Firing a kiln is more than just turning it on and waiting. Understanding bisque vs glaze firing, how to set a firing schedule, when to use holds, and how cooling affects your work makes the difference between consistent results and unpredictable ones. This guide covers everything you need to know about firing an electric kiln.
Bisque Firing vs Glaze Firing
Most pottery goes through the kiln twice — once for bisque and once for glaze firing.
Bisque Firing
Bisque firing converts raw, bone-dry clay into a hard, porous ceramic that can hold glaze. The standard bisque temperature is cone 04 (approximately 1945°F / 1063°C) for most clay bodies, regardless of what cone they’ll be glaze fired to later. Bisqueware is still porous enough to absorb glaze, but hard enough to handle without breaking.
Bisque firings are more forgiving than glaze firings — you can fire pieces closer together, stack lightly if needed, and fire more slowly without major consequences. The most important thing is to fire slowly in the early stages to allow remaining moisture and organic material to burn out of the clay.
Glaze Firing
Glaze firing melts the glaze onto the clay surface and vitrifies the clay body. Glaze firings require more precision — pieces must not touch each other, glaze must be kept off kiln shelves, and the firing schedule needs to match your clay and glaze system. The temperature depends on your clay and glaze cone — typically cone 6 for mid-fire or cone 10 for high-fire.
Firing Schedules: Ramp and Hold
A firing schedule is a programmed series of temperature ramps (how fast the temperature rises) and holds (how long the kiln stays at a set temperature). Modern digital controllers let you program these precisely. Here’s a typical cone 6 glaze firing schedule:
Segment
Rate (°F/hr)
Target Temp
Hold
Purpose
1
80°F/hr
250°F (120°C)
30 min
Drive off remaining moisture
2
200°F/hr
1000°F (538°C)
None
Burn out organics
3
150°F/hr
1700°F (927°C)
None
Approach quartz inversion carefully
4
108°F/hr
2232°F (1222°C)
10–20 min
Final approach — cone 6 heat work
Why Fire Slowly at the Start?
Even bone-dry clay contains residual moisture. Firing too fast in the early stages traps steam inside the clay, which can cause pieces to crack or even explode. A slow initial ramp of 80–100°F/hour up to around 250°F gives moisture a chance to escape safely.
Quartz Inversion
At approximately 1063°F (573°C), silica in the clay undergoes a rapid phase change called quartz inversion. This causes a sudden expansion of the clay, which can crack pieces if the kiln heats or cools through this temperature too quickly. Both firing and cooling should be slow through this range — around 150–200°F/hour.
Holds at Peak Temperature
A hold at peak temperature (also called a soak) gives the kiln time to even out temperature variations between the top and bottom of the kiln, and allows glazes to fully melt and heal over any pinholes or surface defects. A 10–20 minute hold at cone 6 is standard for most electric kiln firings. For stubborn pinholes, extend the hold or slow the final ramp rate.
Cooling: Often Overlooked, Always Important
How you cool your kiln matters as much as how you fire it. Cooling too fast through quartz inversion (around 1063°F / 573°C) can crack even well-fired pieces. Most electric kilns cool naturally once the elements switch off — this is usually fine for standard firings. For thick-walled pieces, very large loads, or special glazes (like iron reds), a controlled slow cool can make a significant difference.
Never open your kiln above 200°F (93°C) — thermal shock from the sudden rush of cold air can crack both your pottery and the kiln’s firebrick. Wait until the kiln has fully cooled to room temperature before unloading.
Cone-Fire Mode vs Manual Programming
Most modern digital kiln controllers offer a cone-fire mode — you enter your target cone number and the controller runs a pre-programmed schedule designed for that cone. This is convenient for beginners, but the built-in schedules are often designed for slip casters and may fire faster than ideal for wheel-thrown or hand-built work with thick walls.
If you’re firing thick-walled pieces, heavily textured work, or large loads, consider programming a custom schedule with a slower initial ramp and a longer hold. Most experienced studio potters end up with their own tested firing schedule dialed in for their specific kiln, clay, and glazes.
Single vs Multiple Firings
Standard two-fire: Bisque to cone 04, glaze fire to your target cone. The most reliable approach for most studio work.
Single fire (once-fire): Raw clay glazed and fired in one firing. Saves time and kiln costs but requires careful technique — raw glaze on raw clay can crack and fall off during firing if not applied correctly.
Third fire: Used for overglaze decoration, lusters, and decals. Fired at a lower temperature (typically cone 018–022) after the standard glaze firing.
I am a visually impaired ceramic artist. I have been making for around 8 years now. I specialize in functional colorful pottery. Mainly nerikome and other decorative processes.
