How to Load a Kiln: Tips for Even Firings Every Time
You've wedged your clay, thrown your pots, let them dry, bisque fired them, glazed them carefully, and now they're ready for the glaze firing. The last thing you want is to ruin everything with a poorly loaded kiln. Kiln loading is a skill — and it's one that experienced potters develop over years. Here are the fundamentals.
Start With a Clean, Dry Kiln
Before loading, make sure your kiln floor and shelves are free of glaze drips, kiln wash flakes, and debris from previous firings. Any loose material can fall onto your work during firing. Brush out the kiln interior with a dry brush and vacuum if needed.
Check your kiln wash. If shelves look patchy or the wash is flaking, add a fresh coat and let it dry completely before loading.
Plan Your Load Before You Start
Don't just start placing pots and hope for the best. Look at all the pieces you plan to fire and mentally sort them by height. You'll want to arrange shelf heights to accommodate your tallest pieces without wasted vertical space.
A well-planned load uses every cubic inch efficiently. A poorly planned load leaves gaps you can't fill because you didn't think ahead.
The Spacing Rules
During a bisque firing, pieces can touch each other — they won't stick because there's no melted glaze involved. You can stack pieces inside each other (bowls nested in bowls, for example) and fit significantly more into a load.
During a glaze firing, pieces must never touch each other or touch kiln shelves with their glazed surfaces. Melting glaze will bond pieces together permanently. Leave at least a quarter-inch of space between any glazed surface and another object.
The bottom foot of every glazed piece must be completely free of glaze — wax resist is the easiest way to ensure this.
Position Your Best Work in the Middle
The middle of the kiln — vertically and horizontally — tends to fire most evenly in a top-loading kiln. The top and bottom of the kiln can be slightly hotter or cooler depending on the kiln's element configuration. Put your most important or most glaze-sensitive pieces in the middle.
Witness Cones: Always Use Them
Place a small cone pack (three cones — one cone below, your target cone, and one cone above) on a bottom shelf visible through the peephole. After firing, these tell you exactly what temperature was reached, independent of your controller's reading. If your controller says you hit cone 6 but your witness cone shows otherwise, you have a calibration problem.
Never Rush a Cold Kiln
If your kiln has been sitting cold in a garage during winter, or if you've just moved it, give it a very slow initial preheat — even a candling period at 200°F for an hour before beginning your firing program. Cold kilns and cold kiln furniture hold residual moisture that needs to escape slowly.
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