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Firing exercises that test what your kiln can actually do
Five small firing exercises that each answer one question about your kiln, from a cone pack to a bisque test, with the temperatures they turn on.
Learning a kiln is not learning to press start. It is learning what your particular kiln does at particular settings, which is knowledge you can only get by firing it and writing down what happened. These exercises each isolate one question.
What to take away
- Fire the kiln empty once, with cones, before you trust it with work.
- A cone pack on every shelf tells you what the controller cannot.
- Bisque and glaze cones are different questions and deserve separate tests.
- Write down the schedule, the cones and the result every time.
Why the temperatures matter
Cone numbers are not arbitrary. Picking the wrong one wastes a whole load. A college chart of firing temperatures and cone equivalents sets out the practical ranges.
Bisque Cone Ranges by Clay
Clay type
- Stoneware, porcelain, mid-range
- Cone 08 to 04
- Low fire white, terra cotta
- Cone 02 to 1
- Raku clay
- Cone 04 to 1
- Crystalline glaze clay
- Cone 02 to 1
Bisque cone range
- Stoneware, porcelain, mid-range
- Low fire white, terra cotta
- Raku clay
- Crystalline glaze clay
Clays destined for crystalline glazes are bisque fired slightly higher than normal, cone 02 to 1. The same chart warns that above the point where low fire clays mature, those clays start to melt and damage shelves and other pots.
That last sentence is the reason studios forbid outside clay. A single low-fire piece in a high firing does not merely fail; it takes the shelf with it.
Five exercises
- Empty firing with cone packs on the top, middle and bottom shelves. Question: is my kiln even, top to bottom?
- Bisque test with six identical tiles, one schedule. Questiondoes my bisque reach the cone I set?
- Glaze thickness ladderone glaze, four dip times, on the tiles from exercise two. Question: how thick is right?
- Cooling testsame glaze, one load cooled naturally and one crash-cooled. Question: does cooling change my results?
- Full load versus half load, same schedule. Questiondoes the load size change the firing?
Each one answers a single question and none needs a finished pot. Run them in that order and you will know more about your kiln than most people learn in a year.
Five Kiln Test Exercises
- Empty firing with cone packsis my kiln even?
- Bisque test with six tilesdoes bisque reach cone?
- Glaze thickness ladderhow thick is right?
- Cooling testdoes cooling change results?
- Full versus half loaddoes load size matter?
What to record
| Field | Why |
|---|---|
| Date and schedule name | So a result can be repeated |
| Cone number set, cone bent | Heat work reached, not just temperature |
| Shelf position of each test | Where the kiln runs hot or cool |
| Total time and cooling time | Cooling changes glaze surfaces |
| Result and any faults | The reason the log exists |
Where to run these if you have no kiln
Community and campus studios will often fire test tiles for you, and their terms are usually clear.
One university craft center requires that all clay be purchased on site. Pricing includes glazes and firings, and no outside materials are allowed. It provides two electric bisque kilns and a cone 10 gas kiln. Orientation comes before open studio access.
After week 10 of the term, clay and greenware are not saved, regardless of labeling.
Running these exercises somewhere else first teaches you what to ask of a kiln before you own one. It fits around the setup work and the small projects that fill a shelf.
Common questions
Why fire the kiln empty?
Because an empty firing costs only electricity and it tells you whether the controller, the elements and the thermocouple agree with the cones. Doing that first avoids losing a load of work.
What is a cone pack?
Three cones set in a clay base: one below your target, one at it and one above. The pattern of which bent shows how far the firing actually went.
Do I need cones if my kiln has a digital controller?
Yes. The controller reports temperature at one point. Cones report heat work where you put them, which is the number that matters to the clay.
How many test tiles is enough?
Six per question. Fewer and one odd result looks like a trend.
