Why the controller is your kiln's brain

Your kiln controller does far more than switch elements on and off. It manages the entire firing curve — the carefully planned journey from room temperature to peak and back down again. For a home studio potter, understanding ramp, soak and cooling settings turns a mysterious box of buttons into a powerful tool. You can adjust results for different clay bodies, fix glaze faults, and fire more safely. This article explains the key terms and how to use them, without needing a degree in thermodynamics.

Ramp, soak and cooling: the three building blocks

Every firing program is built from three basic actions. A ramp is the rate at which the kiln heats or cools, usually measured in degrees Celsius per hour (°C/hr). For example, a ramp of 100°C/hr means the kiln takes one hour to rise from 20°C to 120°C. A soak (also called a hold or dwell) keeps the kiln at a constant temperature for a set time, allowing heat to even out and chemical reactions to complete. Cooling can be natural (the kiln switches off and cools on its own) or controlled, where the controller follows a set ramp downwards.

A typical program is a series of segments. Each segment has a target temperature, a ramp rate, and a soak time. For instance:

• Segment 1: ramp at 100°C/hr to 600°C, soak 0 minutes.
• Segment 2: ramp at 150°C/hr to 1000°C, soak 10 minutes.
• Segment 3: ramp at 80°C/hr to 1220°C, soak 30 minutes.
• Segment 4: controlled cooling at 150°C/hr to 800°C, then natural cooling.

Your controller may allow 10, 20 or more segments. Don't feel you must use them all. Simple is safe.

Choosing a schedule for your clay body

Clay bodies have different demands. Earthenware matures around 1060–1120°C and can tolerate faster firing, but it still needs a slow start to drive off mechanical water. Stoneware and porcelain need more careful heating, especially through the quartz inversion at 573°C. At this point, silica crystals change structure, and a ramp faster than 150°C/hr can crack thick or uneven pots. Porcelain often benefits from a slower ramp above 1100°C to avoid bloating.

Bisque firing is usually slower than glaze firing. A common bisque schedule: 80°C/hr to 120°C, soak 30 minutes to dry thoroughly; then 120°C/hr to 573°C, soak 10 minutes; then 150°C/hr to 1000°C, soak 20 minutes. Glaze firing can be faster, but a 30-minute soak at top temperature helps glazes melt smoothly and reduces pinholing.

Always check your clay supplier's recommended firing curve. If none is available, start with a conservative schedule: 100°C/hr to 600°C, 150°C/hr to peak, 30-minute soak, and controlled cooling at 100°C/hr to 800°C. Adjust from there.

Fine-tuning for glaze results

Soak and cooling settings are your secret weapons for glaze finish. A longer soak at peak temperature increases heat work, making glazes more fluid and glossy. If your glaze is dry or immature, add 10–15 minutes soak or raise peak by 10°C. If it runs off the pot, reduce soak or lower peak.

Cooling rate changes crystal growth. Slow cooling (e.g. 60°C/hr between 1100°C and 900°C) encourages matte, crystalline or satin surfaces. Fast cooling (natural, or 200°C/hr) gives bright, glossy results. For pinholing, try a drop-and-hold: after peak, cool rapidly to 1100°C, then soak for 30 minutes. This lets bubbles escape before the glaze stiffens.

Keep detailed notes. Fire test tiles with each adjustment. Change only one variable at a time — soak length, then cooling rate — so you know what caused the difference.

Safety, testing and record keeping

Never fire a kiln without ventilation. Even electric kilns release fumes from clay and glaze materials. Place your kiln in a well-ventilated area, use a downdraught vent if possible, and never leave a firing completely unattended. Use witness cones on the shelf to confirm your controller's readings. Controllers can drift; cones tell the truth.

Keep a firing log. Record program number, clay body, glaze, peak temperature, soak time, cooling rate, and results. After a few firings, you'll see patterns. Also, respect your kiln's limits — don't ramp faster than the elements can handle, usually 999°C/hr maximum but practically 200–300°C/hr for most home kilns.

Putting it into practice

Start with a simple, conservative program for each clay body. Fire a few test pieces. Then adjust one setting at a time. Over a few weeks, you'll build a personal library of programs that suit your work. Understanding ramp, soak and cooling gives you confidence to experiment safely — and that's when home firing becomes truly rewarding.