Tips and Tools: Smooth Bottoms Jeff Campana

Appears in the May 2015 issue of Ceramics Monthly.

Other than a rough rim, nothing irritates a potter more than a ragged bottom. Attention to detail is important and when a pot scratches up a table or is simply uncomfortable to hold, more prudent measures should be taken. Here's one industrial solution you can try in your own studio.

Years ago, I realized the need for my work to have a smooth, polished, glass-like foot for the high craft, luxury sensibility I sought. Beyond just protecting furniture and looking nice, polished feet bring an entirely new experience to the use of the work. The sound and feel when a polished foot touches down on a table is distinctly different from that of an unpolished foot—a solid and resonating clank versus a dull thud. Once I achieved the finish using just wet/dry sandpaper, I knew there was no going back, and so the search began to find the most efficient way to get this surface.

Lap wheels used in glass studios are prohibitively expensive and overly bulky for a tool that only gets occasional use. Using sand paper or hand sanding pads was far too labor intensive and unpleasant for me to commit to indefinitely. My search eventually led me to the world of wet-air grinders. Native to the trades of concrete and stone countertop finishing, these tools are lightweight, portable, versatile, and durable.

A wet-air grinder is basically a pneumatic grinder with water running through its spindle. Because the tool is designed to be handheld and used with the cutting face pointing down, a few alterations are necessary to use it as a stationary tool with the cutting face pointing up. I built a wooden jig, coated in epoxy resin to withstand regular exposure to water, that firmly holds the grinder upside-down and horizontal (1–2). To further stabilize the grinder, I strap the entire assembly to a cement block. Because the tool casts off a great deal of water while running, I generally run it inside a deep sink (3). My simple solution to make it run continuously is to zip tie the handle down in the “on” position (4).

The specific tool I use is the Gison Wet Air Grinder GPW215. This is very well constructed, heavy-duty tool that can cost about $180. Mine has lasted years with little sign of wear. I chose it because of the high speed capability (11,000 rpm). While this is far too fast for my purposes, the gearing used to attain these speeds means that it will spin at lower speeds with much less air. I attach a regulator to the air line and run the tool at about 20 psi, which drastically reduces the amount of air used, thereby reducing the size of the required compressor. There are various polishing pads available for these tools (5). After trying a few different kinds, I have settled on JHX Plus 3-Step Wet Diamond Polishing Pads. In just three steps they can bring a foot from rough and crusty to a glass-like finish (6). They are white, which means they will not discolor porcelain. A set costs about $50 and will last for several years.

Additional Uses

By adding a turbo diamond cup wheel to it, I am able to clear a kiln shelf covered in flaky kiln wash and heavy glaze drips down to a bare, like-new surface in less than a minute (7). For this I am always sure to wear a respirator and eye protection.