Most stains do not develop their color well without a glassy phase and others insist on being mixed with a ceramic medium having a sympathetic chemistry. For example, chrome-tin pinks will not develop well in zinc bearing mixes or those lacking sufficient calcium. Slips have a characteristic firing shrinkage. This must be compatible with the body so that during the firing they shrink together and the slip-body bond is not weakened or compromised. Slips have fired adherence properties that make them either loosely or tightly bonded to the underlying body.
Slips have their own coefficient of thermal expansion and act independently of the body.
If sufficient incompatibility exists, sudden heating or cooling will overcome the slip-body bond and the slip will flake or shrink off. If a glaze is applied over a slip, the slip acts as a buffer layer and it must be expansion compatible with both the underlying body and the overlying glaze. Individual slips have a characteristic dry hardness. Slips develop characteristic fired surface qualities. They can be smooth, silky, glassy, textured, dry, stippled, etc.