Wheel Throwing and Hand Building Skills
Throwing is a skill of controlled pressure, not strength. Hand building is a skill of joining. The exam tests the throwing sequence, standard faults, and the joins that survive firing.
Throwing sequence
- Wedging and checking moisture.
- Centring - both hands braced, elbows on the thighs, steady wheel speed.
- Opening - thumbs or fingers down to within 8–10 mm of the base, never through it.
- Pulling - walls 6–10 mm thick, pulled from the base up in 2–3 passes, each thinner.
- Shaping, compressing the rim, cleaning the base.
- Trimming at leather hard - turn a foot ring, refine the profile. Water is a lubricant, not an ingredient: too much water softens the clay and the pot slumps.
Hand building
Pinch for small forms; coil for large, thin-walled forms; slab for flat and angular work. Joins are made by scoring both surfaces, applying slip, pressing together and welding - never a butt joint.
Worked example: capacity
A cylinder is thrown with outside diameter 10 cm, height 12 cm, wall and base 0.8 cm. Internal diameter = 8.4 cm; internal height = 11.2 cm. Volume = π × 4.2² × 11.2 = 620 cm³. Total shrinkage 8 % linear gives a volume factor 0.92³ = 0.779, so fired capacity is about 483 mL - label it 450 mL to allow for variation.
Traps
- An S-shaped crack in the base from off-centre opening or a too-thin base.
- Thick, heavy bases that crack during drying.
- Coils joined without slip or scoring.
- Trimming too late, when the clay is stiff and chips.