Cone 04 is higher than cone 06 but ware is still very porous and weak. While it might be able to withstand handling, it may not be able to withstand being burst by its own glaze. Or shivering. Or crazing. Consider using a terra cotta with an white engobe. Fire to cone 03. This piece has a black engobe on the outside and a glaze under compression on the inside.
Potters know artware as pottery firing at low temperatures with brightly coloured glazes and decorated using decals, underglazes, lustres, etc.