Cut curved panels of cardboard and tape them around the sides of the tub to form a rounded cauldron shape. Ensure all gaps are tightly taped.
Wrap black trash bags over the cardboard form and secure with tape. This creates a smooth outer layer.
Dip newspaper strips into the paste and layer over the surface. Let it dry completely to add durability.
Apply spray foam insulation along the rim to mimic overflowing potion. Let it expand and harden for a few hours.
Once dry, spray the entire cauldron with black paint. Add shading around the foam for a melted, scorched look.
Dry brush purple, green, and yellow paint over the foam for a glowing, enchanted effect.
