We’ve posted a lot of handbuilding techniques on CAD that utilize various types of slump molds or hump molds. From plaster, to plastic, to bisque fired clay molds, there are lots of options for what kind of mold to use. But no matter what kind of mold you use, there is no rule that says you can only use it for the form it was intended for.
Brenda Quinn loves exploring new forms by mixing and matching techniques. In today’s post, an excerpt from Handbuilding Techniques, Brenda explains how to handbuild using a slump mold originally intended for a platter to develop a lovely vase form. – Jennifer Poellot Harnetty, editor.
Start with Slumping
To create this slab- and coil-built vase, you first need to cut an octagon out of paper to use as a slump-mold template. A variety of rigid materials can be used to make the mold, including cardboard, foam board, or wood. I often make molds out of cardboard and if I want to repeat a form numerous times, I use foam core, which is sturdier and holds up longer to the clay and multiple uses. When choosing what material to use for your mold, take into consideration the size of the cutout—the larger the cutout is, the sturdier the material should be. The forms I’m making are no bigger than twelve inches, and I often retire a shape after a few uses, making it unnecessary to use a more permanent material.
Next, trace the paper template onto your mold board, and allow at least an extra two inches of board around the cutout to provide support during the slumping process. Using a sharp knife, cut the shape out and mark the side of the board that you cut from—ensuring you use the side providing you with a more accurate shape. Find a bucket or box with an opening slightly larger than the size of your cutout, to support the edge of the mold as you work.
Make a slab that is at least five inches larger than the cutout. Tip: At this point you can texture your slab or to make it smooth. Carefully lift the slab and place it with the finished side facing down in the mold (figure 1). Trim away some of the excess clay, but leave an even ledge of clay about one inch wide around the edge of the cutout. This even lip helps the clay to slump evenly in the mold. If you leave too narrow a strip of clay, the clay may shift and fall into the opening during the next step.
Firmly grab the mold, slab, and support under it, lift them up, and tap it onto the table to force the clay further into the mold. Since we want an even, symmetrical, concave curve, tap it a few more times, then rotate the mold and tap it again. Repeat rotating and tapping until you reach a desired depth. The thickness of the slab you use, the plasticity of the clay, and the shape of the cutout determines the depth (figure 2).
Once the slumped slab reaches leather hard, put a bat on top of it and flip it over (figure 3). Cut away the extra clay and draw a line to use as a guide to cut the piece in half (figure 4).
Add Elements with Pinching and Coil Techniques
You can build onto the form using slab, pinching and coil techniques. Use a rasp to make 45° angles on the edges of the forms (figure 5). Score and slip along the edge of the pieces, lay one of the pieces with the concave side facing up on a piece of foam to support it and add a two-inch-wide slab of clay to the entire slipped and scored edge, except the longest edge.Pinching the slab ensures a strong connection and creates texture to contrast the smooth surfaces of the slumped slab or you can make a seamless connection and a smooth surface if desired. Use your fingers to form a corner at each of the octagon’s points (figure 6). Score, slip, and lay the other half of the octagon on top of the slab and repeat this same process (figure 7). Allow the entire form to stiffen under plastic. This helps to even out the moisture content and prevent the joints from cracking apart.
Next, turn the piece so it sits with the open side down. Score, slip, and add a coil to build the foot (figure 8). Make sure the foot is sturdy enough to physically and aesthetically support the weight of the piece.
After the foot stiffens, flip the vase over. Score and slip around the rim and add a thick coil. Pinch the coil to connect it to the base and to thin it out, moving the clay up. Continue adding coils and pinching until the piece reaches the desired height (figure 9).
Consider the Details From Start to Finish
Using a ruler, level out the top. Finish the top edge in a number of ways, such as the scalloped edge shown here (figure 10). I often consider the two-dimensional design on the surface when making choices about the three-dimensional aspects of a form. Knowing that I’ll be drawing a pattern that has a leaf image with a ruffled edge led me to choose a more organic edge for the top. Looking for ways to tie three-dimensional and two-dimensional aspects of a piece together can help bring unity to a piece.
Lastly, make and attach four small handles to the sides of the piece. Using small pieces of clay, I model four petals that are attached to the bases of each handle (figure 11). I like the way appendages add visual movement to a piece and also provide a place for an accent color when glazing. After these pieces are attached, allow the vase to dry slowly under plastic then bisque fire it.
Brenda Quinn teaches ceramics and visual arts at The Fieldston School in the Bronx, New York. Her work has been exhibited both nationally and internationally. She currently maintains a studio in her home in Mt. Vernon, New York with her husband, two daughters, three cats, and two guinea pigs. You can see more of her work at www.brendaquinn.com.
**First published in 2013.
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