Storage and Handling of a Drying Clay Body
A studio receives 50 kg of a stoneware body in 10 kg blocks wrapped in plastic. The studio is warm (26 C) and dry (30% relative humidity), and the blocks sit on an open shelf near a window. After a week, the outer 1 cm of several blocks is stiff and crusty while the cores remain soft. A student wants to wedge the crusty blocks and throw immediately. Another student plans to store reclaimed slop in a bucket with a lid but has been leaving it uncovered between sessions. The studio also has a plaster bat that has not been dried out and a bag of grog.
1. Assess the condition of the blocks and recommend a preparation method before throwing.
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The blocks are case-hardened: the surface dried faster than the core because of the warm, dry, open-shelf storage. Wedging alone will not fix this; it folds stiff crust into soft core and creates hard spots that throw unevenly and can crack in the bisque. The correct method is to rehydrate the crust: wrap the blocks in damp (not wet) cloth and plastic for 24-48 hours, or slice the blocks into thinner slabs, spritz, and bag them so moisture equalizes. Then wedge thoroughly and check by cutting a block open to confirm uniform color and firmness.
Prevention matters as much as the fix: store the body in a sealed bin or double-wrapped in a cool spot away from the window, and rotate stock. The grog is not a remedy for case-hardening; it changes the body's texture and shrinkage, so adding it to fix dryness would alter the clay's behavior.
2. Evaluate the reclaim and plaster-bat practices and state the corrections.
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The uncovered slop bucket is losing water to the dry air, so the reclaim will stiffen unevenly and may grow mold or skin over. Keep the bucket lidded and top up with water; stir periodically. When reclaiming, spread the slop on the plaster bat to dewater, but only if the bat is dry. A plaster bat that has not dried will not absorb water and can crumble or contaminate the clay with set plaster, which causes lime pops that blow out in the firing.
Correct practice: dry the bat thoroughly (it should feel chalky and light), then use it to stiffen reclaim to a workable consistency, flipping the clay so both faces dry evenly. Do not put wet reclaim on a damp bat, and do not store the bat where it stays damp. Together these changes keep the body consistent and prevent a firing defect that would only appear much later.