Bottles of underglaze and bottles of glaze often sit side by side on the same studio shelf, with similar labels and similar jars. Painted onto raw pottery, they can even look alike. After the kiln, though, they behave very differently: one stays exactly where you put it, the other melts, flows and turns to glass. Knowing which is which decides whether your design comes out crisp, glossy, blurred or unexpectedly bare.
Quick answer: Glaze vs underglaze comes down to melting. Underglaze is a pigment-rich colored clay coating that does not melt into glass, so it holds fine detail and stays matte; it is applied to greenware or bisque and usually covered with clear glaze. Glaze is a glass-forming coating that melts in the kiln into a smooth, sealed surface, often glossy, that can move and blend. Use underglaze for painted designs and glaze for the final protective, decorative glass layer.
What Is Underglaze?
Underglaze is essentially a finely ground colored clay body, similar to a colored slip, loaded with stain or pigment. It contains little or none of the fluxes that make glass melt. Because it does not become fluid in the kiln, it stays exactly where you paint it.
Key characteristics:
- Stable during firing: lines and brushstrokes do not blur or run.
- Predictable color: what you see when painting is fairly close to the fired color, though colors usually intensify and can shift slightly.
- Matte or satin surface: when left unglazed, underglaze typically fires dry and matte.
- Applied early: often painted on leather-hard or bone-dry greenware, or on bisqueware.
- Usually covered: a clear glaze is commonly applied over underglaze to add gloss, depth and a sealed surface.
Underglaze also comes in pencils, crayons, chalks and transfer sheets, which makes it the go-to material for drawing and illustration on ceramics. Glaze is the companion layer that goes over it, and our roundup of ceramic craft glazes explains which clear and colored options pair well with underglaze work.
What Is Glaze?
Glaze is a mixture of materials, mainly silica (the glass former), fluxes (which lower the melting point) and alumina (which stiffens the melt), plus colorants or stains. In the kiln, it melts into a thin layer of glass that bonds to the clay body.
Key characteristics:
- Melts and flows: it can move during firing, sometimes running down vertical walls.
- Sealed surface: properly formulated and fired glaze creates a non-porous coating. Whether a glaze is food-safe depends on its formulation and firing, so always check the label.
- Wide range of finishes: glossy, satin, matte, crackle, crystalline, reactive and more.
- Color transformation: many glazes look nothing like their fired color in the jar.
- Applied to bisque: glazes are typically applied to bisque-fired ware, which is porous enough to absorb them.
Glaze vs Underglaze: Side-by-Side
| Feature | Underglaze | Glaze |
|---|---|---|
| Main purpose | Color and design | Protective, decorative glass surface |
| Melts into glass? | No (or very little) | Yes |
| Movement in firing | Minimal | Can move, blend and run |
| Detail retention | Excellent | Varies; fine detail can blur |
| Typical surface | Matte or satin | Glossy, satin or matte |
| When applied | Greenware or bisque | Usually bisque |
| Needs clear coat? | Often, for shine and sealing | No; it is the top coat |
| Color predictability | High | Lower; depends on thickness, clay and kiln |
| Typical application | Painting, drawing, stenciling, sgraffito | Dipping, pouring, brushing, spraying |
| Food surfaces | Not food-safe on its own; cover with a food-safe clear glaze | Food-safe only if labeled and fired correctly |
Why Underglaze Stays Put and Glaze Moves
The difference comes from chemistry. Glass needs a flux to melt at kiln temperatures. Glazes are formulated with enough flux to melt fully at their rated cone, so they become a viscous liquid that settles, flows and fills the surface. Underglazes are designed with little flux, so they sinter (bond particles together) without becoming liquid. That is why an underglaze line painted at 1 mm wide is still about 1 mm wide after firing, while a glaze line of the same width may soften or spread.
This also explains why glazes can pool in recesses and break over edges, revealing the clay or underlying color. That “breaking” is prized in many glazes but makes them less suitable for precise illustration.
How to Use Underglaze
- Choose the stage. Leather-hard or bone-dry greenware gives the strongest bond and allows sgraffito (scratching through the color). Bisque is easier to handle and less fragile.
- Clean the surface. Wipe dust off with a damp sponge. Dust can cause underglaze to flake.
- Apply in coats. For solid color, brush on two to three coats, letting each dry until it loses its shine. Alternate brush direction for even coverage. For watercolor-style washes, thin with water and apply one coat.
- Add details. Use fine brushes, underglaze pencils or slip trailers for lines and patterns.
- Fire. If applied to greenware, the pot is bisque-fired with the underglaze. If applied to bisque, some potters do a second low bisque firing to set it before glazing, which reduces smearing.
- Apply clear glaze. Dip, pour or brush a clear glaze over the design. Brush application over unfired underglaze can smear; dipping or a quick first coat helps.
- Glaze fire to the temperature recommended for the clear glaze and clay body.
How to Use Glaze
The general workflow for applying glaze to bisque:
- Clean the bisque. Wipe with a damp sponge to remove dust and oils. Avoid handling with lotion-covered hands.
- Wax the foot. Apply wax resist to the bottom and lower edge so glaze does not fuse the pot to the kiln shelf.
- Stir thoroughly. Glaze materials settle. Mix until smooth with no sediment at the bottom.
- Apply. Brushing: typically two to three coats, each dry before the next. Dipping: a few seconds in the bucket, depending on glaze thickness and bisque porosity. Pouring: for interiors and large surfaces.
- Check thickness. Too thin looks dry and patchy; too thick can crawl, pinhole or run.
- Clean the foot. Wipe any glaze off waxed areas with a damp sponge.
- Fire to the cone specified on the glaze label.
How to Use Glaze When Painting Designs on Pottery
If you want a painted look with glaze rather than underglaze, a few strategies help:
- Choose stable or “non-moving” glazes designed for brushwork.
- Keep decorated areas away from the lower part of vertical forms, where runs collect.
- Apply glaze over glaze cautiously; layering can create beautiful effects but increases running risk. Always test.
- Consider majolica, a technique where colored stains or glazes are painted onto an unfired opaque white glaze, giving a painterly look with relatively good stability.
Using Underglaze and Glaze Together
Most decorated pottery uses both. The classic sequence:
- Underglaze design on greenware or bisque.
- Bisque fire (if not already bisqued).
- Clear glaze over everything.
- Glaze fire.
Variations include painting underglaze only on some areas and colored glaze elsewhere, or leaving some underglaze unglazed for a matte contrast. Unglazed areas will not be sealed, so keep them off food-contact surfaces and away from rims.
Firing Temperatures and Compatibility
Both materials are rated for certain firing ranges, expressed in cones. Low-fire work is often around cone 06 to 04; mid-fire around cone 5 to 6; high-fire around cone 9 to 10. Many commercial underglazes are rated for a wide range, but some colors fade, burn out or shift at higher temperatures. Glazes are typically formulated for a narrower range.
Always check the label for both products and the clay body, and fire to the lowest common range that suits all three. When in doubt, test tiles are your best tool.
Non-Fired “Glazes” and Ceramic Paints
Some craft products are sold as ceramic paints or non-fired glazes. These are usually acrylic or enamel-type paints that air-dry or bake in a home oven. They can look glossy but are not true glass glazes, are generally not suitable for food-contact surfaces, and are less durable than fired glaze. They are useful for decorative pieces when you do not have kiln access.
How to Make a Useful Test Tile
Test tiles save pots. A good tile tells you how a combination looks on your clay, at your thickness, in your kiln.
- Make small L-shaped tiles from the same clay body you use for real work. The vertical part shows whether glaze runs; the flat part shows pooling.
- Press a texture into part of each tile so you can see how glaze breaks over edges.
- Paint stripes of underglaze in one, two and three coats.
- Bisque fire, then dip half the tile in clear glaze and leave half bare.
- On a second tile, apply colored glaze in one, two and three coats, overlapping a second glaze across part of it.
- Write the materials, coats and cone on the back with underglaze pencil or iron oxide before firing.
Keep fired tiles on a board or ring. Over time they become your most reliable color chart.
Troubleshooting Glaze and Underglaze Problems
| Problem | Likely cause | What to try |
|---|---|---|
| Underglaze flaking off | Dusty or oily surface, or applied too thick on bisque | Clean surface, thinner coats, apply on greenware |
| Smeared underglaze design | Clear glaze brushed over unfired underglaze | Dip or pour clear, or bisque the underglaze first |
| Cloudy clear glaze over color | Clear applied too thick or underfired | Thinner application, check cone and kiln |
| Crawling (glaze pulls into beads) | Dust, oils or very thick application | Clean bisque, thinner coats |
| Runs onto the shelf | Glaze too thick near the base, or overfired | Leave a bare band above the foot, check firing |
| Pinholes | Gases escaping, thick glaze, dusty bisque | Clean bisque, adjust thickness, slower firing |
Common Mistakes
- Brushing clear glaze vigorously over unfired underglaze: smears the design. Dip or pour, or bisque the underglaze first.
- Applying glaze too thick: causes runs, crawling and pinholes.
- Assuming underglaze is food-safe uncovered: cover functional surfaces with a food-safe clear glaze.
- Skipping test tiles: color and surface vary with clay body, thickness and kiln.
- Using high-fire temperatures with low-fire underglaze colors: colors may fade or burn out.
- Dusty bisque: leads to flaking and crawling.
Tips by Experience Level
First-time potters and paint-your-own-pottery visitors: stick to underglaze for designs and let the studio apply clear glaze. It is the most predictable route to a crisp result. Home studio hobbyists: build a small palette of underglazes plus one reliable clear glaze and one or two colored glazes rated for your kiln, then test combinations before mixing them on real pieces. Experienced makers: explore layering reactive glazes over underglaze accents, sgraffito through underglaze on leather-hard clay, and majolica-style painting on opaque glaze bases.
Which Should You Use?
- Detailed illustrations, lettering, patterns: underglaze, then clear glaze.
- Solid color with depth and gloss: colored glaze.
- Reactive, flowing, variegated surfaces: glaze, especially layered or reactive types.
- Matte, velvety painted surfaces on decorative work: underglaze left unglazed.
- Functional ware: food-safe glaze on all food-contact surfaces.
FAQs
What is the main difference between glaze and underglaze?
Underglaze is a colored coating that does not melt into glass and holds detail. Glaze melts into a glassy layer that seals the surface and can flow during firing.
Do you have to put clear glaze over underglaze?
Not always. Underglaze can be left matte on decorative pieces, but a clear glaze is needed for gloss and for sealing functional or food-contact surfaces.
Can you put underglaze over glaze?
Some underglazes can be applied over unfired glaze in majolica-style techniques, but results vary and colors may move. Test first.
Can you apply underglaze on bisque?
Yes. Underglaze works on bisqueware. Some potters do a quick bisque firing afterward to set it before clear glazing.
How to use glaze for beginners?
Clean bisque, wax the foot, stir the glaze well, apply two to three even brushed coats or a quick dip, wipe the foot clean and fire to the labeled cone.
Is underglaze food-safe?
Underglaze on its own is not intended as a food-contact surface. Cover it with a food-safe clear glaze for functional ware.
Final Thoughts
Think of underglaze as the drawing and glaze as the glass that protects and finishes it. Use underglaze for precise color and design, and glaze for sealing, shine and fluid effects, testing every new combination on a tile first. For product picks that suit hobby kilns and craft projects, see our top glaze picks for ceramic crafts in 2026.
