Glass slumping and fusing

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Glass Slumping Process

What is the glass slumping process? Glass slumping is bending or slumping glass into or over a mold. Generally glass is slumped into ceramic molds and bent over metal molds.

To achieve this, you must take your glass through a few heating and cooling phases. There are five steps to this glass slumping process.

Read each process to see how slumping is performed in glass fusing. If you have any questions, please contact me through the contact page.

Step One – Heating Up the Glass

You will be heating the glass up to a slumping temperature. This involves placing your glass on a prepared kiln mold inside your kiln.

After turning on your kiln, you will heat the glass to anywhere from 650 degrees Celsius to about 760 degrees Celsius, depending on the look you want to achieve and your individual kiln. Allow your glass to heat up slowly to avoid thermal shock. At around 540 degrees Celsius, your glass will begin to soften and appear glossy. Once you get past this stage you should not have any problem with thermal shock.

At around 700 degrees Celsius and 760 degrees Celsius, slumping occurs. Keep an eye on your glass and make notes of your progress.

Once your glass has slumped to your satisfaction, it is time to go to Step Two.

Step Two – Soaking the Glass

In this phase, you are going to want to allow your piece to soak. Longer soaking times cause the glass to flatten out and take on the shape of the mold. You will notice that the glass takes on a smoother appearance. Now on to Step Three.

Step Three – Cooling the glass

Once your glass has slumped into your mold and you are satisfied with the look, you need to cool your glass down. Some people cool off the glass rapidly by opening the lid and allowing the temperature to drop to about 600 degrees Celsius, while others just turn off the kiln and allow the piece to cool down on its own. This is a personal preference, take notes and determine what method suits your needs.

The reason for quick cooling your glass is to avoid devitrification. Devitrification can occur at temperatures above 1300 degrees Fahrenheit. Depending on how high a temperature you have reached with your glass, you can avoid devitrification by quickly cooling your glass.

Step Four – Annealing the Glass

Once your piece has cooled to about 540-565 degrees Celsius, you begin the annealing process. This will help relieve the stress that has built up in your glass. It is important to always anneal your pieces. Soak your piece at this temperature for about 20 minutes. Then slowly drop the temperature from the annealing point.

Another method of going through the annealing stage is by slowly cooling the glass. This method allows the glass to relieve the stress as it is slowly cooled off. This is especially helpful if you are not sure where the annealing point for your particular glass is located. Cooling slowly drops the temperature through different ranges of annealing. This method is referred to as constant linear annealing or shotgun annealing.

Stage Five – Cooling Glass to Room Temperature

Once you have taken your glass through the annealing stage, and relieved the stress, it is safe to cool your piece to room temperature. There are a couple of ways to accomplish this final glass slumping process.
You can turn off the kiln and allow it to naturally cool. If your particular kiln maintains heat, the natural cooling may be adequate. This is great for small pieces of glass.

It is still important for larger pieces of glass to continue to cool down slowly. This will again help with thermal shock. The best way to avoid this problem is to continually cool and soak your piece slowly.

By following these five steps of the basic glass slumping process, you should achieve your desired results. It is always a good ideal to keep detailed records in a glass fusing log of your procedures for future reference.

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