Bisque Firing Explained

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Bisque pottery is clay that has been fired once, at a relatively low temperature, before it's glazed. That first firing, the bisque firing, turns fragile greenware into hard, porous ceramic that can be handled without breaking and that soaks up glaze evenly. Most potters bisque fire to cone 04, about 1945°F (1063°C) per AMACO, then glaze and fire a second time to the clay's maturing temperature.

The bisque firing also burns out organic material and drives off water and gases that would otherwise cause defects in the glaze. Get it right and glazing goes smoothly. Rush it, and you'll see cracks, explosions, pinholes and crawling.

This guide explains what happens in a bisque firing, which cone to choose, and how to dry, load, preheat and fire a bisque load. The firing guidance comes from L&L Kilns, Mayco and Digitalfire.

What happens to bisque pottery in the kiln

Digitalfire describes bisque as a prefiring that makes ware resistant to handling damage and able to absorb water from the glaze slurry. It notes bisque porosity is generally more than 15%, which is why glaze dries so quickly on bisqueware.

What cone to bisque fire to

There's no single right answer, but there is a standard.

• Cone 04 (about 1945°F, 1063°C). The most common choice. AMACO lists cone 04 bisque for its Potter's Choice, Celadon and Teacher's Palette glazes, and Mayco's stoneware guidance uses bisque soft-fired to cone 04.
• Cone 06 (about 1826°F, 998°C per Mayco). Gives a more porous, absorbent bisque that takes glaze faster. Some potters prefer it for dipping thin glazes.
• Hotter bisque (cone 03–02). Some stoneware potters bisque hotter to burn off more gas and reduce pinholes. Digitalfire notes that firing bisque one cone hotter eliminated crazing on a low-fire body in one test, because the denser body "puts the squeeze" on the glaze. The trade-off is less absorbent bisque, so glaze goes on thinner and dries slower.

For low-fire work, keep a gap between bisque and glaze firings. Mayco recommends a two-cone difference, such as a cone 04 bisque with a cone 06 glaze firing, and links bisque and glaze temperatures that are too close with pinholes. In other words, for low-fire ware, the bisque is fired hotter than the glaze.

For mid-fire stoneware, the glaze firing at cone 5–6 is much hotter than the bisque. Digitalfire notes that stoneware glaze fit isn't affected by a hotter bisque, because the glaze firing goes so far beyond it.

How to bisque fire pottery: step by step

1. Make sure the ware is bone dry. Bone-dry clay is lighter in color and no longer feels cool against your cheek. Cool means moisture is still evaporating. Thick pieces, bottoms and handles dry last.

2. Check pieces for cracks. Cracks in greenware get bigger in the kiln. Repair or reclaim them now.

3. Load the kiln. Greenware can touch and stack, which is the big difference from a glaze firing. L&L says greenware can touch other pieces. Nest small bowls inside larger ones, stack plates rim to rim, and put heavier pieces on lower shelves. L&L's general loading guidance still applies: put the bottom shelf on 1/2-inch posts rather than on the kiln floor, use three posts per shelf set about an inch in from the edge, keep about an inch of clearance around thermocouples, and leave at least 1/2 inch between the tallest piece and the lid.

4. Add witness cones. Place a cone pack where you can see it through a peephole, or on a shelf to check after firing. Coyote and L&L both recommend witness cones to confirm what the kiln actually did, because thermocouples drift over time.

5. Preheat (candle) if there's any doubt about dryness. A preheat holds the kiln below the boiling point of water so remaining moisture leaves gently. L&L's DynaTrol preheat ramps at 60°F (33°C) per hour to 200°F (93°C), then holds for the time you set. In its advice on pinholes, L&L gives an example preheat of 40°F per hour to 200°F with a hold of one to two hours. Thick work needs longer.

6. Vent the kiln, or prop the lid early in the firing. Water vapor and fumes leave the clay early in the firing. L&L's advice: if a mirror held over the peephole fogs up even with the vent on, prop the lid about 1/2 inch with a piece of ceramic for the first few hundred degrees. L&L also states that kiln fumes, including carbon monoxide, must be vented outside.

7. Choose a slow bisque program. L&L calls Slow Bisque "the safest to use," because it gives fumes and water vapor more time to escape. It also says the more carbon-containing material you burn out during the bisque, the less outgassing and pitting you'll see in the glaze. L&L suggests starting with Slow Bisque and experimenting with faster programs later, mainly for very thin work.

8. Let it cool fully before opening. Opening a hot kiln stresses pieces. Mayco links opening the kiln too soon with crazing, and recommends cooling to 150°F (66°C) or lower before you open it. Room temperature is better.

9. Unload, inspect and store clean. Bisque picks up dust and skin oils easily, and both cause glaze problems later. Store it covered, and wipe it with a damp sponge right before glazing. Our how to glaze pottery guide takes it from there.

What a slow bisque schedule looks like

Most digital kilns include a preset slow bisque. To show what's inside one, here is L&L's published Easy-Fire Slow Bisque profile for cone 07 on its DynaTrol controller:

L&L notes its profiles are written for the fastest possible empty kiln, that a loaded kiln can take considerably longer (up to four times the times shown), and that the controller adjusts the final temperature to hit the cone's heat work. The pattern matters more than the numbers: slow at the start, a slower stretch around 1000–1100°F, and a slow final climb.

For a cone 05 bisque on clay that pinholes, L&L gives this slower custom example: 80°F per hour to 250°F, 200°F per hour to 1000°F, 100°F per hour to 1641°F, then 80°F per hour to 1891°F. Use your own kiln's manual and controller presets for the cone you need. Don't copy a schedule from another kiln without checking it.

Heat work: why time matters as much as temperature

A cone measures heat work, which is temperature combined with time. L&L explains it plainly: you can reach the same cone by firing slower to a lower temperature. That's why a long hold at the top can overfire ware. L&L says a 10-minute hold at the end adds about half a cone. It also notes that long holds shorten element life. Kilns held 20 minutes at temperature typically get about half as many firings as kilns that aren't.

For bisque, you rarely need a long hold at the top. Slower ramps earlier in the firing do more good.

Common bisque firing problems

Can you skip the bisque firing?

Some potters single-fire, glazing greenware and firing it once. It saves energy and time, but it's harder: raw clay is fragile, it absorbs glaze unevenly, and glazes made for bisque can crack or flake as the clay shrinks. Mayco's Stroke & Coat is one of the few commercial glazes the maker says can be applied to wet clay as well as bisque. For beginners, bisque firing is the reliable path.

Do you need your own kiln for bisque?

No. Community studios and clay suppliers often fire bisque for customers. If you want your own, a small kiln is enough for bisque. See our small pottery kiln guide, our home studio kiln picks and our breakdown of how much a pottery kiln costs. Your clay type matters too, and our stoneware vs earthenware vs porcelain guide explains how each behaves through both firings.

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