Tempered glass, or toughened glass, is a form of safety glass that is specially treated to ensure that should it ever break, it will shatter into tiny crystals as opposed to breaking into large, sharp, and dangerous shards.
Because the glass is specially engineered to distribute pressure and break in a specific way, deliberately cutting tempered glass can be tricky.
There is a special process that you must follow when attempting to cut toughened glass, otherwise it will shatter and no longer be usable. It is important to use extreme caution as you go through the process so that you do not get injured.
Step 1 - Clean the Tempered Glass Thoroughly
Make sure there is no dust or dirt particles that could get in the way of a clean cut. Clean it thoroughly with window washing solution and allow it to dry completely.
While pressing down with moderate pressure, run the cutter along the straight edge in one smooth motion to make a thin line across the top of the glass. Do not run the cutter over the glass again.
Step 5 - Separating Your Cuts
Place the dowel under the line and position your hands on either side of the glass. Press downward on both sides of the dowel. If you've done everything correctly up to this point, your pressing should snap the glass evenly down the line.
WARNING: This is one of the most sensitive and dangerous parts of the process. Be sure you are wearing protective gear before you proceed.