Flocculant is a chemical product for producing flocculation of suspended particles, as to improve the plasticity of clay for ceramic purposes.

The addition of Epsom salts is commonly done with engobes. A gelled engobe will apply in an even coat and stay in place even though it takes time to dry. Without the Epsom salt addition, it will run and drip (even with low water content). It is better to add Epsom salts as a saturated solution (rather than in powdered form) since the system is so sensitive to over-gelling if too much is added.

It can thicken a glaze to improve adhesion to non-porous surfaces. Also acts as a suspension agent in slips or glazes. Adding too much can have an adverse effect.

References: Creating Saturated Epsom Salt (Flocculant) Solution