Have you ever thrown a lovely form to only find later that you have thrown the bottom too thin? If so, you know the feeling of being both frustrated and left with thoughts on how to fix it. Of course, the disciplined thing to do is to check the bottom with a needle tool before the first pull. But, in case you have forgotten to do so, here is a way to fix the base using a slab and a Giffin Grip.
There are a few ways to measure the base of your form. I usually use pottery calipers to ensure that the measurements are accurate. Flip the piece over and use the calipers to measure the diameter of the base (1). Make sure you are measuring from edge to edge of the base. Once you have the measurements, lock the calipers in place.
Throwing and Measuring the Base Slab
Once you have the diameter measurements, fixing the base of a pot can be simply done by rolling out a slab of clay or throwing a slab on the wheel. For the jar shown here, I threw a slab using ¼ pound of clay. Throw the slab about ¼ of an inch thick. After the slab is thrown, with the wheel spinning, hold the calipers over the center of the slab with one hand (the hand opposite of your writing hand). With the other hand, use a needle tool to cut the slab to the exact size by aligning the needle tool right at the edge of the calipers (2). Cut all the way through the slab to the bat. Cut away the excess and clean up the edges. Use a heat gun to dry out the slab a little. This process makes the slab easier to pick up off the bat, and it also helps to bring the slab to a drying stage similar to that of the form. With a wire cutter tool or fishing line (my preference), cut underneath the slab in preparation for removal.
Giffin Grip It
Use your Giffin Grip to center the piece with the base up and accessible for trimming. With your needle tool, trim away the thin base to remove it. Trim as close to the interior wall of the form at the base as possible (3). Now, slip and score the base of the form and the edges of the slab where you will attach the two. Attach the slab to the base and apply pressure to the attached area to ensure that the two pieces are joined. Use a small rubber rib to help smooth out the base and to compress the bottom (4). As this is done, the clay will expand a little beyond the edges of the pot. That is perfectly fine. Trim the edges and the excess clay off the base (5). Finally, use a trimming tool to refine and smooth out the base.
After you are done, stand the piece upright (6). Allow it to dry slowly by covering it lightly with plastic. Bisque fire the piece once it is fully dry, and then glaze it up.
Stephen Phillips is a ceramic artist from Crawford, Mississippi. He earned a BFA in ceramics from Mississippi University for Women. In 2015, he established Stephen’s Potter House Productions, a small studio space in the countryside of his hometown. Since college, he has had solo and collaborative exhibitions. See more on Facebook: Stephen’s Potter House Productions, Instagram: @sphouseproductions, and Etsy at www.etsy.com/shop/StephensPottersHouse.