A Cracking Clay Bust Before the Kiln Booking
A 28 cm clay portrait bust was modelled over a crumpled newspaper core taped to a wooden board, with a 4 mm aluminium armature wire running from the board through the neck. It was left on a bench beside an open window on Friday. On Monday the neck has a 6 cm crack, the left shoulder has lifted, and the surface is leather-hard. The kiln is booked for Thursday; the work must be bisque-fired for the school exhibition. The clay is a local red earthenware with grog. The student wants to fill the cracks with fresh clay and load the piece as it is. The workshop has no pug mill, but has slip, a fork, a spray bottle, plastic sheeting, and a heat gun. Advise the student on diagnosis, repair, hollowing, and firing, and say what must be removed before the work goes near the kiln.
1. Diagnose the crack and the lifted shoulder. Consider drying shrinkage, the newspaper core, the armature, and the open window.
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The open window created a draught, so the surface dried and shrank before the interior; the solid clay mass could not accommodate that differential, and the stress concentrated at the neck, the thinnest junction. The newspaper core is compressible and absorbs water; as it dries it shrinks and can pull away, so the shoulder lifted where the clay was thin over the core. The 4 mm aluminium wire and the board also restrain shrinkage, adding stress at the neck. This is not one fault but three: uneven drying, a compressible core, and a rigid armature. Filling the crack with fresh clay alone would fail because leather-hard clay has already shrunk; new clay will shrink again and crack at the joint unless the area is rehydrated, scored, and slipped, and even then the repair is weak.
2. Give a 48-hour plan for hollowing, repair, drying, and firing, and state what must be removed before the kiln.
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First wrap the bust in plastic with a damp cloth for 12-24 hours to equalise moisture; do not add water directly. Turn it upside down, cut a 10-12 cm opening in the base, and remove all newspaper, tape, and the aluminium wire. Scrape the interior to an even 1-1.5 cm wall, keeping the neck and shoulders no thicker than the rest. Re-seat the base with scored edges and slip, and support the shoulder with a padded prop. Repair the crack by V-grooving it, dampening, scoring, and pressing in slip-soaked clay; wrap the neck with a plastic strip to slow drying. Dry under a loose plastic tent with a few holes for 5-7 days, away from the window and heat gun. Before firing, confirm there is no wire, no newspaper, and no thick solid section. Aluminium melts well below bisque temperature and leaves a void and staining; trapped paper turns to steam and can explode the piece. If the work is not dry by Thursday, do not fire it; a failed firing destroys the work and can damage the kiln.
3. What would you do if the clay is already too stiff to hollow without breaking?
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I would not force it. I would wrap the whole piece in a damp towel and then plastic for 24-48 hours, checking every few hours, until the neck and shoulder are leather-hard again rather than bone-dry. If it is already bone-dry, rehydration will cause uneven swelling and likely new cracks; in that case the safer decision is to keep it as an unfired study or remake the bust with a proper hollow armature. For the exhibition, a well-made unfired work with a written note is better than a fired piece that explodes. The judgement is to protect the kiln and the other students' work, not to rescue one piece at any cost.