In the Studio: Make Your Own Kiln Setters Glynnis Lessing

Appears in the Jul/Aug 2017 issue of Pottery Making Illustrated.

When I first moved to Northfield, Minnesota, I found a wonderfully tight-knit community of potters. At that time, I was invited to fire with other local potters out at the old Halling Studio—named after Chuck Halling, who was a fixture in our pottery community until he passed away in 2006. Chuck was a very do-it-yourself potter and some of the handy things he made were kiln setters in custom sizes (1). I happily used his templates when I set out to make some for myself. These homemade setters are quite useful for fitting horizontal pieces, such as plates and trays, into taller kiln shelf spaces. I even use these in bisque firings to save space.

I have been using Chuck’s setters for five years now and he must have used them for at least 15 years or more prior to that, so these are long-lasting.

I have three triangular sizes that work wonderfully for standard plate sizes (as well as low bowls, smaller trays, etc.) and then the “ironing board” shape as I call it, for longer trays. You can make square setters, but the triangle-shaped ones don’t rock, use less kiln furniture, and are a bit more space efficient.

Equilateral triangles:

Small: 3∕8 inch thick × 9 inches per side

Medium: ½ inch thick × 11½ inches per side

Large: 9∕16 inch thick × 16 inches per side

“Ironing Board” shape: 9∕16 inch thick × 17¼ × 13½ inches

1 Chuck Halling’s 20-year-old, handmade mullite setters.

Mixing the Mullite Recipe

It’s important to figure out the minimum amount of water for the dry mix so that your final mix is not too wet (2). Start with a 4545-gram batch of the Mullite Setters dry mix (recipe on page 11) and add it to 32 ounces of water. Caution: Always wear a properly fitted respirator when measuring and mixing dry ingredients. Allow it to slake for one day, then mix the batch with a power drill fitted with a paddle mixer. Small amounts of water can be added as needed to make the mixture more workable. A good test to figure out if the body has enough water in it is to roll a small ball of it in your hands; if it cracks around the edges, it needs more water.

Once the mixture is combined and at a workable state, seal it in a bucket for a few days to allow all the particles to fully saturate.

Working with the Mixture

Next, wedge the clay (3) and run it through a slab roller. This body behaves much more like cement than clay, and a workable state means that it’s wet enough to be slightly jelly-like. After it has been rolled out in this wet state, it helps to let it dry a little bit between drywall boards (30 minutes to an hour) so that it’s a little stiffer when you cut it. Each size setter has a corresponding thickness, so roll out the largest slab first, then readjust the slab roller for each smaller type. The clay is so short (non plastic) that it’s difficult to keep the edges from slightly cracking. It helps to compress the slab by beating it with a paddle to prevent edge-cracking. Do this until it’s close to the right thickness, then run it through the slab roller again.

Now, very gently smooth and compress the slab with a rib, being careful to keep it even and not to thin it (4), then begin to cut out a shape, using a template with a fettling knife (5). It’s very important to cut from each of the edges toward the center so that the corners aren’t pulled out of shape by the knife. Cut a circle in the center for ease of lifting the setters and for better heat distribution during firing. Cut off the corners to prevent chipping and save space in the kiln. 

Tip: Wear rubber gloves when handling the clay body because it can severely dry out your skin.

Drying the Setters

Now comes the slightly arduous drying process. Sandwich the setters between cloth covered drywall boards to keep the slabs from sticking to the drywall (6). The cloths must be completely smooth so that they don’t mark the surfaces of the setters. If you don’t have a lot of drywall boards, you’ll have to stack them. On the first day, they should be flipped every 12 hours—a total of 2 times, and then once a day after that so that the drying is even. The drywall board tends to get very wet at the beginning, so if you can use fresh drywall boards after the first day, it helps the drying go faster.

After 3 or 4 days, you can take the setters out and dry them on an open grid (7). I use a sheet of egg-crate diffuser, typically found in drop ceilings, which can be purchased at any building supply store. The grid must be elevated off the table so that air can circulate underneath it. I used kiln furniture to prop it up and laid it on the most level surface I had, the floor. After they are fully dry, you can bisque fire them.

Firing and Using the Setters

When I was ready for my next cone 10 firing, I used them as if they were already high fired; setting pots on them and stacking them as I would in a regular kiln loading. This was a BIG MISTAKE. Sadly, they sagged in this, their first firing. I had assumed that, since the setters we have been using over and over for years don’t move during a cone 10 firing, that the bisque-fired ones would not move. I was wrong. I had to mix, cut out, and dry a whole new batch. This batch I bisque fired and high fired them standing on edge—they didn’t warp. Now your setters are ready to use in your next firing (8).

I recommend applying kiln wash to the shelves after they are fired. I found that without kiln wash, my Grolleg porcelain pieces stuck to the shelves. This didn’t happen with stoneware.

A special thank you to my kiln setter making partner, Barbara Zaveruha, https://zaveruha.com.Glynnis Lessing lives in Minnesota with her family. She is a full-time potter and teaches at Northern Clay Center. www.glynnislessing.com.