8.2: Glaze Characteristics and Types

Characteristics

Transparent Glazes

- Characteristics: Allow the underlying surface or decoration to show through; available in glossy, satin, or matte finishes.

- Common Uses: Highlight surface textures, carved designs, or underglaze patterns.

Opaque Glazes

- Characteristics: Completely cover the surface, obscuring any texture or decoration beneath.

- Common Uses: Create bold, solid colors or uniform finishes.

Ash Glaze

- Characteristics: Historically made with wood ash, these glazes produce a natural, flowing effect. Modern ash glazes use substitutes to mimic this traditional look.

- Common Uses: Rustic, organic pottery; associated with wood-fired kilns.

Salt Glaze

- Characteristics: Created by introducing salt into the kiln during firing, which reacts with silica in the clay to form a thin, textured glaze.

- Common Uses: Functional pottery with a distinctive, slightly orange-peel surface.

Alkaline Glaze

- Characteristics: High in alkaline fluxes like soda or potash, creating glossy finishes with soft, fluid textures.

- Common Uses: Traditional forms, often paired with natural clay bodies.

Celadon Variants

- Characteristics: Transparent glazes in hues of pale green, blue, or gray; often influenced by slight variations in iron oxide content and firing conditions.

- Common Uses: Highlight fine details on porcelain or white clay.

Copper Red (Sang de Boeuf)

- Characteristics: Intense red or burgundy hues achieved in reduction firings. Copper oxides are key to this glaze type.

- Common Uses: Decorative and high-end ceramic pieces.

Iron Glazes

- Characteristics: Iron oxide-rich glazes produce earthy tones such as brown, amber, or rust. Effects can vary with firing atmosphere and temperature.

- Common Uses: Rustic pottery and functional ware.

Cobalt Blue

- Characteristics: Vibrant, deep blue color achieved with cobalt oxide or carbonate.

- Common Uses: Decorative pieces and traditional ceramics, including Delftware and Chinese porcelain.

Zinc Crystal Glaze

- Characteristics: Encourages large crystals to grow within the glaze during a controlled cooling cycle.

- Common Uses: Decorative work, especially on sculptural ceramics.

Satin Glaze

- Characteristics: Offers a finish between glossy and matte, with a soft sheen.

- Common Uses: Adds subtle elegance to functional or decorative pieces.

Metallic Glazes

- Characteristics: Create shiny, reflective surfaces, often with gold, bronze, or silver tones. Many require post-firing applications like lusters.

- Common Uses: Highlight accents or decorative elements.

Speckled Glaze

- Characteristics: Contains small particles that create specks or flecks on the surface, adding depth and texture.

- Common Uses: Decorative functional ware, emphasizing rustic or natural aesthetics.

Oil Spot Glaze

- Characteristics: Produces spots or patches resembling oil on water. Created by excess iron in the glaze bubbling during firing.

- Common Uses: Traditional East Asian ceramics.

Carbon Trap Glaze

- Characteristics: Traps carbon during reduction firing, creating smoky, dark effects on the surface.

- Common Uses: Wood-fired and Shino-style pottery.

Crawling Glaze

- Characteristics: A glaze defect (often intentional) where the glaze pulls away from the surface, creating bare patches.

- Common Uses: Abstract or experimental ceramics.

Opalescent Glaze

- Characteristics: Iridescent and luminous, with shifting colors depending on light and thickness.

- Common Uses: Decorative and sculptural pieces.

Dry Matte Glaze

- Characteristics: Extremely matte and non-reflective; can have a powdery or textured finish.

- Common Uses: Sculptural ceramics or pieces emphasizing form over function.

Reduction Glazes

- Characteristics: Fired in a reduced oxygen atmosphere, often yielding vibrant, unique colors like copper red or celadon.

- Common Uses: High-fire, gas, or wood-fired ceramics.

Oxidation Glazes

- Characteristics: Fired in a kiln with plenty of oxygen, producing bright, predictable colors.

- Common Uses: Electric kiln firings; functional and decorative ware.

Satin Matte Glaze

- Characteristics: Combines the softness of matte with a subtle sheen, resulting in a silky finish.

- Common Uses: Functional pottery and contemporary designs.

Peacock Glaze

- Characteristics: Creates iridescent patterns and vibrant colors resembling peacock feathers.

- Common Uses: Decorative or high-impact sculptural ceramics.

Glaze Types (some)

Shino Glaze

Shino glazes originated in Japan during the 16th century and are known for their warm, earthy tones and unpredictable surface textures. Typically composed of feldspar, clay, and a small amount of ash, Shino glazes produce a wide range of effects, including orange, red, white, and black hues, depending on the firing conditions and application thickness. They are most often used in reduction firings at high temperatures, where the atmospheric conditions enhance their characteristic color variations. Shino glazes are valued for their rustic aesthetic, often featuring carbon trapping, which creates smoky patterns and enhances the organic appeal of the surface.

Shino glaze is often applied as the first layer in multi-layered glazing because of its unique properties and interactions with the clay body and other glazes. The phrase "Shino first or the worst" reflects the ceramic community’s understanding that applying Shino glaze on top of another glaze often leads to undesirable results. Here's why Shino needs to go first:

1. Proper Absorption and Adhesion

- Shino glazes require direct contact with the clay body to adhere properly and develop their characteristic effects, such as carbon trapping and flashing.

- If applied on top of another glaze, Shino can peel, crawl, or fail to stick because it cannot absorb into the clay. The base layer interrupts this essential process, making it critical to follow the mantra: "Shino first or the worst."

2. Enhancing Atmospheric Effects

- Shino is highly responsive to firing atmospheres, especially in reduction, where it produces its signature orange, smoky, or carbon-trapped effects.

- These effects are achieved through direct interaction with the clay body, which cannot occur if Shino is applied over another glaze. A top layer would block the Shino from showcasing its full range of atmospheric beauty.

3. Compatibility with Other Glazes

- Shino’s high alumina content and viscosity can create surface tension issues when applied as the top glaze, causing crawling or uneven textures.

- However, when Shino is applied first, subsequent layers of glaze can fuse with it during firing, creating rich, layered effects. Reversing this order often leads to unpredictable and less desirable results, hence the reminder: "Shino first or the worst."

4. Foundation for Layering

- Shino's earthy tones and thick textures make it an excellent foundation for layering other glazes. Applied first, it provides a stable base that can interact with additional layers in unique and appealing ways.

- If applied last, Shino’s thickness and tendency to resist flowing during firing often disrupt the underlying glaze, leading to patchy or messy results.

Conclusion

When using Shino glaze, always remember "Shino first or the worst." This approach ensures proper adhesion, maximizes atmospheric effects, and avoids technical issues like crawling or peeling. Shino’s beauty lies in its interaction with the clay body and its ability to complement other glazes when applied as the foundational layer.

Nuka Glaze

Nuka, meaning “rice bran” in Japanese, is a glaze traditionally made with wood ash and feldspar, creating a semi-transparent, glossy finish. The ash contributes natural fluxing properties, resulting in a fluid glaze that flows slightly during firing, leaving drips and pooling that add depth and character. Nuka glazes are typically applied over a dark clay body to highlight their milky white or blue-tinged appearance, which is accentuated in reduction firings. Their soft, flowing textures evoke a sense of movement, making them a popular choice for functional pottery and decorative ware alike.

Tenmoku Glaze

Tenmoku glazes, derived from Chinese ceramic traditions, are prized for their deep, glossy black or reddish-brown finishes. Rich in iron oxide, Tenmoku glazes produce a lustrous surface that often reveals subtle color variations, such as streaks of brown, gold, or red, depending on the firing atmosphere and clay body. They are typically fired at high temperatures in reduction kilns, where the iron oxide reacts to create their characteristic depth and warmth. The glaze often pools in textured areas, creating striking highlights and adding to its timeless appeal.

Celadon Glaze

Celadon is a transparent glaze with a delicate green or blue tint, historically associated with Chinese porcelain. It is achieved by adding small amounts of iron oxide to a glaze and firing it in a reduction atmosphere at high temperatures. The subtle, glassy finish of celadon enhances surface details, making it ideal for carved or textured pieces. Traditionally applied over white or light clay bodies, celadon is celebrated for its serene and elegant aesthetic, often reminiscent of jade.

Chun Glaze

Chun glazes, another legacy of Chinese ceramic tradition, are known for their opalescent, bluish tones and soft, fluid texture. They are typically formulated with high levels of silica and alumina, creating a thick, glossy surface that can exhibit streaks, drips, or pooling effects. Chun glazes are often applied over stoneware or porcelain and fired in reduction kilns, where variations in thickness enhance their unique interplay of blues and whites. The ethereal quality of Chun glazes makes them a popular choice for creating pieces with a luminous, almost otherworldly character.

Clear Glaze

Clear glaze is a transparent coating that enhances the underlying surface, whether it’s a bare clay body, slip decoration, or underglaze pattern. Available in glossy, satin, or matte finishes, clear glazes are versatile and can be used in both functional and decorative ceramics. The clarity of the glaze depends on the firing temperature and composition; over-application or improper firing may cause cloudiness or pinholing. A clear glaze is often used to protect and highlight intricate surface details, making it an essential choice for many potters.

Waxy Matte Glaze

Waxy matte glazes are characterized by their smooth, velvety texture and muted, soft appearance. Unlike glossy glazes, they do not reflect light, lending a quiet, understated quality to ceramic surfaces. Achieving a successful waxy matte finish often involves fine-tuning the balance of alumina and silica in the glaze recipe. These glazes are versatile, offering a tactile experience ideal for both functional ware and sculptural pieces, and are particularly effective at emphasizing the natural beauty of earthy tones or pastel colors.

Strontium Glaze

Strontium glazes incorporate strontium carbonate as a flux, which produces unique, vibrant color responses, particularly with certain oxides like copper or cobalt. They are often used in place of calcium carbonate (whiting) to achieve subtle differences in color and surface quality. Strontium glazes can range from glossy to matte finishes and are typically used in mid- to high-fire applications. Their ability to enhance bright, saturated hues makes them a favorite for creating dynamic, eye-catching ceramics.

Tea Dust Glaze

Tea dust glazes are known for their mottled surface, resembling fine specks of gold or green scattered over a dark, glossy base. This effect is achieved through the controlled crystallization of iron oxides during firing, often at high temperatures in reduction kilns. The glaze's depth and richness are heightened by the contrast between the dark background and shimmering specks. Tea dust glazes are frequently used for traditional forms like bowls and teapots, lending a sense of refinement and subtle luxury to functional pottery.

Oribe Glaze

Oribe glazes, named after the Japanese tea master Furuta Oribe, are renowned for their vibrant green hues and playful, asymmetrical patterns. The glaze typically contains copper as a colorant and is applied in thick, painterly layers. Firing in oxidation or reduction can create variations, from bright emerald greens to deeper, olive tones. Oribe glazes are often paired with contrasting white or brown areas on a piece, resulting in bold, dynamic compositions that reflect the aesthetic principles of the Momoyama period.