Tempered glass is a special type of glass to protect something. Because of this, it cannot be cut in the same way as ordinary glass. If you want to cut it, you'll need to heat it to near 538 °C, then cool it slowly. This process, known as annealing, is very effective at reversing the strengthening process of glass and making it weak so that it can be cut. Once cool, the protective glass is ready to be cut. Use the annealing process if you have a glass kiln. If not, you'll need to take it to a glass cutter expert. If you have to cut glass that is more than 25 cm in diameter, it's best to take it to a professional.
Step
Method 1 of 2: Annealing the Protective Glass
Step 1. Find a furnace that can be used to process glass
The intense heat in the furnace is needed to soften the glass layer and start the annealing process. This furnace is usually in the art classroom. You may be able to gain access to this furnace through an arts education program at the nearest college.
- The annealing process will distribute heat evenly to the protective glass so that the pressure point of the strengthening process will be lost. The presence of pressure points is what causes this object to break into small pieces when cut.
- Without the presence of these pressure points, the protective glass can be cut without breaking it.
Step 2. Place the protective glass over the heat-resistant container, then add the water
Add enough warm water to cover the entire glass. If the glass is not too thick, 1.9 cm of water should suffice.
- If you don't have a heat-resistant flat case, ask the art studio manager if you can borrow one. If you're not in an art studio, talk to the caretaker or owner of the stove you're using.
- You can also buy these containers at art supply stores or glass stores.
Step 3. Heat the protective glass immersed in water with a furnace for 30 minutes
The glass must reach a high enough temperature for it to lose its strength. So, turn on the furnace until the temperature reaches a minimum of 468 °C and heat the glass to a temperature sufficient to start the annealing process. Heating time varies based on the size of the glass being heated, but most glass takes about 30 minutes in the furnace. When finished, the glass will reach an even temperature throughout.
- Heat the Effetre (Moretti), Bullseye, and Lauscha type glass at 504 °C. Heat the Borosilicate glass to 566 °C. Satake protective glass should be heated to 477 °C. Use the built-in temperature control in the furnace to keep the temperature stable.
- Heat a sheet of glass measuring less than 2.5 cm for 20 minutes. This will weaken the object making it easier to cut. If you want to annealize larger glass, heat the glass while soaking it for 8 hours.
- If you are using an annealing process to weaken a large paperweight, soak and heat the object for 12 hours. Very large pieces of glass weighing more than 45 kg can take months to process.
Step 4. Cool the glass slowly until the temperature is below the tensile point
If you do not know the type of glass you are working with, lower the furnace temperature to 427 °C. The temperature of 399 °C is suitable for cooling Satake glass. Cool the protective glass in the furnace for 2-3 hours.
- Lowering the temperature of the glass too quickly can put additional stress on it, making the processed glass weaker.
- The strain point is the temperature point at which the pressure inside the glass sheet decreases. Once the temperature drops below that point, the glass is stable and doesn't shatter.
Step 5. Remove the glass from the furnace after it cools down
After the glass has “cooled” for 2-3 hours, remove it from the stove. This thing is still very hot. So, use special tongs to remove it from the furnace. To be safe, wear thick gloves when opening the stove and handling tongs. Place the glass on the cooling rack. Let the glass sit overnight before cutting. Cutting glass while it is still hot can cause serious injury.
When processed glass is cooled in a furnace, the outside will cool faster than the inside. Just because the outside feels cold, doesn't mean the inside is ready. Cooling the glass slowly can prevent pressure build-up making it easier to cut
Method 2 of 2: Cutting Glass That Has Been Annealed
Step 1. Clean the treated glass surface with a window cleaning product
Spray the glass 4-5 times with cleaning liquid. Wipe dry with a clean, dust-free cotton cloth. Cleaning the glass can ensure the cut is smooth and accurate.
You can buy window cleaner at a home supply store or supermarket
Step 2. Wear protective eyewear and leather gloves to protect yourself
After the annealing process is complete, the glass can no longer be called a protective glass. When broken, the object will turn into sharp pieces of glass that are dangerous. Protective glasses are used to protect the eyes from sharp shards of glass.
If you don't have protective eyewear or gloves, buy them at your nearest hardware store
Step 3. Mark the part to be cut with the straight edge tool
An iron ruler can also be used for this. Measure precisely the part to be cut, then place the straight edge across. After that, use a permanent marker to draw a straight line in that section.
You can buy straight edge at a hardware store
Step 4. Scratch the surface of the glass with a glass cutting tool
Hold the straight edge in place as you scratch the surface of the glass to make marks. Press the glass cutting tool into the glass surface, starting at one end, then pulling to the other marked end. Apply moderate pressure all over the area to be cut so that there are clear scratches.
- Purchase glass cutting tools at your nearest hardware or home supply store.
- Do not scratch the marked area on the glass surface more than once.
Step 5. Place a 0.64 cm diameter wooden stick under the stroke you just made
Align the stick until it is completely parallel to the stroke. Otherwise, the glass may shatter when pressed. Do not use a large diameter wooden stick as this may cause the glass to not be cut accurately.
You can buy these sticks at your nearest hardware or home supply store
Step 6. Apply sharp, rapid pressure on both ends of the stick
Press using both your hands at the same time. Make sure the pressure on both sides is the same. The glass will be neatly cut in half.
- Don't place your hand on the stick just as you press it. Otherwise, your hands could be injured by the broken glass rim.
- For safety reasons, wear leather gloves and protective eyewear during this process.
Step 7. Smooth the edges of the freshly cut glass
Use 10 grit sandpaper to smooth the rough edges of the glass. This will make the glass stronger and safer to touch and use.
- If you skip this step, the rough parts of the glass may injure your hands.
- To prevent shards of glass from getting into your eyes, wear protective goggles during this process.
Tips
- Protective glass, under normal conditions, cannot be cut. If you try to cut the protective glass in the same way as regular glass, the surface will break into small pieces. This is because the protective glass has gone through a series of special processes that make it stiff, tough, and uncut.
- If you want to cut protective glass but can't find a usable furnace, take the glass to a professional glass cutter. An expert may be able to cut the protective glass with a laser.
Warning
- Be careful when using furnaces and working hot glass. Touching the inside of the furnace or hot glass surfaces can cause serious, painful burns.
- If you work in a crowded art class, remind other students not to touch hot glass until it has cooled overnight.
