How to Cut Tempered Glas
The process of how to cut tempered glass cannot be accomplished. Tempered glass is essentially a safety glass, and if you attempt to cut it, you will end up shattering the tempered glass into many tiny pieces. While you cannot learn how to cut tempered glass, you can learn how to anneal tempered glass so that it can be cut and re-tempered.
Understand the annealing process. This process will uniformly heat up the tempered glass so that all the stresses from the tempering process will be removed. These stress points are the reason that no one can cut tempered glass.
Begin the annealing process. Soak the tempered glass at a steady, warm to hot temperature until it reaches the annealing temperature of η = 1013 Poise in a kiln. The soaking time will vary based on the size of the glass you are annealing.
Effetre (Moretti), Bullseye, and Lauscha glasses should be soaked around 940 degrees Fahrenheit (504 degrees Celsius). Borosilicate glass should be at 1,050 degrees Fahrenheit (566 degrees Celsius). Satake tempered glass is best at 890 degrees Fahrenheit (477 degrees Celsius). Small beads require only about 20 minutes of soaking, large beads require 1 hour, and large paperweights can take 12 hours. Very large pieces of glass weighing 100 pounds (45 kg) or more can take months to anneal.
Put your 1/4-inch (0.6 cm) wooden dowel directly under the line you just cut, and apply sharp, sudden pressure on both sides of the dowel. The glass will now snap at the line into 2 cleanly cut pieces.
Sand the edge of the freshly cut glass with a whetstone. This will make the glass stronger and safer to handle and touch.
Re-temper the glass, if desired. Re-tempering glass is best left to professionals because it is a complex chemical process.
Cool down the glass slowly to where it is below the strain point temperature (η = 1014.5 Poise). This must be done slowly enough so that additional stress does not develop. A cooling temperature of 750 degrees Fahrenheit (399 degrees Celsius) for Satake glass and 800 degrees Fahrenheit (427 degrees Celsius) for every thing else works well. Cool in the kiln until the glass is at room temperature.
Prepare and cut the annealed glass after you put on your safety goggles. Use a straight edge to make your cut line, and keep the straight edge in place along the line. Use your glass cutter to cut along the line, and use medium pressure throughout the entire line to create a scratch. Do not run the glass cutter along the line more than 1 time.
