Scoring is scratching criss-cross lines into two clay surfaces before joining them with slip, so the clay knits together. Score and slip is the standard way to attach handles, coils, slabs and other parts.
What Is Scoring?
Clay surfaces that are simply pressed together tend to separate as they dry, because there is nothing locking them. Roughening both faces with a needle tool, fork, serrated rib or scoring tool, then brushing on slip, gives the clay particles a way to interlock when you press the pieces together.
The parts need to be at a similar dryness, ideally leather hard, so they shrink at the same rate afterwards. Joining a soft handle to a firm mug is a common cause of cracks at the join, even if it was scored well.
After pressing the joint together, blend the seam with a finger or tool, and add a small coil of clay into inside corners for strength. Covering the piece loosely with plastic for a day or two slows the drying of the join.
Some potters use magic water, a mix of water with a little sodium silicate, or vinegar instead of slip. Whatever you use, consistent scoring and slow drying are what make joins reliable.
This pottery glossary entry from Le Studio Art Space is general educational content. Always follow the clay, glaze and kiln makers’ data for your own materials and equipment.