Terra cotta corbels constructed using the right angle jig.

 Many years ago, while handbuilding a large form, ceramic artist Marcia Selsor was struggling to support two slabs that she wanted to join at right angles. So, she set out to build a custom tool to serve this purpose: a right angle jig to support the form in progress. The jig is a simple plywood structure that supports two ware boards at a right angle. Slabs are then placed on them and held in place during attachment. Over the years, it has proved to be an invaluable tool when building architectural or geometric forms, such as corbels, square tops of capitals or square vessels. Today, she shows us how to make and use her right-angle jig. Take it away Marcia- Jennifer Harnetty, editor.


Making the Jig
Begin with two pieces of 1/2-inch plywood cut to 12_15 inches. Cut a right angle shape out of each piece. To connect these notched ends, cut two 15-inch-long braces and one 14-inch-long brace from 4-inch-wide plywood boards. Attach the braces to each side and the middle (figure 1). Two sheets of plywood complete the jig (figure 2).

figure 1 figure 2

Using the Jig
Cut out all the clay pieces during the same session and store overnight
on sheetrock or gypsum board under plastic. Tip: Design tarpaper
patterns then cut and press them onto the slab. Use tarpaper patterns
much like sewing patterns but plan for the thickness of the clay. Store
and reuse tarpaper patterns.
Use a 45° bevel cutter to cut the edges of the shapes that will later
be joined at right angles. You can also use a cut-off wire held tightly
and pulled along the edge, or a fettling knife held at a 45° angle. On
the second day, or after the slabs have stiffened, score and slip the
edge of one and place in the plywood cradle. Score and slip a second
slab and slide it down to meet the edge of the first slab (figure 4).
Fill the seam with a coil and smooth with a rib.
To remove, tilt the whole works and slide the boards and slabs onto the
table. Gently pull the boards away from the clay, which
should stand free.

 

This post is excerpted from Ceramic Sculpture: Inspiring Techniques, which is available in the Ceramic Arts Daily Bookstore.

 
After joining the remaining two sides, attach the bottom, then attach
the other assembled sides to complete the basic form.

Remove from the jig and finish the exterior seams the same as the
interior seams. To work on the top and bottom, sandwich the form with
bats and flip it over.
Finish the surface with ribs or a
Surform tool.

For more great handbuilding techniques, be sure to download your free copy of Five Great Handbuilding Techniques: Variations on Classic Techniques for Making Contemporary Handbuilt Pottery.