Ceramic clay remains fragile after drying: its durable transformation requires a pottery kiln operating within that body's firing range. A kitchen oven cannot produce that transformation. Air-dry clay hardens without ceramic firing and can suit indoor ornaments, but varnish does not turn it into dinnerware or a water container. Polymer clay is another material: it requires the curing process on its package, usually a controlled household oven; simply waiting does not harden it.
Before buying, decide between a decorative object and pottery that will be fired. Without studio access, air-dry material lets you explore shaping; follow its own thickness, water and finishing instructions. For a ceramic bowl, first establish where it will be fired and which bodies the studio accepts. Do not mix unidentified materials or send polymer or air-dry clay for ceramic firing. Keep the product name, manufacturer and code: wet colour does not identify composition.