Glazing is one of the most transformative stages in the pottery process — the moment where a raw, bisque-fired ceramic piece takes on its final colour, texture, and character. Understanding how glazes work, how to apply them, and how different kilns affect the result is essential to producing consistent, beautiful ceramics. For a full overview of the pottery process from start to finish, see How to Make Pottery: A Complete Step-by-Step Guide.
What Is a Glaze?
A ceramic glaze is a glassy coating applied to the surface of bisque-fired clay. When fired at high temperature, the glaze melts and fuses to the ceramic body, creating a smooth, waterproof surface. Glazes are made from a combination of silica (the glass-forming material), alumina (for stability), and flux (which lowers the melting point), along with metal oxides that produce colour.
The same glaze can produce very different results depending on the clay body, firing temperature, application thickness, and kiln atmosphere.
Types of Glaze
Matte glazes produce a soft, non-reflective surface with a tactile, velvety quality. They tend to show the texture of the clay body beneath and are well suited to organic, handcrafted forms. The Avoca white glaze used across the Polly Barton Ceramics wave and sculptural collections is a soft matte-satin finish — warm, timeless, and complementary to the ruffle and wave forms it covers.
Glossy glazes are highly reflective and glass-like. They are easy to clean and work well on functional tableware, though they can feel less artisanal on handcrafted pieces.
Satin glazes sit between matte and gloss — a subtle sheen that catches light without being reflective. Often the most versatile finish for contemporary homeware.
Reactive glazes contain materials that respond unpredictably to heat — producing movement, pooling, and variation across the surface. No two pieces fired with a reactive glaze are identical, making them particularly suited to handcrafted work.
Terracotta-compatible glazes must be formulated for lower firing temperatures. When used over terracotta clay, glazes can produce rich, earthy tones — deep ochres, warm browns, and burnt oranges — that complement the natural colour of the clay body.
Glaze Application Techniques
Dipping is the most efficient method for even, consistent coverage. The bisque-fired piece is submerged in a bucket of glaze and withdrawn in a single smooth motion. Dipping produces an even coat and is well suited to bowls, vases, and platters.
Pouring is used for larger pieces or the interior of forms that can't be easily dipped. Glaze is poured over or into the piece and allowed to drain, leaving an even coat.
Brushing allows for detailed, controlled application — useful for applying multiple glaze layers, creating patterns, or glazing specific areas. Brush marks can add texture and character to the finished surface.
Spraying produces the smoothest, most even coat and is ideal for achieving gradients and subtle colour transitions. It requires a spray booth and appropriate ventilation.
The thickness of glaze application significantly affects the final result. Too thin and the glaze may appear patchy or crawl during firing; too thick and it may run, pooling at the base of the piece and potentially fusing it to the kiln shelf.
Electric Kiln vs Gas Kiln — How the Kiln Affects Your Glaze
One of the most significant — and often overlooked — factors in glaze results is the type of kiln used for firing.
Electric kilns fire in an oxidation atmosphere. Oxygen is freely available throughout the firing, which means metal oxides in the glaze behave predictably. Colours tend to be clean and consistent — whites are bright, blues are true, and results are reliable and repeatable. Electric kilns are the most common choice for studio potters and are well suited to producing consistent results across a production range.
Gas kilns can be fired in either oxidation or reduction. In reduction firing, the kiln is starved of oxygen at key points during the firing cycle. The combustion gases — carbon monoxide and carbon dioxide — are forced to draw oxygen from the metal oxides in the glaze and clay body, fundamentally changing the chemistry of the surface. The results are often more complex and unpredictable: iron-bearing glazes shift from yellows and browns to rich greens and greys; copper glazes can produce deep reds; and the clay body itself takes on a warmer, more varied tone.
The same glaze recipe fired in an electric kiln and a gas kiln in reduction can produce dramatically different results — which is why glaze testing across different kiln types is essential when developing a new palette.
At Polly Barton Ceramics, the Avoca white glaze is developed and tested to perform consistently in an electric kiln, producing the soft, warm white finish that defines the wave and sculptural collections.
Glaze Firing Temperatures
Stoneware glazes typically fire between 1,200°C and 1,280°C (cone 6–10). At these temperatures the glaze becomes fully molten, flows slightly across the surface, and then sets as the kiln cools — producing a smooth, durable finish that is waterproof and food safe.
Earthenware and terracotta glazes fire at lower temperatures — typically 1,000°C to 1,100°C (cone 06–1). The lower firing temperature means the glaze and clay body are less fully fused, making earthenware more porous and less durable than stoneware, though no less beautiful.
Common Glazing Problems and How to Avoid Them
Crawling — the glaze pulls away from the surface during firing, leaving bare patches. Usually caused by glaze applied over a dusty surface, or glaze applied too thickly.
Running — the glaze becomes too fluid during firing and drips down the piece. Caused by glaze applied too thickly, or a glaze with too much flux for the firing temperature.
Pinholing — small holes in the glaze surface caused by gases escaping from the clay body during firing. Can be reduced by a slower firing schedule or a longer soak at peak temperature.
Colour inconsistency — variation in colour across a batch. Often caused by inconsistent application thickness or variation in kiln temperature across the chamber.
Polly Barton is a ceramicist who creates hand-built sculptural and functional works that explore themes of movement and flow. Browse the wave collection or the sculptural ceramic vases.