Annealing Bullseye
Annealing, the controlled
cooling of a glass, is critical to its longevity. Glasses which are not properly
annealed will contain stress which may result in breakage before or at any
time subsequent to their removal from the kiln.
The following chart represents a simple schedule used routinely in Bullseye's
factory studio. Annealing schedules for thicker pieces (up to 8") are available
from the factory upon request.
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ANNEALING
A TYPICAL (12" DIAMETER) BULLSEYE GLASS PROJECT
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| Thickness (inches) | Anneal
Soak @ 960 ° F (In Minutes) |
Anneal Cooling Rate 960-750° F (°F/HR) | Actual Time In Range 960-750 ° F | Cooling Rate* 750 ° F To Room Temp (°F/HR) | Actual Time* In Range (750°F To Room Temp) |
| 1/8" | 15 min | 420 | 30 min | 1013 | 40 min |
| 3/16" | 23 min | 280 | 45 min | 675 | 60 min |
| 1/4" | 30 min | 210 | 60 min | 500 | 80 min |
| 3/8" | 45 min | 140 | 90 min | 335 | 120 min |
*Most kilns will not cool this rapidly due to residual heat in the refractories. Allowing the kiln to cool at its own rate between 750 ° F and room temperature is usually adequate for the final cooling stage. This may result in an actual cooling rate slower than that shown above. Cooling the work by opening the kiln door or large vent hole, however, risks thermal shock.