Ceramics is not created by shaping and drying alone. It is the firing process that transforms clay into a durable, waterproof work of art. During firing, heat and time permanently alter the clay: organic components burn off, crystal structures change, glazes melt and bond with the body. Depending on what you want to fire, stoneware, porcelain, or earthenware, the duration, temperature, and procedure vary significantly.
This article summarizes what really happens during firing and helps you find the right technique for your projects. If you are still working on the potter's wheel or are interested in the basics of pottery, you can find an overview in our basic article Potter's Wheel: Basics, Types and What to Look Out For.
The Two Firing Stages
In ceramic firing, there are roughly two stages, each serving different purposes and therefore requiring different temperatures.
Bisque Firing: The Foundation for Everything Else
Bisque firing (sometimes also called biscuit firing) takes place at relatively low temperatures, usually between 900 °C and 1,000 °C. In this phase, the last remnants of water and organic components evaporate, and the clay becomes stable enough to be glazed. Bisque-fired pieces are porous, allowing glaze to adhere well.
Typical errors in this phase include explosions due to residual moisture (if clay is heated too quickly) or cracks due to uneven drying. To avoid this, pieces should be completely dry before bisque firing and the kiln should be ramped up slowly.
Glaze Firing: When Clay Bonds with Glass
After bisque firing, glaze firing follows: Here, the glazed pieces are brought to higher temperatures, depending on the glaze and clay type, between approximately 1,040 °C and 1,280 °C. The glaze melts, the body sinters (densifies), and the glaze and body bond.
There are countless glazes with different melting ranges. Therefore, always pay attention to the information provided by your glaze manufacturer and do not fire "by guesswork." Too high a temperature can cause glaze to run off the piece; glazes fired too low remain dull or rough.
Understanding Temperatures
Temperatures in the kiln are probably the most discussed topic. Not every clay tolerates the same temperatures and not every thermometer is accurate: Digital controls show a value, but the real temperature in the kiln can vary depending on the position. That's why many ceramists use cones made of special chamotte that melt at certain temperatures: This way, you can tell if the kiln has really reached the desired level.
What Temperatures Does Ceramics Really Need?
Clay types can be roughly divided into three firing ranges:
- Low-fire (earthenware): 900–1,050 °C – the body remains porous. Ideal for decorative pottery and flowerpots that do not need to be waterproof.
- Stoneware: 1,150–1,250 °C – the body becomes waterproof without glaze. Stoneware is robust and food-safe. Many hobby ceramists fire stoneware in the range around 1,200 °C.
- Porcelain: 1,250–1,300 °C – the finest, highest-fired clay. Porcelain requires careful temperature control and is more suitable for experienced ceramists.
In addition to the maximum temperature, the holding time – how long the kiln remains at the maximum temperature – is also important. Glazes often require a holding time of 10–30 minutes to melt evenly and cool without bubbles.
Firing Curves & Time: The Underestimated Factor
Many beginners believe that the final temperature is the most important thing. In practice, the heating and cooling rate is at least as important. During bisque firing, the kiln must be ramped up slowly so that water and chemically bound water can evaporate from the clay. Especially between 100 °C and 300 °C, heating is often too fast, which can lead to explosions.
Cooling should not be underestimated either: glazes do not like thermal shocks. Too rapid cooling can lead to tension in the glaze, which may only become visible days later in the form of fine cracks. Modern controls offer so-called ramp programs where you can define heating rates, holding times, and cooling rates.
Kiln Technology & Kiln Types
Today, most hobby ceramists will work with electric kilns. Gas and wood-fired kilns play a role more in specialized workshops, especially when reducing atmospheres are desired. For beginners, you should know what types of kilns exist and what that means in practice:
- Top-loader: Space-saving and often cheaper. Loading and unloading can be more strenuous with heavy pieces.
- Chamber kilns: Side door, more ergonomic, often more expensive – good for series production and larger pieces.
- Electric vs. Gas: Electric is simple, clean, and highly reproducible. Gas allows for special effects/atmospheres but requires installation and experience.
- Control: Rotary knobs vs. programmable controllers (firing curves, holding times, repeatability).
We carry both Kittec kilns and PyroTec kilns including accessories in our range. If you are looking for a new kiln, our guide will help you find the right model.
Kiln Selection: What Makes a Good Kiln?
When buying, price is not the only factor. Pay attention to:
- Insulation: The thickness and material of the firebrick ensure that the kiln maintains temperature and saves energy.
- Heating elements: Durable wires and good mounting reduce maintenance.
- Control & Repeatability: Programs store firing curves. Precise control makes results reproducible.
- Service: Spare parts, customer service, and repair options are invaluable.
- Size & Power Connection: Consider workpiece size and power supply (three-phase current for larger kilns).
Common Mistakes and Practical Tips
When firing, there are a number of pitfalls that occur repeatedly:
- Exploding pieces – almost always residual moisture. Allow to dry completely, do not "quick-dry."
- Cracks or warping – uneven thickness, too rapid heating or cooling.
- Running glazes – applied too thickly or fired too hot. Do tests, don't guess.
- Dull/rough glazes – fired too low or the glaze is intentionally matte; if necessary, check holding time/peak temperature.
Many experienced ceramists keep a firing log: temperatures, holding times, clay and glaze batches, special features. This way, you can find causes faster and repeat successful programs.
Home vs. Workshop: Environment, Safety & Coverage
At home, there are particular challenges: three-phase current is not always available, and the floor must be protected from heat and clay. Use heat protection plates or tiles under the kiln and plan for durable floor protection. Clay and glaze can permanently damage carpets.
Ensure good ventilation, as fumes can be generated during firing – especially during glaze firing. Place the kiln in a well-ventilated area and maintain safety distances. Fire extinguishers and smoke detectors should be a matter of course.
In workshops, the focus is more on efficiency: loading/unloading, capacity, and a clean workflow. The choice of kiln depends on whether you produce series or rather individual pieces/courses.
Checklist Before the First Firing
- Is the piece completely dry?
- Have you chosen clay and glaze suitable for the target temperature?
- Is the firing curve (heating, holding time, cooling) set?
- Is the kiln clean (no glaze residue on walls/shelf plates)?
- Have you addressed floor protection, heat clearance, and ventilation?
- Are you firing with others? Clearly mark your pieces.
- Does the power connection/fuse match the kiln?
- Clay water: Bucket/settling container prepared (not down the drain)?
FAQ
How long does a firing process take?
This depends on the kiln, the mass of the workpiece, and the temperature. A bisque firing at 950 °C often takes 8–12 hours (including heating and cooling). A glaze firing at 1,200 °C can take up to 24 hours. Do not open the kiln too early: too rapid cooling can cause damage.
Can I operate a kiln in my apartment?
Theoretically yes, practically only to a limited extent: You need a suitable electrical installation (often three-phase current), heat-resistant floor protection, and good ventilation. Be sure to clarify this with your landlord and insurance company. For many, a separate room or garage is more realistic.
Do I need a bisque firing if I fire at low temperatures?
Mostly yes. Bisque firing makes the body more stable, glaze adheres better, and the risk of bubbles decreases.
What are the most common mistakes in glaze firing?
Runs (too thick/too hot), dull glaze (too cold), bubbles (combination/program), and crazing (tension). Always test new glazes on test pieces first.
Further Reading
- Guide: Kittec Kilns – if you want to compare specific models.
- Ideas for Pottery: These Ceramic Pieces You Can Make Yourself – Inspiration for your next project.
- Pottery in Trend: Why Handmade is Inspiring Again Today – A look at the new developments in the ceramic scene.
- From Clay to Textile: Why Ceramists So Often Immerse Themselves in Other Crafts
- Buying a Potter's Wheel: Which One Suits Your Working Style?