One Kiln, Two Cones, Three Weeks to the Craft Fair
Ms. Okafor's high school ceramics class has 22 students and one kiln. The clay is a cone 10 stoneware; the studio glazes are commercial cone 6 dipping glazes, purchased by the previous teacher. This term she bisque fires to cone 06 and glaze fires to cone 6 to fit the schedule. Results: surfaces look dry and uneven, several bowls show fine crazing, and one mug handle separated cleanly at the join. Students scratch the rims with a fingernail and the clay still marks; a dropped cup breaks into sharp shards rather than denting. Three weeks remain before the school craft fair, and four students plan to sell mugs and bowls as food-safe ware.
1. Sort the observed symptoms by likely cause. Which point to the firing schedule, which do not, and what should be verified before any conclusion is announced to the class?
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The symptoms do not share one cause, and treating them as a single “kiln problem” would teach the wrong lesson.
- Fingernail scratch, sharp shard break, visible absorption: consistent with an underfired body. Cone 10 stoneware taken only to cone 6 never vitrifies, so it stays porous and mechanically weak. This is the firing schedule.
- Crazing: consistent with a glaze/body mismatch and with moisture expansion in a porous body. Even if it looks cosmetic, on functional ware it is a durability warning.
- Dry, uneven surface: most likely application - too thick, too thin, or uneven dipping. Blaming the kiln here would send students to the wrong fix.
- Separated handle: almost certainly not a firing fault. Look instead at scoring and slipping, joining parts of different moisture content, or drying too fast.
Before announcing anything, she should verify on neutral material: test bars from the same body, glaze tiles fired alongside student work, and cones placed at top, middle, and bottom of the kiln. Diagnosing on finished student work destroys the evidence and the students' work at once.
2. What should Ms. Okafor tell the four students about selling at the fair, and what options are actually available in three weeks?
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She should tell them plainly that these pieces should not be sold as food-safe ware. An underfired, crazed, porous body can absorb liquid, stain, and harbor bacteria, and the glaze fit is unreliable - “food-safe” is a claim with consequences, and this is the moment students learn what professional responsibility in a craft looks like.
Refiring is not a simple fix: cone 6 glazes taken to cone 10 will likely run off the pot, can bond to shelves, and may volatilize. Changing the body mid-term is not feasible either.
Realistic paths:
- Shift the fair inventory to non-functional work - planters, dry-goods jars, sculpture - labeled honestly as decorative.
- Sell only pieces from a properly fired, verified test batch, if one can be produced and tested in the time available.
- Reframe the booth as a process exhibit, with absorption data and firing logs displayed beside the work.
Whichever route she takes, she owes the students the reasoning, not just the ruling. A decision without the explanation is compliance; with it, it is curriculum.
3. Redesign the remainder of the term so that the failure becomes assessable learning rather than a lost batch.
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Change the production sequence and grade the process evidence:
- Fire a set of test bars from the class body; weigh, boil, and reweigh to record absorption.
- Run glaze test tiles through the same firing as the student work, every firing.
- Keep a firing log recording cones at top, middle, and bottom.
- Match materials - if the program must stay at cone 6, buy a cone 6 stoneware body. The fix is matching body to glaze, not more time in the kiln.
Assessment should weight the log, the test results, and the documented revision a student makes on the next piece, not only the finished pot. Add a short pre-loading check initialed by a student technician: cone, glaze rating, body rating, drying time.
This keeps the standard's real content - understanding how materials behave under specific conditions - and it gives the four students something to show at the fair that is honest about what happened.