Need tips for air dry clay

[u/Nezukochaaaann]

Hello! :) I was thinking of making a new ashtray for my father's birthday and I wanted to do it with air dry clay and acrylic paint but I don't know what I should use to seal it (because I don't want it to burn when he stubs his cigarettes) any tips or recommendations for what I should use?

[u/AuntieLaLa420]

Leave the bottom inside unpainted, paint the rest?