Plaster and ceramics go hand in hand and it is what many potters use for a hump mold. Some potters prefer to keep plaster out of their studios and would opt for a bisque mold. But potter Lauren Sandler has been making hump molds for her work out of unfired clay. Yes, you read that right! Unfired clay! This way she doesn’t have to deal with the mess of mixing plaster, doesn’t have to wait for her molds to dry and be fired, plus, if she gets tired of the form, she can reclaim the clay for some other use.
Now, I don’t mean to diss our good friend plaster, but I do love the simplicity, speed, and versatility of an unfired hump mold. Check it out and see if you agree! – Jennifer Poellot Harnetty, editor.
Why Use Plaster for a Hump Mold When You Can Use Unfired Clay?
Bowl forms are particularly interesting for decorating because they provide an expansive landscape to explore. A generous open object when functioning, a 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.
Making the Hump 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 hump 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.
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At this point you can hollow out the form leaving ½-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 – and 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 Hump Mold
Roll out a 1/8-1/4 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 (figure 10) to maintain the same amount of pressure.
Once you have the curve defined, smooth the rim using your fingers or a rib. (figure 11).
For more information or to see more of Lauren Sandler’s work, please visit www.laurensandlerstudio.com.
**First published in 2015