When most people think of ceramics sanding is not the first thing that comes to mind. Yet, it is really an integral part of the ceramics making process. I have fuzzy memories of the first time I learned about how my work could be smoothed of rough spots, but the first time I ever taught it to my own students is crystal clear.
It all started when one of my students asked about how to prevent the work he was making from scratching his table. I told him I would show him how to correct for that issue in the next class’ demo. I gathered up some of my own work that had recently been glazed fired, wet/dry sandpaper and a big bowl of water. At the time I had three classes back to back and I covered the pros and cons of sanding at each stage of the clay process. Other than making a mental note to include it again in future sessions, I figured that was that.
Boy was I wrong!
Apparently, my innocent little demo on sanding had spread like wildfire throughout the studio. Just like it hadn’t occurred to me before being asked, it hadn’t occurred to any other instructor either to cover with their class. The fact that those of us who sold our work sanded every single piece blew the minds of some of the studio members. Not in my class, these studio peeps didn’t get the benefit of the before sanding and after sanding work I passed around for folks to examine, leading one to ask my student, “Do you believe in sanding?”
It still makes me laugh to this day just thinking about it. The phrasing did and always has struck me as so funny that every time I sand pots I’m reminded of it.
So, why do I (or why should you) sand ceramic pots?
Basically, clay shrinks. My work, which is fired to cone 10 or 2365º, actually shrinks three times. First, during the initial drying process as the water evaporates from the piece before the first firing. Second, during the first firing, otherwise known as bisque, much of the organic materials burn away further condensing the clay. Last, during the glaze firing when the clay vitrifies and any porous aspects of the clay close up. It’s always startling to folks new to the medium how much smaller their work gets.
The shrinkage is important to note because modern clay bodies are typically not a single type of clay, but rather a mixture of various types combined to support easier construction. Oftentimes this mixture includes sand or grog (among other additives) to help provide strength during the forming process. Both sand and grog (which is pre-fired clay ground up) are already shrunk when they are added to the clay mixture. Each successive firing of a piece pulls back and condenses the clay and brings the sand and/or grog to the surface – hence the need to sand what otherwise seemed a smooth surface.
For the ceramic artists out there, here are some tried and true tips for sanding your work.
- Sanding greenware, or unfired clay, is usually not worth it since the piece is so fragile at this stage. If you feel you must, then the drier the piece the better. Be sure to do it in a well ventilated area, preferably outdoors, wear a dust mask and use scotch brite pads.
- Sanding bisque ware is typically only valuable if you notice a previously missed sharp or rough point on your work – remember it’s only going to shrink again in the glaze fire. Wet/dry sandpaper of typically any grit will work and be sure to get the piece and sandpaper thoroughly wet to prevent dust.
- Another good time to sand bisque ware is if you need to level the bottom of a piece. It is an ideal time since the partially fired work is still soft. Thoroughly wetting the sandpaper and the piece are necessary. Tape the wet sandpaper to a table if you have no one to hold it in place for you and move the piece back and forth to level.
- After glaze firing, sand the bottom or any raw clay portion of the piece using a rough grit wet/dry sandpaper (the lower the grit number the more rough). Be sure to get the piece and the sandpaper thoroughly wet to prevent dust. I do this even if I’m working outside so I’m not breathing in all of the dust.
- After glaze firing, sand over a glazed surface using a fine grit wet/dry sandpaper with a grit of 400 or higher. Using such a fine grit sandpaper will allow you to sand the glazed surface without scratching it. Again thoroughly wet both the piece and the sandpaper to prevent dust … did you get that part about preventing dust yet?
- Technically any kind of sandpaper will work, but wet/dry sandpaper is made to be used when wet and will last longer. Regular sandpaper will fall apart quickly when used wet.
Here’s a little behind the scenes of my own sanding process this week. I use a big five gallon bucket to wet each piece and the sandpaper before sanding and again afterwards to rinse the pots off. I typically let them dry overnight.