If you crack a tile you need to install or crack one you've already installed, hiding the crack can prove difficult as most tiles are patterned. Incorrectly hiding a crack in tile will show a misaligned pattern or colour gradation. With natural stone or marble tiles with natural patterns or "veins," an incorrectly hidden crack will cause the vein or striations in the stone to "jump" left or right, revealing the crack. Additionally, poor craftsmanship in repairing the tile could result in an "edge" that you can feel. The trick to hiding cracks consists of creating the illusion that veins or striations remain unbroken.
Glue the edges of each piece of the cracked tile with the super glue.
Lay the edges on a flat surface.
Align the broken pieces of the tile as best as you can. Sometimes, the crack will vanish when you align both pieces together. Make sure you feel the tile surface with your finger and adjust the alignment until you achieve a near-flat surface.
Rubber band the pieces together for 10 to 12 hours until the glue dries.
Power grind the spare tile, catching the stone dust in the metal bucket.
Mix one thimble full of ceramic tile dust with a pinch of grout.
Squish the filler into larger cracks that the glue wouldn't hide.
Flatten the filler with your finger tip.
Scrape excess filler away with a one-sided razor blade. Continue adding filler and scrape it away until you achieve a smooth surface you can barely feel.
Apply polyurethane to match surrounding finish using the paintbrush.
For tiles you crack while cutting or shaping, always try to align the crack because this will often make it disappear altogether. For pre-installed tiles that somehow got cracked, fill with pulverised powder and grout. If you don't want to power grind the tile, you can crack a section off using a ball peen hammer. Crush the fragments into a fine powder before mixing with the grout.
Don't use plain grout to hide cracks because it will never match perfectly. Using pulverised stone or tile mixed with matching grout improves your chances of obtaining an imperceptible repair job.