How to Use Raw Glazes on Pottery

Raw glazing is an exciting technique in pottery that allows potters to apply glaze to unfired clay, combining the bisque and glaze firing into one process. This method saves time and energy while providing unique finishes that cannot always be achieved through traditional glazing methods. However, it requires an understanding of the materials and careful handling to ensure successful results. This guide will explore the fundamentals of how to use raw glazes on pottery, offering tips and techniques to help you master this innovative approach.

What is Raw Glazing?

Raw glazing is a pottery technique where glaze is applied directly to greenware, which is clay that has been shaped but not yet bisque fired. This method eliminates the need for a separate bisque firing, as both the clay and the glaze undergo their transformation in a single firing process. The applied glaze interacts directly with the raw clay, resulting in distinctive textures and finishes that are often unattainable through traditional methods.

While raw glazing can save time and resources, it requires a deep understanding of glaze chemistry, firing schedules, and meticulous craftsmanship to avoid issues such as bubbling, cracking, or uneven coverage. This innovative technique provides potters with both creative freedom and practical advantages when executed properly.

Preparing for Raw Glazing

Proper preparation is essential to achieve successful results with raw glazing. First, ensure that the surface of the unfired clay is clean and free of dust or debris, as these can interfere with the adhesion of the glaze. It’s also important to evaluate the moisture content of the clay body; overly dry pieces may absorb glaze unevenly, while excessively wet pieces can result in application inconsistencies. Selecting the right glaze formula is equally critical—opt for glazes specifically designed for raw application or those with a compatibility record for your chosen clay body.

Along with these preparations, testing small samples before glazing a full piece can help identify potential issues, allowing for adjustments to firing schedules or glaze mixtures as needed. By dedicating time to these preparatory steps, potters can set a strong foundation for a successful raw glazing process.

10 Methods How to Use Raw Glazes on Pottery

1. Understanding the Composition of Raw Glazes

Before applying raw glazes to pottery, it’s essential to understand their composition and how they differ from pre-mixed or fritted glazes. Raw glazes are made from unfired mineral ingredients—such as feldspar, clay, silica, and various oxides—that have not undergone any melting or pre-fusion. Because of this, they behave differently during both application and firing. The raw materials must be ground finely and accurately measured to ensure consistent results. Understanding the role of each ingredient helps potters tailor their glaze recipes to achieve specific surface qualities, such as matte, glossy, or satin finishes.

2. Sourcing and Weighing Raw Materials Precisely

The success of raw glaze application relies heavily on the careful sourcing and weighing of materials. Each component in a raw glaze recipe contributes a specific property—silica for glass formation, kaolin for suspension, fluxes like feldspar for melting, and coloring oxides for hue. All materials must be weighed using a precision scale to achieve consistent batches. Even small variations can drastically change the outcome, especially when working with reactive or reduction-sensitive oxides. Clean, labeled containers and an organized workspace help maintain accuracy and reduce contamination between batches.

3. Mixing the Glaze Slurry Thoroughly

Once raw materials are weighed, they need to be thoroughly mixed into a water-based slurry. This is often done using a powerful blender or a specialized mixer. The goal is to break down clumps, disperse particles evenly, and achieve a creamy consistency. Sifting through a fine mesh sieve—usually 80 to 100 mesh—is common practice to ensure homogeneity and remove larger particles that could cause surface defects. Since raw glazes contain clay, they can become thixotropic, meaning they gel when at rest but become fluid when stirred, which is ideal for dipping and brushing.

4. Choosing the Right Application Method

Raw glazes can be applied through various methods: dipping, pouring, spraying, or brushing. Dipping is the most common and provides even coverage, especially for functional wares. The piece is submerged in the glaze slurry for a few seconds and withdrawn smoothly to avoid streaks or air bubbles. Pouring is useful for inside surfaces or large forms. Brushing, although requiring more effort and multiple coats, allows detailed control and is ideal for smaller works. Spraying with a glaze gun offers gradient effects and layering potential but requires proper ventilation and a dust mask due to airborne particles.

5. Adjusting Water Content and Viscosity

One of the subtle arts of using raw glazes involves adjusting the water content and viscosity of the slurry. A glaze that is too thick will result in crawling, cracking, or an overly textured surface, while one that is too thin may lead to poor coverage and color dullness. Testing viscosity with a hydrometer or visually checking the thickness as it flows off a stir stick can help maintain consistency. Potters often keep a small test tile nearby to quickly assess coverage and drying behavior before applying it to final pieces.

6. Applying to Bone-Dry or Bisqued Pots

Raw glazes are versatile in that they can be applied either to bone-dry greenware or to bisqued pottery. When applied to greenware, the glaze and clay body shrink together during firing, which can result in strong bonding and less chance of pinholing. However, this method requires delicate handling since greenware is fragile. Applying to bisqued pots is more forgiving, and the absorbent surface helps the glaze adhere uniformly. Each method influences the glaze’s behavior during firing, so testing both approaches helps determine which best suits your aesthetic and workflow.

7. Layering and Texturing with Raw Glazes

One of the artistic advantages of raw glazes is the ability to layer different recipes for dynamic, multi-tonal effects. Potters often experiment by overlapping two or more raw glazes, allowing fluxes to interact and create variation. Some add texture to the pot’s surface before glazing so the raw glaze pools in grooves, accentuating details. Others sprinkle dry coloring oxides over the wet glaze to develop speckled or mottled surfaces. Because raw glazes tend to flux more naturally during firing, these layered effects can produce unexpected yet beautiful results with depth and complexity.

8. Handling Drying Time and Surface Cracking

Raw glazes may crack or shrink excessively while drying, especially if applied too thickly or to highly porous bisqueware. These cracks can lead to crawling or poor adhesion in the kiln. To minimize this, apply multiple thin coats rather than one thick layer and allow each coat to dry slightly in between. Keep the glazed pieces in a well-ventilated area to ensure even drying. Humidity and temperature also affect drying time, so adjusting your studio environment or drying strategy helps avoid premature defects before firing.

9. Firing with Care and Testing Often

Firing raw glazes requires a cautious approach, especially during the initial ramp-up phase of the kiln. Since raw glazes may contain organic binders or have higher moisture retention, too rapid a temperature increase can cause bubbling, pinholing, or even spalling. A slow bisque or combined bisque-glaze firing schedule is recommended if glazing greenware. Once in the glaze firing, understanding the cone rating and atmosphere—oxidation or reduction—plays a crucial role in achieving the desired finish. Testing small tiles with different kiln positions and firing schedules helps fine-tune the glaze behavior and avoid ruining large batches.

10. Keeping a Glaze Log and Iterating Recipes

Because raw glazes are so variable and sensitive to slight changes in materials, it is crucial to maintain a detailed glaze log. Record every batch’s exact composition, application method, drying conditions, and firing schedule. After firing, photograph and annotate results—identifying issues like crazing, pinholes, or color shifts. This documentation supports iterative improvement and helps replicate successful results. Over time, potters often tweak raw glaze recipes by substituting different fluxes or opacifiers to adapt to new clay bodies or desired effects, making the log a valuable reference and learning tool.

Things to Consider When Testing Glazes

When testing glazes, there are several factors to keep in mind to ensure consistent and reproducible results. First, always test on the same type of clay body that will be used in the final piece, as differences in clay composition can affect the glaze’s appearance and performance. Second, consider the thickness of glaze application; variations in thickness can lead to uneven results or defects such as dripping or crawling. It’s also crucial to maintain precise firing schedules, as temperature fluctuations or inconsistent kiln settings can dramatically alter the glaze outcome.

Finally, be mindful of safety, especially when working with potentially hazardous materials like silica or certain colorants, and ensure proper protective measures are in place. These considerations will help achieve reliable and high-quality results.

Conclusion

Working with raw glazes is both a technical and artistic endeavor. While they require more preparation and understanding than commercial or pre-melted glazes, they also offer unparalleled flexibility and creative control. From carefully measuring raw materials and adjusting viscosity to experimenting with layering and firing, each step shapes the final outcome. Thanks for reading our blog post on how to use raw glazes on pottery! We hope you found it helpful and informative.