# Bisque Firing Schedules

Unit: The First Bake: Bisque Firing
Topic: Bisque Firing Schedule
URL: https://claybook.studio/learn/bisque-firing-schedules/

# How the Kiln Climbs to Temperature

After candling, the kiln begins its main climb to bisque temperature. Understanding what happens at each temperature range helps you fire confidently and troubleshoot problems.

## Key Temperature Events

**100–200°C (212–390°F): Mechanical Water Out**
Any remaining free water evaporates. This is what candling handles. If you skipped candling, this is the danger zone for explosions.

**350–600°C (660–1110°F): Organic Burnout**
Organic matter in the clay (plant material, carbon from organic additives) burns away. The kiln needs ventilation here. Keep the lid propped or a bung hole open to let gases escape.

**573°C (1063°F): Quartz Inversion**
Silica in the clay undergoes a rapid crystal structure change. This causes a small but sudden change in volume. Both heating through and cooling through this point must be done slowly to avoid "dunting" (sudden cracks from thermal shock).

**600–1000°C (1110–1830°F): Bisque Range**
The clay begins to sinter: particles bond together permanently. The pot is no longer soluble in water. Most bisque firings end between cone 022 (600°C) and cone 06 (999°C).

## A Simple Bisque Schedule

*   **Candling**: 80°C for 2 hours.
*   **Slow climb**: 80–600°C over 3 hours (approx. 170°C/hour).
*   **Medium climb**: 600–1000°C over 2 hours (approx. 200°C/hour).
*   **Hold at peak**: 15–30 minutes at final temperature.
*   **Cool**: Let the kiln cool naturally. Do not open until below 100°C.

## Schedule Verification Checklist
Before pressing start:
* Confirm vent strategy for burnout range
* Confirm cone placement visibility
* Confirm cooling plan includes safe opening threshold

A clear schedule prevents rushed decisions mid-firing.

## Did You Know?

The critical moment at 573°C is known as [quartz inversion](https://en.wikipedia.org/wiki/Quartz_inversion), a rapid crystal structure change in silica that can crack pots if the kiln passes through it too quickly. Potters track these temperature events using [pyrometric cones](https://en.wikipedia.org/wiki/Pyrometric_cone), small ceramic pyramids calibrated to bend at specific heat-work levels, providing a visual record of what happened inside the kiln.

## Check your understanding

### Question 1: Why must the kiln be well ventilated between 350–600°C during bisque firing?

- [ ] A. To cool the kiln elements
- [x] B. Organic matter burns and releases gases that must escape
- [ ] C. To allow new air into the kiln
- [ ] D. Ventilation is not needed below 1000°C

Tip: Organic matter in the clay burns away in this range, releasing gases that need to escape. Trapping them can cause discolouration or bloating.

### Question 2: What is "quartz inversion" and why does it matter for firing schedules?

- [ ] A. The point where clay turns to ceramic permanently
- [x] B. A rapid silica crystal change at 573°C that can crack pots if passed too fast
- [ ] C. When the kiln elements reach maximum output
- [ ] D. The reversal of heat direction inside the kiln

Tip: At 573°C silica rapidly changes crystal structure, causing a small volume change. Passing through too quickly causes dunting: thermal shock cracks.