lemon juice will leave a mild etch mark. On a ceramic tile you should have no effect whatsoever.

Its a little tricky when you first start out. That's why I like the scratch test. Go to a closet or a deep dark corner of the room.. Scratch (a little bitty scratch mind you). If its ceramic tile, your razor will just slide along the face of the tile. if its stone (limestone mainly), your blade will actually be able to scratch the stone. A little bitty scratch is all u need to let you know it aint ceramic tile.