How to Choose Between Single and Double Firing for Pottery Glaze

Pottery glazing is an art form that transforms the texture, color, and durability of ceramic pieces. One of the critical decisions potters face is whether to use a single firing or double firing process for applying glaze. Each method has its unique benefits and challenges, impacting both the aesthetic quality and functionality of the final product. This article delves deep into the distinctions between single and double firing, helping potters—from beginners to professionals—make informed decisions about their glazing techniques.

Understanding Firing in Pottery

Before dissecting single versus double firing, it’s essential to understand what firing entails in pottery. Firing is the process of heating clay objects in a kiln to solidify their shape and make them durable. When applying glaze, firing also melts the glaze into a smooth, glass-like surface that adheres to the pottery.

• Bisque Firing: The initial firing that turns the soft clay into ceramic by hardening it. This step removes water and organic materials.
• Glaze Firing: The second firing where the glaze melts and fuses onto the bisque ware, resulting in a finished surface.

In double firing, these two firings are separate, while in single firing, glaze is applied to raw (unfired) clay and fired only once.

What Is Single Firing?

Single firing is a technique where both the clay body and glaze are fired simultaneously in one single process. In this method, artists apply glaze to greenware (unfired pottery) or very slightly dried pieces and then fire them without prior bisque firing.

Advantages of Single Firing

1. Energy Efficient: Since only one firing is needed, this method saves time, energy, and kiln wear.
2. Less Handling: Pottery is handled fewer times, reducing breakage risk during transport from bisque to glaze application stages.
3. Faster Production: Suitable for commercial pottery production or artists with tight deadlines who want quicker turnaround.
4. Unique Effects: The interaction between raw clay and molten glaze can create interesting textures and finishes that differ from traditional double-fired ware.

Challenges of Single Firing

1. Fragility During Glazing: Greenware is fragile; applying glaze without breaking requires skillful handling.
2. Limited Glaze Choices: Some glazes are not compatible with direct-to-bisque application since they require the porous surface bisque firing provides.
3. Moisture Issues: The clay may absorb moisture from the glaze application process causing uneven drying or warping.
4. Risk of Defects: Problems such as crawling (glaze pulling away), pinholes, or blistering may be more common if the firing schedule isn’t carefully controlled.
5. Shrinkage Concerns: Clay shrinks as it dries; when glaze is applied on wet or leather-hard clay, uneven shrinkage can affect glaze adherence.

What Is Double Firing?

Double firing involves two separate firings: the first bisque firing to harden the pottery body followed by glazing and a second firing to mature the glaze surface.

Advantages of Double Firing

1. Durability: Bisque-fired pottery is strong enough for handling during glazing without breaking.
2. Porous Surface for Glaze: Bisque ware absorbs water from glazes easily, allowing for better adhesion and more consistent results.
3. Greater Glaze Variety: More types of glazes work well on bisque ware including those that require soaking or multiple layers.
4. Controlled Results: Potters can address defects after bisque firing before glazing; problems like cracks or warping become easier to correct.
5. Complex Decoration Opportunities: Techniques such as underglazing or overglazing are easier on bisqueware because surface texture and porosity aid paint adherence.

Challenges of Double Firing

1. More Time Consuming: Requires two kiln firings, making production slower.
2. Increased Energy Usage: More fuel or electricity consumption increases costs.
3. Additional Handling Risks: More handling between firings increases chance of damage.
4. Potential Warping or Cracking: Improper drying before bisque can cause issues that carry over into final pieces.

Factors to Consider When Choosing Between Single and Double Firing

When deciding which method suits your pottery project best, several factors should be considered:

Type of Clay Body

• Porous earthenware typically fares well with double firing due to its absorbency.
• Stoneware and porcelain clays may lend themselves better to single firing because they mature at higher temperatures with less absorption.

Desired Aesthetic Outcome

• If you want glossy, thick glazes with layered effects, double firing offers more control.
• For matte or textured finishes with natural clay-glaze interactions, single firing can yield unique results.

Production Volume

• High-volume commercial studios often prefer single firing for efficiency.
• Individual artists focusing on detailed decoration may choose double firing for precision.

Equipment Availability

• Access to kilns capable of precise temperature control influences choice; some glazes require specific ramps that are easier to manage in double firings.
• Kiln capacity limitations may encourage single firings.

Skill Level

• Beginners often learn double firing first because it allows fixing mistakes at bisque stage without losing entire pieces.
• Experienced potters confident in drying times and glaze chemistry might experiment with single firing for innovation.

Practical Tips for Successful Single Firing

If you decide to try single firing in your studio, here are some strategies to improve success rates:

• Use low absorption clays that tolerate direct glaze application.
• Apply thin layers of glaze to prevent trapping moisture.
• Allow greenware to dry thoroughly but not bone-dry before glazing (leather-hard stage).
• Test all glazes beforehand as many require adjustment for direct-to-bisque application.
• Control kiln ramp speeds carefully; fast heating can cause steam explosions inside greenware.
• Consider using wax resist or other techniques to prevent sticking during firing since pots haven’t been fired once already.

Practical Tips for Successful Double Firing

For those opting for double firings:

• Ensure complete drying before bisque firing to prevent cracking.
• Use appropriate bisque temperature (usually cone 06–04) depending on clay body.
• Inspect bisqueware carefully before glazing; repair any cracks if possible.
• Select glazes compatible with your bisqueware porosity level.
• Avoid overly thick glaze applications which can cause defects during second fire.
• Monitor kiln atmosphere during glaze fire (oxidation vs reduction) as it affects final colors.

Conclusion: Which Should You Choose?

Both single and double firing methods have their places in pottery glazing practices. Your choice depends largely on your production goals, type of clay and glazes used, equipment available, aesthetic preferences, and personal workflow comfort.

• Choose single firing if you aim for efficiency, want to reduce energy cost and handling risks, or desire creative textures unique to this method.
• Opt for double firing when you prioritize durability, need greater control over decoration details, work with delicate or absorbent clay bodies, or use specialized glazes better suited for bisqueware surfaces.

Experimentation remains essential—testing different approaches will deepen your understanding and refine your craftsmanship over time. Whether through one careful fire or two distinct ones, mastering your glazing method will elevate your pottery from functional vessels into lasting works of art.