I have started using more underglaze on a red clay body. Jason Burnett posted his soda ash wash recipe for unglazed surfaces. This wash will allow the matte underglaze to have a moist, saturated look. Apply two coats of wash allowing to dry between coats. You can apply wax resist so that glaze does not get on this area.
Soda Ash Wash for non glazed surface:( fires cone 06-cone2)
57 grams of soda ash
1 cup heated water
Stir to dissolve