There are a number of different methods of cutting tiles for installation. Some of the more common methods involve scoring and snapping or using a pair of nippers with a carbide tipped pencil. And while these methods are suitable for installing ceramic tile, or even some types of glass tile, they are inadequate when working with stone.
Stone tiles, and to some degree high density porcelain tiles, cannot be scored and snapped in the same way that a more brittle ceramic tile can be. Most stones are too hard and dense to be able to snap along the line without extreme amounts of pressure. The few stones that may be able to snap without that amount of pressure may not fracture cleanly. Slate tiles, for example, may fracture along many different layers, resulting in a jagged cut rather than a clean one.
Similarly, standard nippers do not have the jaw strength to cut through stone mosaics without crushing them in the event of a more brittle or fragile stone.
When cutting stone tiles, a wet saw with a diamond encrusted blade will always give the best cuts. A wet saw cuts the stone without any pressure, removing a small amount of the stone while the water keeps the blade cool enough to avoid overheating due to friction. The edges of stones cut this way can be tightly fit together, because the edges are tightly defined. In the same way, if the stone needs to be drilled, a diamond tipped drill bit dipped in cooling oil can quickly grind through the stone to make the necessary hole without smoking, overheating, or breaking the stone.
Stone mosaics can be cut in sheets on a wet saw as well, but if individual stones need to be cut, stone nippers should be used. Stone nippers have a large enough jaw to be able to snap the mosaics cleanly without crushing them.
Using the right tools will help ensure a good stone installation every time. Always use tools designed for cutting stone to get the best results.