HOW TO DRILL BISQUE FOR GLASS SLUMPING MOLDS

Not all molds that make great slumping molds are pre-drilled because they were designed to be used for ceramics. You can drill holes in the molds that would be suitable for slumping. Be sure you examine the mold for crevices and areas that would keep you from removing your glass without breakage.

Holes should be drilled in bisque to allow air to release while the glass is slumping. It is recommended to use a 1/8” or 3/16” Carbide Tip Drill Bit when drilling bisque for slumping. To avoid cracking or uneven slumping it is important to drill holes in any bisque piece that you use to slump glass.

TO DRILL: Position the holes evenly on the surface of the bisque. The number of holes to drill depends on the size of the piece. Also, if the bisque piece has a foot, you may want to file the foot in several places to create an air channel to help air escape from under the glass.

So, how many holes should you drill? This chart is a guideline to help you decide:

WHICH SIDE OF DICHROIC GLASS HAS THE COATING?

It is not always easy to tell which side of clear glass has the dichroic coating. The coated side is the side that has a rougher texture.

Use any pointed object such as a pencil, toothpick or even your fingernail and hold this object to the glass. If the reflection touches the object, then this is the coated side of the dichroic glass. A space between the reflection and the object means this is not the coated side.

NEW RECOMMENDED ANNEALING CYCLE FOR BULLSEYE GLASS

New Recommended Annealing Cycle for Bullseye Glass
Save time and energy. Anneal thick slabs at 900 degrees.

As of June 2009, Bullseye has changed its chart for annealing thick slabs. Specifically, the recommended anneal soak temperature has been lowered from 960°F/516°C to 900°F/482°C.

Why the change?
For several years we have used the new 900°F/482°C soak temperature for everything from simple fused pieces to large-scale castings, with tremendous success. We now consider it more practical than 960°F/516°C—especially on larger, thicker projects—for two reasons:

1. More effective: After the stress has been relieved by holding the glass at an anneal soak temperature of 900°F/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 960°F/516°C.
2. 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 960°F/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 960°F/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 960°F/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 900°F/482°C.

Why can most works 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 10°F/5°C temperature difference throughout the body of glass during the first anneal cool to 800°F/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.