Reclaiming clay is the process of turning scraps, trimmings, and dried-out clay back into workable material rather than discarding it. Trimming curls, a piece that cracked before firing, and clay left out too long and gone hard are all routinely reclaimed rather than thrown away, since dry, unfired clay can be rehydrated and reused indefinitely, unlike a piece that has already been fired.
Dry clay scraps are broken into smaller pieces and slaked: submerged in water in a bucket or tub until the water fully saturates the clay and it breaks down into a soft, saturated mass, typically over a day or more depending on how dry and how large the pieces were. Once slaked, the excess water is poured or scooped off and the resulting soft clay is spread out on a plaster bat or other absorbent, non-stick surface to stiffen back up to a workable consistency, since slaked clay is initially far too wet and sticky to use directly. Once it reaches a workable stiffness, it is wedged (kneaded to an even consistency and to work out trapped air) the same way any fresh clay is before use.
Reclaimed clay needs to be kept separate by body type; mixing two different clay bodies together in the reclaim bucket produces a blended body with its own, generally unpredictable, firing behavior, which is why studios that use more than one clay body typically keep a separate labeled reclaim bin for each. Trimmings and scraps that are still damp can usually be added straight to a reclaim bucket without a separate slaking step, while fully dry, bone-hard clay needs the full slaking process to break back down. Reclaiming reduces both material cost and the amount of clay sent to landfill, part of the broader material-waste picture covered in environmental impact.
Plaster contamination is a real risk worth guarding against, distinct from the ordinary, safe use of a plaster bat to stiffen reclaimed clay: a stray flake or crumb of plaster, from a chipped or deteriorating bat or from plaster mold scraps mixed in by mistake, can end up buried inside a reclaimed batch. Buried plaster absorbs moisture and expands during firing, which can pop a small crater out of the fired surface or crack the piece outright, a defect commonly called lime-popping. A reclaim bucket kept away from plaster mold-making scraps, and bats replaced once their surface starts to crumble rather than staying smooth, avoids introducing the problem in the first place.