Published Aug 10, 2016
Potter Ann Ruel says that, although it was the mesmerizing spin of the potter's wheel that originally drew her in to pottery, she soon felt she needed to break those circular boundaries. So she started altering her pieces into more complex forms.
Today, we present a technique Ann uses for making interestingly shaped press molds out of plywood. These slump and hump molds can create endless new possibilities for new forms for your pottery. - Jennifer Poellot Harnetty, editor
To create asymmetrical pottery forms, I developed a stacked plywood
mold-making process to create slump and hump molds using a wood
construction technique I learned from Dewane Hughes at the University of Texas at Tyler.
The tools and supplies for this technique are available at any local home center (or they may already be in your garage!).
- 1/2 inch plywood (flat and not warped!)
- Drill bit (wide enough for jigsaw blade to slide through)
- Wood glue
- Jigsaw with wood cutting blade
- Masking tape, Utility knife
- Angle Grinder (I use a 41/2 inch grinder) with sander conversion kit
- Wood screws - 2 and 3 inch
- Wood clamps (optional)
- Painting canvas with a liner backing
- Safety equipment (gloves, mask, ear protection, goggles, etc)
- Handheld drill
- Staple gun with 1/4 inch staple
Creating Your Design
This mold design consists of layers of contoured plywood glued up in a stair-step fashion, which is then ground smooth. When designing and constructing the mold, work from the top layer down, keeping in mind that the mold remains open on the top and bottom. Sketch out some shapes that you want to use and cut out a template. The shape you settle on becomes the top rim of your finished vessel. For your first mold, create shapes that have wide sweeping curves and avoid tight curves because they're hard to cut and sand.
Trace the shape onto a panel of plywood (figure 1) located so you have two to four inches of wood around the shape. The extra wood provides more gluing surface as well as rim support.
Drill a starter hole for the jigsaw blade close to the inside of the line you drew and then cut out the inside of the contour using the jigsaw (figure 2). Mark which side of the plywood is the "TOP" and label this sheet as "Layer #1." Use a pencil or marker to make registration marks on the outside edges of the plywood rectangle so that when all the layers are finished, you'll remember how to lay them together.
Creating More Layers
Place Layer #1 over the second layer of plywood and trace along the outside perimeter of the rectangle and the inside of your cut-out shape (figure 3). Take your ruler or compass and mark new measurements to the INSIDE of your traced shape (figure 4). There are no exact measurements. The specifications depend on the form you design.
Cut the second layer, remembering to label the plywood appropriately. After you've finished, stack the two sections together again and once they are properly aligned, extend the registration marks you drew on the edges of the first piece down onto the second one. These marks help you line everything up quickly when you're assembling the whole thing to glue it together. Continue following this process until you have reached the bottom layer of your form.
Gluing the layers
Before you glue the sections together, do a dry run to make sure everything lines up. Arrange the layers, with the top being layer #1, down to the bottom in the order they were cut. Remember to keep an eye on the inside borders, making sure they are lined up the way you want them. They should appear as "stair steps" (figure 5). Don't worry if they are not perfectly aligned, as you'll eventually sand them flat. Apply a generous amount of wood glue in between the layers (figure 6). Use masking tape to hold the layers together so that they don't slide out of place. Then, if you have wood clamps, use them to apply pressure to the stack so that a tight bond is formed or drive wood screws tightly into the corners of the stack.
Refining the Shape
Once the glue has dried, use the angle grinder to flatten the inside edges of your mold. To adapt the angle grinder for this purpose, you need to attach three things to the head of your grinder: the backing disc, gritted disc and the special nut using the illustrations from your Sander Conversion Kit. If you don't have a grinder, you can use a Surform tool and a little elbow grease to get the contour.
SAFETY IN THE STUDIO!
When using the grinder or any power tool follow all manufacturer's recommendations for safety including proper clothing and eye/ear protection.
Prop the edges of your mold off of your work surface using plywood scraps so that you don't accidentally hit the table surface with the grinder. Slowly begin grinding down the stair steps so that your layers meld one into the next. The grinder is a very aggressive tool and if you are new to using it, you may gouge into the surface. Don't worry if this happens, you can always apply wood filler to smooth out those areas.
Finishing the Mold
Line the inside of the mold with painters canvas to cover up the wood texture (figure 7). The canvas also allows clay to easily release. Stretch the material tight and flat while stapling to the top and bottom of the mold. Cut darts in the canvas to help it conform to the edges.
Ann Ruel is a potter living in Chesapeake, VA. She's a member of Ceramic Designers Association of Hampton Roads, and shows her work in galleries across Virginia.