Demystifying Underglaze: Its Composition and Uses

Underglaze, a colorful addition to pottery, remains an enigmatic entity to many ceramic artists. This guide will shed light on the crucial elements of underglaze and provide insights on exploiting this versatile medium for an array of decorative and functional ware.

What Exactly is Underglaze?

Underglaze is a compound composed of flux material, metal oxide pigments, water, and binders. It's distinct from glaze in several ways:

• Underglaze fires at a lower temperature, approximately at cone 06.
• Underglaze adheres to raw or bisque clay unlike glaze, which forms a glassy coating.
• It offers translucent colors, as opposed to glaze's opacity.
• Rather than having a glossy finish like glaze, underglaze provides a matte texture.

These characteristics render underglaze perfect for introducing color while maintaining surface qualities.

Decoding the Ingredients and Chemistry of Underglaze

The concoction of underglaze encompasses the following elements:

• Flux: Ensures adhesion and durability. Commonly used fluxes include borax or low-temperature frit.
• Pigments: Metallic oxides that provide color. Examples include cobalt, copper, and chrome.
• Fillers: Substances like silica or alumina are added for texture and sheen.
• Binder: Components like gum or methyl cellulose are used to facilitate application.
• Water: Enhances fluidity and simplifies application.

During firing, these ingredients coalesce, allowing the colors to penetrate the clay body.

Comparing Underglaze and Glaze

While both glaze and underglaze are used to color clay, they exhibit distinctive traits:

Underglaze

• Fires at lower temperatures
• Offers translucent color
• Provides a matte finish
• Surface remains porous and absorbent
• Adheres to the clay surface

Glaze

• Requires higher firing temperatures
• Delivers opaque, solid color
• Offers a glossy or textured finish
• Forms a glass-like, non-porous surface
• Fuses with the clay surface

The Diverse Types of Underglaze

Underglaze is available in several forms, including:

• Liquid: This form presents vibrant fluid colors in containers, suitable for brushing and spraying.
• Pencils: Colored wax sticks are ideal for sketching fine details. The wax is eliminated during firing.
• Chalks: These dry blocks can be rubbed onto surfaces for a distinct effect.
• Slips: Highly fluid, slips are perfect for dipping, trailing, and pouring.

Leveraging the Versatility of Underglaze

Underglaze has become a staple in the potter's toolkit due to its flexibility. Its various uses include:

• Adding precise color to leather-hard clay
• Creating vibrant designs on bisque before glazing
• Executing dramatic over-glaze brushwork
• Developing crisp, customizable decals
• Utilizing the Mishima or inlay techniques to highlight carved areas
• Layering colors and textures under glazes
• Crafting special effects like lace drapes or resist patterns

With its wide range of colors and forms, underglaze catalyzes creativity.

In summary, underglaze offers a vibrant and adaptable coloring solution while preserving the clay surface's unique character. Unlike glaze, which can obscure underlying textures, underglaze enhances without concealing, providing potters with a powerful tool for creative expression.

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