them in a cardboard box turned on its side. With the box closed, which protects it from drafts and helps to equalize the moisture in and around the piece, she lets the vessel set up for an hour or two.

Van Hoey removes the piece from the mold by flipping it upside down on a bat and gently tapping the mold to release the form (9). The upside-down form and bat go onto a banding wheel. Using the flat, wide side of a metal rib, she cleans the outside of seams where the slabs were joined together. She inspects the outside surface of the form for any irregularities—popping air bubbles and then using a red Mudtools rib to smooth the exterior surface (10).

Darting

Using her hands, Van Hoey flips the clay form right-side up and cradles it in a pillow. With her circular dividing tool (see figure 3), she establishes three equidistant points on the top edge of her form and makes a mark. Next, she measures how long she wants the dart to extend toward the bottom of the form as well as how wide she wants them to be, both of which will affect the final shape. These marks guide her as she cuts her darts.

With large, sharp, heavy-duty scissors, which create a cleaner, straighter cut, Van Hoey cuts through her form (11). She cuts next to the seams between the original slabs of clay used to make the form so that the seam will be underneath the dart and therefore concealed by it when the clay walls overlap. Next, she gradually folds and smooths the clay cuts to until they overlap. Then, with a needle tool, she marks the outline of the overlap. She scores and slips each side (12), making sure there’s ample slip in the corners of the overlaps, which keeps the darts from pulling apart.

**First published in 2015
Comments
  • Subscriber H.

    To really grasp what she does here, you should check out the video (link at the start of the article). You’ll see her use SCISSORS to cut her molded clay hemisphere, then overlap the darts to create her fascinating and lovely shapes.

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