The opposite of the additive process of sculpture, the subtractive sculpture technique involves removing material to create a finished work. In ceramics, this technique is most often used for sculpture but functional potters can also have fun with it.
In today’s post, an excerpt from the April 2019 issue of Ceramics Monthly, Jessica Cabe shares how Zac Spate uses the subtractive sculpture technique to make his sweet little box forms. I love how these organic forms are enhanced by the wood firing. – Jennifer Poellot Harnetty, editor.
How to Do Subtractive Sculpture
To create one of his carved boxes, Zac Spates begins by wedging an 8-pound ball of clay. He shapes the clay to a rounded cone (1). After shaping, he runs a metal rib against the surface, holding it perpendicular to the clay to tear it (2). He formulates his clay to be fairly short and non-plastic so it tears easily. Then, he makes slight cuts, in this case on the top and the side, with a fettling knife to further shape the clay. He does not cut all the way through, but instead tears off the partially cut piece of clay (3).
After finishing the surface treatment, Spates cuts the top and bottom of the box apart, using a pair of bricks to guide his cut-off wire through and create an even, straight cut (4).
Once the piece of clay has stiffened up and the outside is hard enough to preserve the texture he created when the form is handled, Spates hollows out the two pieces. He makes an initial carving to outline the top of the walls with a trimming tool (5). He then uses a circular loop trimming tool (see this article for instruction on making your own clay trimming tools!) to continue the process of hollowing out the form, and eventually smooths the walls to blend in all of the trimming cuts (6).
Since this piece is not thrown and the clay is fairly short, Spates uses a wooden rib to compress the bottom, inside and out, to prevent cracking (7).
Next, Spates rolls out a slab that is about 3∕8 inch thick and cuts a 3∕4-inch strip to attach to the top piece to form the flange for the box. He uses the wooden rib to smooth out the transition between the outside edge and the flange, and his finger to smooth the inside of the clay strip to attach it firmly to the inside of the box (8).
Spates has now completed the form (9). Notice the slight difference of the surface and how the rough edges have been slightly compressed as he worked on shaping the interior. He usually tries not to touch the outside of the piece after he textures it, but as he hollows out the inside of the piece while resting it on foam pads, the texture slightly softens in the process.