Tumble Stacking a Kiln

Porcelain covered jar, 10½ in. (27 cm) in height, Dave’s porcelain, Mel’s Orange Underglaze dipped on the lip and applied as dots, Red-Black Glaze on bottom third, Rutile Base glaze (applied last), fired to cone 10 in reduction, homegrown bamboo handle, 2018.

I am a production potter with efficiency always at the top of my mind. Over the decades, I have learned to pack as many pots into my bisque firings as possible. I tend to tumble stack the top of my electric-kiln loads, as well as parts of my gas kilns when bisque firing. My approach includes laying forms over on their sides, placing pots within pots and pots on top of pots, and laying them on top of each other. This enables me to fit more wares into a given space, which means higher efficiency, lower costs, and more profits. 

A Strategy for Filling the Kiln Space

It’s easy to tumble stack pots within the confines of an electric kiln. My 10-cubic-foot Skutt kiln has one full bottom shelf and the rest are half shelves. I usually stack the kiln in a traditional manner about halfway to two-thirds of the way up for stability, then stuff the rest of the forms into the kiln via tumble stacking. You can stagger the shelves and tumble stack one side or the other or both, or choose to stack this way only in the top third of the kiln after using posts and shelves for loading pots into the rest of the space below. I often tumble stack pots on the top three shelves of my car kiln as well, but only on these top shelves because rolling the car vibrates the load and they can roll off the shelf.  

1 Mugs tumbled stacked on top of tumblers.

2 Square plate placed on top of tumble-stacked mugs, which are placed sideways on top of tumblers and lotion bottles standing upright.

3 Tumble-stacked mugs placed sideways on top of tumblers and lotion bottles, with square plates on top.

4 Three square plates were tumble-stacked as the top layer.

In addition to tumble stacking, I always fill the interior of larger forms with smaller forms that fit well. For example, I will place a tumbler inside a large mug and a sponge holder or soap dish into any pot that they fit into. In addition to tumble stacking and nesting pieces, I often lay forms on their sides on the shelf or on top of regularly stacked pots (or both) to fit more in any given space. You can mix forms, from platter forms to large forms to small forms, when laying them on their sides or standing them on end on top of shelves as well as when stacking on top of other pots. The best use of space is to have a variety of forms in terms of sizes when loading the kiln, that way they can fit within each other. I like making small pieces to fit into medium-sized pieces. Small pieces sell well, so I always try to have lots of them in every bisque firing. 

Learning the Limits of Tumble Stacking

My forms are all porcelain and are mostly wheel thrown, but tumble stacking can work with handbuilt forms as well. If you are using stoneware, you’ll need to keep in mind they need a bit more time at lower temperatures during the bisque firing to complete off-gassing, so dense packing in a kiln, including tumble stacking, may require a slower, hotter firing ramp to burn out impurities. 

5 Use a yardstick to make sure pots are below kiln-lid level to avoid breakage when closing the lid.

6 Laying down pots and nesting to use all the space for a bisque firing.

7 Tumble-stacked top-loading kiln with pie plates, spoon rests, vase, and mugs placed on top layers.

8 The top shelf in the car kiln with tumble-stacked square plates and pie plates on the top layer.

I mostly produce functional forms and need to get the most work as possible in every firing, no matter which kiln I’m working with. Over the years, we all learn that when stacking work, placing pieces on top of one another so they are touching foot-to-foot or rim-to-rim works fine, but with tumble stacking that’s all a moot point.
The idea is to get as much as you can in a given space, laying pots on their sides, nesting them, and stacking them on top of one another. You soon learn the limits you thought were true are not accurate. 

I tend to start tumbling pots on their sides on top of other pots that are placed standing upright, and then put platters or even plates on top of those loose, tumbled pots. You will need to experiment as every firing has different forms. In terms of weight limits, I have yet to have any pots crack from weight from forms stacked on top of them. I lay platters on mugs that are sideways. It’s best to have the touch points on the solid pot bottoms versus rims, but this has also proven less important than I thought. 

9 Alternate view of the top shelf in the car kiln with tumble-stacked square plates and pie plates on the top layer.

10 Car-kiln bisque firing with completed tumble-stacked top layer.

11 A car-kiln bisque load with a top layer of tumble-stacked mugs on top of upright mugs.

12 Car-kiln bisque load with a few top layers of tumble-stacked pots as well as layers of pots placed rim to rim (pie plates left and center) and layers with pots nested inside one another (bowls and small forms on the right).

The idea really is twofold, fitting more work in the kiln and giving up on the idea that pots need to be stacked rim-to-rim or foot-to-foot. You can lay pots on their sides in a few layers and top the tumble stack by placing a platter as the last layer with zero issues. The general idea is that in the top third of the kiln stack, I start tumble stacking on top of standing pots by first placing sideways pots and continuing up, with wide forms ending up on top, or lots of small pieces stuffed all around. 

As I am stacking this way in the top third of the kiln, and not tumble stacking a whole kiln, in my experience, it does not make a difference if I stack starting with the heaviest/largest/most sturdy form on the bottom to smaller, more fragile forms on the top. If you are new to tumble stacking, you may try this approach first to see how your clay body responds to stacking. Also, in my experience, the orientation of the form does not matter. A layer of mugs laid on their sides on a kiln shelf can support the same weight placed on top of them from additional stacked forms as a layer of mugs loaded standing right-side up. 

With this method of stacking, you’ll need to make sure your wares are bone dry so warpage is reduced. It’s best to not stack against the kiln walls, and I try to leave a small space, but occasionally I have to touch the bricks. I sight the top of my stack with my eye and fill the kiln to within ⅛ inch of the lid, fitting as much as possible. Laying a ruler across the top of the kiln can also help to gauge whether pots are stacked too high for the lid to close properly.

Salt-fired stoneware jug, 11 in. (28 cm) in diameter, stoneware clay, Blair’s red slip on shoulder, iron-rutile interior glaze, salt-fired to cone 10, 2017.

Porcelain mug, 5 in. (13 cm) in diameter, Dave’s porcelain, Red-Black Glaze top and bottom (applied first), Mel’s Orange Underglaze dots applied to the middle, Rutile Base glaze (applied last), fired to cone 10 in reduction.

Next time you are loading a bisque firing, give this stacking method a try and see if it can work for you. I’ve been doing it for many decades without any issues.

the author Mark Cortright is a production potter living and working in McKinleyville, California. He has been making pottery since high school, attained a BA in art from Humboldt State University in 1976, and has been a full-time studio potter since then. To learn more, visit www.LiscomHillPottery.com.


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