Bisque firing schedule explained

A bisque firing schedule heats raw clay slowly so water, carbon, and sulfur leave before the clay starts to seal, then stops at a low cone, usually 06 or 04. The slow program to cone 04 runs five ramps over about 13 hours and peaks at 1945 F (1063 C).

Updated October 28, 2026 · Source: Ceramic Arts Network, Bisque Firing 101

What does a bisque firing schedule look like?

It's five ramps, and each one is set by what the clay is losing at that temperature. Below is the slow cone 04 program the firing schedule builder writes when you pick bisque. Its shape is the Bartlett factory slow bisque, a preset on Bartlett kiln controllers, and the peak comes from Orton's cone chart.

That's 13 hours 22 minutes from a 75 F start in an empty kiln. Bartlett's own listing of the program, published on Digitalfire as BTSB04, stops at 1926 F instead, 19 degrees lower. Orton's 1945 F assumes the last stretch climbs at 108 F per hour, and a slower finish bends the same cone at a lower temperature, so both numbers are in the right place. Put a witness cone on the middle shelf and let it settle the question for your kiln.

What happens to the clay at each temperature?

Clay gives up something different in each band, and the ramps are set around them. The ranges below come from three Ceramic Arts Network articles. They disagree by up to a couple hundred degrees in places, so read them as bands.

The last two rows cause trouble later. Davis explains that once black iron oxide starts fluxing the wall at about 1650 F, any carbon or sulfur still inside is trapped. You won't see it at the bisque. You see it in the glaze firing, when the wall softens and the trapped gas swells into bloats. He also gives sulfur a range that runs up to 2102 F (1150 C), well past any bisque peak.

So segment 4 is where a bisque earns its keep. The slow program spends 2 hours crossing 1292 to 1652 F, medium about 1 hour 26 minutes, fast about an hour. High-iron clays, thick pieces, and packed shelves want the slow end, and Davis says the kiln must be well vented through that band. If you're already finding bloats or grey cores, the guide to kiln firing problems matches each fault to the segment to change.

Do you need to slow down for quartz inversion in a bisque?

Not much. Finkelnburg writes that damage at quartz inversion, about 1063 F (573 C), is a concern mainly when dense ware cools. Bisque ware is porous on the way up and on the way down. Tony Hansen's Plainsman bisque schedule on Digitalfire climbs straight through at 306 F per hour, and he reports that quartz inversion hasn't been a problem in their bisque firings, heating or cooling.

The builder still slows to 100 F per hour from 1000 to 1100 F, because the Bartlett program does. It costs an hour on slow, 50 minutes on medium, and 40 on fast. Keep it for thick sculpture or a mixed load of thick and thin. For thin, even ware, it's the first segment you can speed up on your controller.

Slow, medium, or fast: which bisque speed should you use?

Use slow for pieces about 1/2 inch thick or 15 inches or more in any direction, and medium for everyday ware 3/8 inch thick or less. Skip fast. That's Skutt's guidance for its own kilns, and its loading guide says the fast setting isn't recommended for most bisque firings.

Here's what the builder writes for cone 04 at each speed. Rates are in F per hour, targets in F.

The fast peak is higher because a 200 F per hour finish reads Orton's 270 F per hour column, where cone 04 bends at 1971 F. Cooling roughly doubles all of these, as the guide to how long a firing takes explains.

Speed is less dangerous than water. Larry Camm, writing in Ceramics Monthly, described an industrial test on 24 tiles, each 13 1/2 inches square and 3/4 inch thick. Bone dry, all 24 survived a 2 hour firing to cone 5, with only 15 minutes from room temperature to 1000 F. At 2% water, all 24 were lost. His take for studio kilns: a four hour bisque to cone 08 is reasonable only for work at zero moisture.

Hansen's BQ1000 schedule shows the other way to buy safety. It holds at 248 F as long as the ware needs, from one hour for light pieces to ten for heavy ones, then climbs at 306 F per hour to 1733 F and finishes at 108 F per hour to 1832 F (1000 C) with a 15 minute hold. With a one hour water hold it's done in 7 hours 44 minutes. The long hold does the job of the slow first segment. For how long to hold, see the candling and preheating guide.

Which cone should you bisque to?

Cone 06 or 04 for most studio work. Jeff Zamek, in Ceramics Monthly's Techno File column, says most stoneware and low-fire bodies can bisque at cone 06, with porcelain a little higher at cone 04. Finkelnburg calls cone 08 to 04 the common range for work that will be glazed at cone 5 or above.

Going hotter burns out more and gives a stronger, less thirsty pot. Going cooler leaves the bisque more porous, so glaze soaks in faster and goes on thicker. Hansen's rule at Plainsman is to bisque as hot as you can while glaze still goes on well. If pieces break while you glaze them, bisque hotter. If glaze goes on thin over a hot bisque, check the glaze's specific gravity before you drop the cone. Zamek adds that missing your bisque cone by one or two, anywhere between cone 010 and 04, won't change glaze absorption much.

Why do low-fire potters bisque hotter than they glaze?

To get the gas out first. Mayco's Stroke & Coat directions start from a cone 04 bisque and glaze at cone 06, and Speedball makes its earthenware glazes for ware bisqued to 04 and glazed at 05 or 06. Anything the bisque didn't burn out has to pass through the melting glaze later.

Hansen weighed it. The same clay lost 4.45% of its weight at cone 04 and 4.54% at cone 03. On a 250 gram mug that gap is about 0.2 grams, which sounds like nothing. Converted at the weight of air, he puts it near 170 cc of gas that would bubble up through the glaze if you bisqued at 04 and glazed at 03. Bisque at or above your low-fire glaze cone and that gas is gone before the glaze goes on.

How should you load and vent a bisque kiln?

Pack it tight. Bisque pieces can touch, stack rim to rim or foot to foot, and nest, because there's no glaze to fuse them. Put the heavy pieces at the bottom, keep every stack clear of the thermocouple, and leave room at the elements.

• Keep pots at least 1/4 inch (6.5 mm) from the elements. That's Zamek's minimum for electric kilns.
• Leave about 2 inches clear around the thermocouple tip and about an inch between shelf edges and the wall, per Skutt's loading guide.
• When you nest, rest the foot of the smaller pot on the floor of the bigger one. Don't hang its weight on the lower pot's rim.
• Give a dense load more time. Zamek warns that thick pieces and tight stacks, like tiles, trap carbon more often, so a packed kiln wants the slow program.

Then vent. Finkelnburg says ventilation matters from about 450 F, when organics start to burn, and again later, when sulfur leaves as sulfur trioxide and turns into irritating sulfuric acid. Run a downdraft vent for the whole bisque. If you don't have one, Hansen suggests propping the lid through the early stages for heavy loads and keeping air moving to red heat and past, so iron in the body stays oxidized.

How do you know the bisque came out right?

Check the witness cone first, then the pots. A self-supporting cone 04 that's bent until its tip is level with its base means the kiln did its heat-work. After that, handle the ware and look at the color.

• Even color. Hansen reads patchy color across a bisque load as incomplete oxidation. Without a vent, slow the middle of the climb (segments 2 and 4) next time.
• Strength. A good bisque survives handling through glazing. If rims chip or pieces snap, go a cone hotter.
• Absorbency. Glaze should coat at its usual thickness in a normal dip. If a glaze at the right specific gravity still goes on thin, the bisque ran too hot.
• Sound pieces. A crack or a blowout near the start of the firing points at water, not the cone. Add a hold to segment 1.

Build your bisque schedule

Pick bisque in the firing schedule builder, set your cone and speed, and it writes all five segments in F or C with the time to peak, then prints a sheet to tape to the kiln. The builder doesn't add a water hold, so for a thick or slightly damp load, add one to segment 1 on your controller before you press start.

Sources

• Dave Finkelnburg, Bisque Firing 101, Ceramics Monthly (ceramicartsnetwork.org).
• Jeff Zamek, Techno File: Bisque Firing, Ceramics Monthly (ceramicartsnetwork.org).
• Steve Davis, A Bisque Firing Schedule to Help Prevent Glaze Faults, Pottery Making Illustrated (ceramicartsnetwork.org).
• Larry Camm, Techno File: Rapid Bisque Firing, Ceramics Monthly (ceramicartsnetwork.org).
• Tony Hansen, Digitalfire firing schedules BTSB04 (Bartlett Slow Bisque Cone 04) and BQ1000 (Plainsman Electric Bisque Firing Schedule), with the cone 03 and 04 weight-loss test (digitalfire.com).
• Skutt Kilns, Best Practices for Loading and Firing Your Skutt Kiln (skutt.com).
• Mayco, Stroke & Coat directions (maycocolors.com), and Speedball earthenware glaze directions.
• Orton self-supporting cone temperature chart, 108 F and 270 F per hour columns (ortonceramic.com).