Kiln Shelf Loading Under a Deadline
A community studio has one 18-cubic-foot electric kiln due for a cone 6 glaze firing in 36 hours. The studio coordinator has 14 glazed pieces from students: six are wide shallow bowls (30 cm diameter, 6 cm tall), five are tall cylinders (28 cm tall, 9 cm diameter), and three are flat tiles (20 x 20 x 1 cm). Available furniture: four full shelves (60 x 60 cm), three half shelves (60 x 30 cm), and a set of 5 cm and 10 cm posts. A previous firing left a hairline crack across one full shelf, and the coordinator notes that the cracked shelf was used last time without incident. The kiln's usable stacking height is 60 cm. Two of the bowls have glaze pooled thickly at the foot ring and were not stilted.
1. Propose a shelf layout and stacking plan that fits all 14 pieces within the height limit, and justify your furniture choices.
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Start by calculating footprint demand. Each wide bowl needs roughly a 32 cm square zone to keep glaze clearance between neighbors, so one full shelf (60 x 60 cm) holds at most four bowls in a 2x2 arrangement, leaving margins. Five cylinders at 9 cm diameter can sit in a row on a half shelf with 3-4 cm gaps; three tiles fit on one half shelf with room to spare.
A workable plan: Level 1 (bottom, 10 cm posts) - two half shelves side by side carrying the five cylinders plus the three tiles. Level 2 (10 cm posts) - one full shelf with four bowls. Level 3 (5 cm posts) - one half shelf with the remaining bowl, centered for balance. Total stack height with posts is well under 60 cm.
Avoid the cracked full shelf entirely. A hairline crack can propagate under thermal cycling, and a shelf failure mid-firing drops ware onto lower levels. Even though it survived once, the correct judgment is to retire it from structural use rather than gamble on student work. Balance the load: do not place all heavy bowls on one side of a shelf, and keep tall cylinders off the top level where they could contact the lid.
2. The two unstilted bowls have thick glaze pooling at the foot. What do you do before loading, and why?
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Thick glaze at the foot ring will run and fuse the piece to the shelf during the firing. The correct action is to grind or scrape the glaze back to bare clay at the foot ring (a 3-5 mm clean margin), then wipe the foot and the shelf contact point. If the glaze layer is too thick to remove cleanly, the piece should be set on stilts or a waster slab so any run is captured rather than bonding to the shelf.
Reasoning: at cone 6, pooled glaze becomes fluid and will wick under the foot. A fused bowl either breaks on removal or damages the shelf, and shelf damage is a recurring cost. Stilting is a fallback, not a substitute for proper glazing, because stilts leave marks and can tip under a heavy bowl. The judgment call is to delay these two pieces if there is not time to correct the glaze, rather than fire them as-is and risk both the ware and the furniture.