Bisque vs glaze firing
Bisque firing hardens raw clay into porous, easy-to-handle ware, usually at a low cone like 06 or 04, with a slow early ramp so water and organics leave safely. Glaze firing melts the glaze onto already-bisqued ware, often hotter, with a hold near the top to smooth the surface.
| Bisque firing | Glaze firing | |
|---|---|---|
| Goal | Harden raw clay into porous, handleable ware | Melt glaze to a smooth, sealed surface |
| Typical cone | 06 to 04 (low fire) | 06 to 04 low fire, or 5 to 6 mid, or 9 to 10 high |
| Early ramp | Slow, to drive off water and burn organics | Can be quicker, the body is already dry and clean |
| Candle | Important, especially on thick or damp ware | Brief, mostly to clear surface moisture |
| Top hold | Usually none | A short hold helps the melt smooth and heal |
| State after | Porous bisqueware, ready to glaze | Finished, food-safe where the glaze allows |
Why bisque ramps slower
Raw clay holds water you cannot see and organic matter from the clay body. Heat it too fast and that water flashes to steam inside the wall, which can crack or even explode a pot. A bisque schedule therefore opens with a gentle climb, often near 80 F per hour to 250 F with a candle, then eases through the burnout and quartz-inversion zones before reaching the cone. A common slow bisque to cone 04 runs about 13 hours.
The standard slow bisque program built into Bartlett, Skutt, and L&L controllers ramps at 80 F/hr to 250 F, 200 F/hr to 1000 F, 100 F/hr to 1100 F, 180 F/hr to 1695 F, then 80 F/hr to the cone. That is the shape this site's bisque schedules follow.
Source: Bartlett factory cone-fire programs, reproduced by SDS Industries (kilncontrol.com) and Ceramic Arts Network.Why glaze firings add a hold
By the glaze firing the body is already bisqued, so the early ramp can move a bit faster. The interest is at the top: glazes melt and flow in the last stretch, and a short hold, often five to fifteen minutes, gives the melt time to level out and heal small pinholes and blisters. For glossy glazes that pinhole, a controlled drop-and-hold, cooling fast just below peak and soaking, works even better. The schedule builder offers that as an option on glaze firings.
Pick your firing and build the schedule
Choose bisque or glaze in the builder, set your cone and speed, and it lays out the right ramps and holds for that firing type, with the peak read from the Orton cone chart.
Sources
- Orton pyrometric cone temperature chart, ortonceramic.com.
- Bartlett / Skutt / L&L cone-fire factory programs (SDS Industries, kilncontrol.com; skutt.com; hotkilns.com).
- Drop-and-hold rationale: digitalfire.com, PLC6DS schedule.
Frequently asked questions
Do I bisque fire before glazing?
Almost always, yes. Bisque firing turns fragile greenware into porous, sturdy ware that is easy to handle and that soaks up glaze evenly. You can single-fire raw-glazed greenware, but it is harder, so most studios bisque first, usually to cone 06 or 04, then glaze fire.
Why is bisque often fired hotter than the glaze?
It is common to bisque at cone 04 and glaze low-fire ware at cone 06, so the bisque is the hotter of the two. That makes the bisque body slightly less absorbent and more durable, while the lower glaze firing protects bright low-fire glaze colors. For mid and high fire, the glaze firing is the hotter one.
Can I bisque and glaze in one firing?
Single firing is possible and saves time and energy, but it demands a careful schedule: a slow early ramp to clear water and organics from the raw clay, then the glaze maturity climb. Most beginners get more reliable results bisquing separately first.