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What it does:
Changes the glass to the desired state.
Things to consider:
When fired correctly, this is the only stage of firing that makes permanent, visible changes your glass . The schedules for firing glass of a given thickness to a tack fuse, soft (dimensional) fuse, and full fuse will all be identical except for this step.
During this critical phase, the best way to achieve the desired results is to look in the kiln and observe the changes as they happen. At process temperature, the glass is well past the point of thermal shock so the only risk of looking into the kiln now is personal safety. Ensure you are wearing proper, high-temperature gloves, eye protection (#2 welding glass work well), and natural fiber clothing (your skin preferrs singed clothing over melted clothing).
When looking into a kiln at process temperature, here are some things that will help you understand what you are seeing:
- At fusing temperatures, all glass glows red. While different colors may appear as different shades of red, it is not uncommon to visually “lose” your design at this point. As the glass cools, the colors will return.
- The bright glow of the elements and the wet-looking molten surface of the glass make it difficult to see the shape of the surface. One way to judge the flatness of the glass is to look for the reflection of the lid elements. When the glass surface is not flat, the reflection of the elements will be distorted as if viewed in a fun house mirror.
While process temperature is important, process time is equally critical to your results. You may find, for example, that holding 1475° F for 5 minutes and holding at 1425° F for 15 minutes both give you the same result. When in doubt, always choose lower, slower, and longer. Why? Glass melts more predictably when it heats evenly.