Wedging and Forming Methods
Wedging removes air and evens out moisture before forming; each forming method has a characteristic defect. The exam tests which method suits which product and how to avoid the classic faults.
Wedging
- Spiral (kneading) wedging - for 1–5 kg batches; pushes air out in a spiral, so never re-fold along the same axis.
- Wire / cut-and-slam wedging - for large batches; cut, slam, repeat 20–30 times.
- Vacuum pugging - replaces hand wedging in production. Purpose: homogenise, remove air pockets, equalise moisture, align particles so the clay throws evenly.
Forming methods and their niche
- Pinch, coil, slab - hand building; one-offs, large forms, slabs for tiles.
- Wheel throwing - round, hollow, symmetrical ware.
- Slip casting - hollow, complex or non-round shapes in quantity.
- Jiggering / jolleying - plates and cups, profile formed against a rotating plaster mould.
- Extrusion, pressing, RAM pressing - tiles, handles, sanitaryware.
Worked example
A 20 cm coil-built cylinder is to be built in three stages. Coils of 1.5–2 cm diameter, rolled evenly, are joined with a cross-hatched joint and slip, then welded on both faces. Each stage is covered and dried to leather hard before the next, because joining onto a dry body gives a weak, cracking seam.
Traps
- Wedging clay that is too wet - you smear it instead of homogenising it.
- Making coils from a different body or moisture content to the base.
- Joining slabs with butt joints and no slip.
- Over-working plastic clay until it becomes short and unworkable.