A separate primer is generally not recommended under Savella clay paint. Clay adheres best to a porous surface, and a primer can reduce the absorbency of the substrate. This may weaken adhesion and the durability of the paint surface, and more layers may be required to achieve an opaque finish.
If it is necessary to even out the color or absorbency of the base, choose a treatment according to the surface. For example, lining paper, a thin coat of clay plaster, or a priming layer made with Savella's clay shade can be suitable for this.