When working with ceramic tile, sooner or later you will need to cut one. When you do, you'll be left with a raw cut edge. The most common way to seal that cut edge, at least for cosmetic reasons, is to set the tile with mastic or mortar and then apply grout around it. The cut edge of the tile along with the other three edges will be sealed in grout. But if you aren't intending to grout and you need that cut edge to be sealed there's a simple way to do it.
Smooth the cut edge of the tile with a tile smoothing stone--a man-made stone made up of grit that can sand a cut tile edge and make it smooth.
Wipe the dust from the edge of the tile with a clean dry cloth. The unglazed portion of the tile must be free of dirt, grease and wax.
Dip a brush into liquid penetrating sealer such as Glaze N Seal and paint it on the edge of the tile. If any of the sealer drips or flows onto the glazed surface of the tile wipe it away immediately.
Any sealer that is not absorbed into the unglazed portion of the tile after two minutes should be wiped off.