Use a glass scoring tool to make straight lines. If you plan to make longer, straight cuts on tile 1⁄8 inch (3.2 mm) thick or less, use a glass scoring tool. Scoring refers to cutting small cuts in the surface of the glass that will allow you to break the piece off with a clean edge.. Choose a scoring tool with a carbide or diamond cutting wheel to score the glass.
Scoring and snapping allows you to cut larger squares of tile into smaller squares and isn’t ideal for cutting irregular shapes or patterns. The cuts need to be at least an 1 inch (2.5 cm) wide in order for you to snap it off, so scoring is not a good method to cut thin slivers of glass tile. You can find glass scoring tools at hardware stores or online for about $15.
Lay the glass tile face up on a flat surface. When you score and snap, you want to make your cuts on the front facing side of the tile so the visible part of the tile has the straightest line. Place the glass tile on a workstation or table with the side that will be facing out when you install the tile facing up.
Be sure to lay the glass tile down gently to avoid chipping or cracking it. Tip: Consider laying a towel or cardboard down beneath the glass tile to keep it from knocking against the surface.
Use a straightedge and washable marker to draw guidelines. Scoring and snapping is ideal for breaking glass tiles across their entire surface, rather than cutting sections out of a larger piece of glass tile. To give yourself a guideline, place a straightedge on the tile, and use it to guide your washable marker as you make a straight line across the tile. Washable marker will wipe off easily after you snap off your glass tile.