Squeeze out a two-part epoxy glue onto a scrap piece of cardboard and mix the glue according to the package instructions. Use a toothpick to put the glue in the crack, filling it all the way to the top level of the tile.
Wipe off excess glue with a clean rag. Let the glue dry according to the package directions.
Paint over the crack with a small artist's brush. Use an interior paint that matches the tile color. Let the paint dry 24 hours.
Apply a thin layer of clear urethane over the paint, using the artist's brush. Let the urethane dry for 24 hours.