Understanding Firing Schedules
Home › Forums › Glass Fusing › General Fusing Discussion › Firing schedules for smaller pieces? › Understanding Firing Schedules
September 7, 2008 at 4:24 am #10723
Rather than give you a schedule that will work in one specific situation, here’s some help taking any schedule and adapting it for your needs at the time.
Most firing schedules have 6 major parts – some can be accelerated for small glass – others cannot.
- Initial heating: From room temperature to the point at which the glass starts to soften and can no longer thermal shock. Thermal shock is caused by uneven heating of the glass. With small glass uneven heating is less likely so this part of the schedule can usually shortened. If you get past about 1000°F and the glass didn’t break then you’re good.
- Final heating: From the end of the initial heating to the process temperature. This part of the schedule is already pretty fast so there isn’t much opportunity here.
- Process temperature: Where the fuse, slump — or whatever the goal is — occurs. This usually doesn’t change for different sizes of glass.
- Initial (rapid) cooling: Cool the kiln and glass to the annealing range. This part of the schedule already has the kiln cooling as fast as it can so no opportunity to speed it up here.
- Annealing: Cool the glass slowly enough to to minimize internal stress as the glass transitions to a solid. The length of this segment is determined primarily by the thickness — regardless of size.
- Final Cooling to room temperature. As with the first part, the only goal here is to not thermal shock the glass. If you anneal properly and get to room temperature without breaking the glass then you’re successful.
So, the short answer is, for small pieces you can accelerate the initial heating and the final cooling significantly. The actual speed will depend on the work, the kiln and your appetite for risk
Helios Kiln Glass Studio