Rough cut or nipped ceramic tiles will almost always have sharp edges to deal. In particular, nipped edges will not only be sharp but serrated as well and, for any practical purpose, they need to be smoothed over--if not for safety's sake then for the aesthetic appearance. Whenever you are sanding or nipping ceramic tile, it is important to take precautions to protect your eyes.
Manually Sanding
The rougher the edge on the ceramic tile, the lower the grit of sandpaper needed to smooth it out. Use 60 or 80 grit for starters, just to dull the edge or flatten the serrations if the tile has been nipped. Once the edge has been dulled, work your way up to 200-grit sandpaper and then 400-grit sandpaper to polish the edge for maximum smoothness.
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Power Sanding
You can also get good results with a rotary sander for curves and a belt sander for flat edges. Power sanding also begins with a lower-grit sandpaper, but you must use caution since using power will sand off much more tile faster than doing it by hand. Apply gentle pressure when using power, checking the edge after each pass. When the sharpened edge has been removed, begin to polish it with 200-grit and then 400-grit paper, either using power or manually polishing it with your hands.
Filing Down the Edge
Many types of files are made to sand down ceramic tile edges. Because they are already mounted on a handle, they give much better control than using a power sander. Files are perfect for sanding curved edges and can be found in a variety of grits or coarseness.
Alternative Methods
In a pinch, any concrete slab or cement block can be used to sand down the rough edge of a ceramic tile. You will need to hold the tile itself and slide it back and forth across the slab or block. This will only work for straight edges. However, it is an effective way to remove the sharp and potentially dangerous edge from any ceramic tile.