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.
Step 2 - Anneal the Glass
Heat the glass in a craft oven until it reaches 900 degrees Fahrenheit, then turn off the oven and allow the glass and oven to cool for eight hours.
This annealing or heating process will alter the glass so that it is no longer tempered and will not shatter when cut.
Step 3 - Prepare the Glass for Cutting
After the glass has been annealed, place it on a flat surface and place a t-square over the place you wish to cut it.
TIP: Dip your glass cutter into kerosene; this will allow for a cleaner cut.
Step 4 - Cut the Glass
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.
Step 6 - Smooth the Edges
Smooth the edges by running them against a whetstone. This will not only make the glass smoother and less dangerous to carry, but also strengthen the glass.
Step 7 - Re-temper Your Glass
Once you've finished cutting, you may choose to temper your glass again.