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Bullseye Glass Co. - Recommended Annealing Cycle

Save time and energy. Anneal thick slabs at 482 degrees.

As of June 2009, Bullseye has changed its chart for annealing thick slabs. Specifically, the recommended anneal soak temperature has been lowered from 516°C to 482°C.

Why the change?

For several years we have used the new 482°C soak temperature for everything from simple fused pieces to large-scale castings, with tremendous success. We now consider it more practical than 516°C — especially on larger, thicker projects, for two reasons:

• More effective: After the stress has been relieved by holding the glass at an anneal soak temperature of 482°C, the glass cools over a shorter span of temperature in which annealing stress could be introduced than it would be if held at 516°C.

• More efficient: It takes less time to cool over a shorter span of temperature. 

What about past work that has already been made with the anneal soak at 516°C?

There is no need to worry about this work. Effective annealing has been and can be accomplished when the anneal soak is performed at 516°C. It just takes longer, especially with projects that are thicker or very large.

If your past projects have been successful using cycles with an anneal soak at 516°C, you may continue to use that temperature. Or, if you wish to save time, you can revise your cycle to have an anneal soak at 482°C. 

Why can most work be annealed successfully with either anneal soak temperature?

This is because when annealing glass, the most important factor is not the temperature at which one performs the anneal soak (within reason). Rather, the most important factor is the ability to achieve uniform temperature throughout the body of glass during the anneal soak and subsequently cool the glass in such a manner that it does not develop more than a 5°C temperature difference throughout the body of glass during the first anneal cool to 427°C. For more information on this topic, see Bullseye’s TechNotes 7: Monitoring Kiln Temperatures for Successful Annealing.

Where can the new Annealing Chart for Thick Slabs, and TechNotes 7: Monitoring Kiln Temperatures for Successful Annealing be found?

Click here to download the new annealing chart.
Click here to download TechNotes 7.

Published courtesy of Bullseye Glass Co., Revised July 2009

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