Sealing porous clay tile with stamped design.

[Chipilink]

I stamped my design porous unglazed clay tiles using a rubber stamp and indelible black ink. The design when dry smears with a black smudge when wiped with a paper towel. I'm thinking that the tiles need to be sealed somehow. I don't want to use any kind of varnish. I'd rather reapply sealer from time to time. I have also considered some sort of encaustic (hot wax) treatment. Please help. Thank you!