Kiln-dergarten: A Beginner’s Guide to Firing

So, you’ve molded your clay, perfected your glazes, and now it’s time for the grand finale: the firing! But hold on to your hats, because the kiln can be a mysterious beast with its own set of rules and quirks. 

Fear not, fellow clay enthusiasts! We’re here to demystify the firing process and guide you through the different types of kilns, from electric to gas, oxidation to reduction. 

Get ready to fire up your creativity (and your kiln)!

Kiln Types: A Quick Overview

Before we dive into the nitty-gritty, let’s break down the main types of kilns:

• Electric Kilns: These kilns are powered by electricity and are generally easier to use and maintain. They’re a popular choice for beginners and home studios.
• Gas Kilns: Gas kilns use natural gas or propane for fuel and offer more control over the firing atmosphere. They’re often favored by experienced potters and those seeking specific glaze effects.
• Wood-Fired Kilns: These ancient kilns rely on wood as fuel, creating unique ash glazes and unpredictable, beautiful results due to the interaction of flame and ash with the ware. They require significant time and effort to fire.
• Raku Kilns: Often smaller and portable, Raku kilns are designed for a rapid firing process. Pieces are removed from the kiln while still hot and subjected to post-firing reduction in combustible materials, producing dramatic, often metallic, effects.

CMW Blogs now have a new search feature! Read ALL CMW blogs about kilns now!

Oxidation vs. Reduction: It’s All About the Atmosphere

Now, let’s talk about the atmosphere inside the kiln. This plays a crucial role in how your clay and glazes turn out.

• Oxidation Firing: In an oxidation firing, there’s plenty of oxygen present in the kiln. This creates a consistent, predictable environment and allows for bright, vibrant glaze colors. Electric kilns naturally fire in oxidation.
  • Did you know? Many commercial glazes are formulated specifically to look their best in an oxidation firing, as the presence of oxygen allows certain metallic oxides in the glaze to develop their intended colors.

(This is an example of Oxidation vs. Reduction firing from Digital Fire)

• Reduction Firing: In a reduction firing, the oxygen supply is limited. This creates a smoky, oxygen-hungry atmosphere that can produce unique glaze effects, such as copper reds and iron saturates. Gas kilns are typically used for reduction firing.
  • Did you know? The lack of oxygen in reduction firing forces metallic oxides in the glazes to give up some of their oxygen, leading to chemical changes that result in rich, earthy tones and often surprising color shifts. For example, copper carbonate, which typically produces green in oxidation, can turn beautiful reds and purples in reduction.

Electric Kilns: Plug and Play Pottery

Electric kilns are like the easy-bake ovens of the ceramics world. They’re user-friendly, relatively low-maintenance, and perfect for beginners.

• Pros: Consistent temperatures, easy to operate, clean burning, precise temperature control through digital controllers, ideal for consistent results.
• Cons: Can be more expensive to operate than gas kilns (depending on electricity costs), limited atmospheric control (though “reduction” can be simulated with specific methods like introducing carbonaceous materials).

Most modern electric kilns come equipped with programmable controllers that allow for precise temperature ramp-ups and soak times, making the firing process incredibly consistent and hands-off once programmed. They often use heating elements made of Kanthal wire.

Freddy Fredrickson swears by electric kilns! Read more about his deep dive!

Gas Kilns: Firing Up the Excitement

Gas kilns offer more flexibility and control over the firing process, making them a favorite among experienced potters.

• Pros: Can achieve higher temperatures, allows for true reduction firing, potentially more economical to operate (depending on gas prices), ability to manipulate flame and airflow for unique effects.
• Cons: Requires more skill and knowledge to operate, can produce harmful emissions (requiring proper ventilation and sometimes afterburners), less precise temperature control compared to digital electric kilns.

Gas kilns often have multiple burners and damper systems that allow the potter to finely tune the atmosphere within the kiln, creating specific effects in glazes and clay bodies that are impossible to achieve in an electric kiln. The placement of ware within a gas kiln can also significantly impact the final outcome due to varying flame paths.

Wood-Fired Kilns: The Art of the Flame

Wood-fired kilns are among the oldest forms of ceramic firing. The firing process is labor-intensive, requiring constant stoking and attention to the firebox for days. The ash from the burning wood lands on the pottery, creating natural ash glazes that are unique to each firing and location within the kiln.

(This image is from Wood Fire Ceramic where they DIYs their own wood kiln!)

The unpredictable nature of wood firing is part of its appeal, leading to results that are deeply connected to the firing process itself and the interaction between the flame, ash, and ceramic materials.

Raku Kilns: The Thrill of Rapid Fire

Raku firing is characterized by its rapid heating and cooling cycles. Once the glaze reaches maturity (often in less than an hour), the glowing hot pottery is removed from the kiln and immediately placed into a reduction chamber (like a metal can with combustible materials such as sawdust or leaves).

The thermal shock and subsequent reduction process create unique crackle patterns, iridescent sheens, and metallic lusters in the glazes, making each Raku piece a one-of-a-kind creation.

(This image is owned by Pottery Crafters!)

Kiln FAQs:

• “Which type of kiln is right for me?” If you’re a beginner, an electric kiln is a great starting point for its ease of use and consistent results. If you’re looking for more atmospheric control, higher temperatures, or the unique effects of reduction, a gas kiln might be a better choice. For an adventurous and artistic challenge, consider exploring wood or Raku firing.
• “Can I do reduction firing in an electric kiln?” While electric kilns naturally fire in oxidation, there are ways to simulate a reduction atmosphere using special techniques and materials like carbon biscuits or placing pieces in saggar boxes with combustibles. However, these are approximations and won’t achieve the same depth of reduction as a dedicated gas kiln.
• “What safety precautions should I take when firing a kiln?” Always follow the manufacturer’s instructions and ensure proper ventilation to exhaust fumes and heat. Wear heat-resistant gloves and eye protection when loading, unloading, or interacting with a hot kiln. Never leave a firing kiln unattended, especially gas or wood kilns. Be aware of the extremely high temperatures involved and the potential for burns.
• “How do I know when my kiln has reached the correct temperature?” Kilns use pyrometric cones, which are small ceramic cones formulated to bend and melt at specific temperatures. These act as visual indicators of heatwork (the combined effect of temperature and time), giving you an accurate picture of what’s happening inside the kiln, in addition to digital readouts.
• “What is ‘candling’?” Candling is a slow, initial heating process (often below 200°F or 93°C) that allows all moisture to escape from the clay body before the main firing begins. This prevents steam from building up and potentially exploding pieces, especially for thicker forms.

Remember: Firing is a crucial step in the pottery process, and understanding the different types of kilns and firing atmospheres can help you achieve the results you desire. So, embrace the heat, experiment with different techniques, and watch your ceramic creations come to life!

CMW Blogs now have a new search feature! Read ALL CMW blogs about kilns now!

Join Our Patreon Community!

Love diving deep into the world of ceramics with us? If you’re passionate about clay and eager to take your skills and connections to the next level, consider becoming a patron! Our Patreon community offers an exclusive hub for dedicated potters like you. You’ll gain access to extra, free resource content to expand your knowledge, and we love to shine a light on our supporters with regular supporter spotlights, advertising your incredible work to our audience.

But perhaps the most popular perk is our live Q&A sessions, where you can directly ask Matt all your burning ceramics questions!!

Join our growing family today and let’s create something amazing together!

JOIN OUR PATREON NOW!

Ready to dive deeper?

Loved learning about ceramic glazes? Want to go even deeper? Check out our Workshops & Courses, now available in Spanish, or YouTube Channel where Matt breaks it all down, myth-busting and Stull chart included!