Natural slate tiles frequently have a cleft face, which separates into natural layers. These layers may also be present on the back of the stone, making each tile extremely uneven in thickness and size.
Due to the presence of these clefts, tile nippers, score-and-snap tile cutters and other hand-cutting tools break the tiles more frequently then cutting them in neat lines. Therefore, rather than trying to snap or break the tiles, a tile saw should be used to slice into them in a straight line.
Place a straight edge over the slate tile and draw a line with a grease pencil where you wish to make the cut. Slate's many ridges, bumps and clefts can make the cut appear to be going off its mark, so drawing a line to work from will help ensure a straight cut.
Fill the wet saw with water to keep the blade cool and place the slate tile on the table in front of the blade. Check to make sure the blade is lining up with the pencil mark on the tile.
Turn on the blade and slowly push the slate into the saw. Do not exert force when the slate comes in contact with the blade; the saw will pull it through as you apply steady pressure. Small pieces of the slate make break off as it is being cut; this is normal and will not effect the cut tile in any way.
Let the saw pull the slate all the way through the blade and turn off the saw before retrieving the tiles. Slate tiles are often covered in dried mud; the tile wet saw may produce extremely slippery tiles, so be careful removing the tiles from the table.