Underglaze is a ceramic color for decorating pottery, made mostly of clay, a small amount of flux and a high load of ceramic stain. You brush, sponge, draw or print it onto wet clay, greenware or bisque, and when the piece is fired the color stays exactly where you painted it. That is the key idea behind what underglaze is in ceramics: it behaves like colored clay, not like melting glass, so lines stay sharp.
This guide is research-based, using maker pages from AMACO, Mayco and Speedball and the Digitalfire ceramic reference. Specs checked October 2026.
What underglaze is made of
Digitalfire describes underglazes as "heavily pigmented ceramic compounds, normally applied by brushwork." A typical recipe holds clay, a flux such as feldspar, a high percentage of ceramic stain for strong color, and a gum such as CMC so it brushes smoothly. The stain is what gives the color; the clay makes it stick to the pot; the small amount of flux helps it bond in the kiln.
Because underglaze has so little glass-forming material, it sinters rather than melts. Digitalfire notes that underglazes sinter during the bisque firing and bond to the surface mechanically. In plain terms, it hardens and grips the clay but does not turn into a runny liquid, which is why it will not blur.
Is underglaze just colored slip? It is close. Slip is clay and water, sometimes with oxide. Underglaze is a refined, heavily stained relative made for bright, opaque color, while slips and engobes are usually thicker and used to change the surface of the clay body itself. Our clay slip page explains slip.
Underglaze, slip, engobe and stain
These four terms get mixed up, so here is the short version.
| Material | What it is | Main use |
|---|---|---|
| Underglaze | Clay, a little flux, a lot of stain, plus gum | Bright, opaque painted designs |
| Slip | Clay and water, sometimes with oxide | Joining, slip trailing, surface color |
| Engobe | A slip adjusted to fit the clay body | Covering a body with a different color |
| Stain | Raw ceramic pigment powder | An ingredient, not a finished color |
Digitalfire warns that stain powders used on their own either bleed into the glaze or stay unmelted, which is why stains are blended into underglazes, slips and glazes rather than painted on straight.
How underglaze differs from glaze
Glaze is mostly glass formers and flux. It melts into a glassy coat, can run, and makes a surface smooth and sealed. Underglaze is mostly clay and color. It stays put and fires matte unless you put clear glaze over it. Many pots use both: underglaze for the design, clear glaze on top. For the full side-by-side, including china paint and lusters, read underglaze vs overglaze.
What underglaze looks like after firing
On its own, fired underglaze is matte. AMACO calls the unglazed surface of its Velvet line "velvety smooth," and Mayco says its Fundamentals fire to "a soft, matte finish when left unglazed." Under a clear glaze the colors get deeper and glossy. Some colors also shift with temperature: dealer notes on AMACO Velvet describe V-382 Red as vivid crimson at cone 05, dark wine red at cone 5, and brownish by cone 10. That is why makers publish fired color charts by cone.
Opaque and translucent underglaze
Most jar underglazes are opaque: three coats hide the clay completely. Speedball, for example, calls its line "opaque underglazes" that "will not move or bleed." Translucent underglazes, such as Mayco's E-Z Stroke, are made to let the clay or lower layers show through, for shading and watercolor effects. Any opaque underglaze can also be thinned with water for a translucent wash, though the color will be lighter after firing.
The forms underglaze comes in
- Liquid jars: the most common form, such as AMACO Velvet, AMACO LUG, Mayco Fundamentals and Speedball. Brush or sponge on.
- Translucent underglazes: thinner colors for shading and watercolor looks, such as Mayco's E-Z Stroke line, which Mayco lists for brushwork, airbrushing and antiquing on greenware or bisque.
- Sprays: AMACO sells a Velvet Sprayz line for spraying.
- Semi-moist pans: AMACO's semi-moist underglazes work like a watercolor paint box.
- Pencils and chalk crayons: solid sticks for drawing on bisque. See underglaze pencils.
- Liners: squeeze bottles with fine tips, such as Mayco Designer Liner, for lines, dots and letters.
- Transfers: designs screen printed in underglaze onto paper, then pressed onto clay. See underglaze transfers.
Where underglaze fits in making a piece
Here is the usual order for a decorated mug made with underglaze:
- Throw or build the mug and trim it.
- Paint underglaze at leather hard, or wait and paint it after the bisque firing.
- Bisque fire. Underglaze on greenware sinters onto the clay in this firing.
- Cover the mug with a clear glaze labeled for your cone, keeping the foot clean.
- Glaze fire. The clear glaze melts over the underglaze and seals it.
Our bisque firing guide explains the first of those two firings.
When you apply it
Underglaze can go on at almost any stage before the glaze firing. AMACO lists Velvet for wet, leather-hard or bone-dry greenware and for bisque; Mayco says the same for Fundamentals, naming cone 04 bisque. Pencils and chalk crayons are made for bisque. Which stage is better depends on the technique, and our guide on how to use underglaze compares greenware and bisque in detail.
How hot underglaze is fired
Each line has a rated range. AMACO Velvet is rated cone 05 to cone 10, Mayco Fundamentals cone 06 to 10, Speedball cone 05 to 10, and Duncan Cover-Coat cone 06 to 6. On Orton's chart for self-supporting cones at 108°F per hour, cone 06 is 1,828°F (998°C), cone 6 is 2,232°F (1,222°C) and cone 10 is 2,345°F (1,285°C). Our pottery cone chart has the full table.
A short history
Underglaze painting is centuries old. Wikipedia traces it to China's Tang and Five Dynasties periods, and it became famous in Ming and Qing blue and white porcelain, painted with cobalt under a clear glaze. Cobalt was one of the few colors that survived the high firing that porcelain needed. In England, Staffordshire potters developed underglaze transfer printing from the 1760s. Modern commercial stains are what make today's wide underglaze palettes possible.
Underglaze and food safety
Makers tie food-surface use to clear glaze. AMACO says Velvet holds an approved food-safety status when fired under its LG-10, F-10 or HF-9 clear glazes, and Mayco says Fundamentals are dinnerware safe once clear glaze is applied. Speedball calls its underglazes "suitable for dinnerware when used and fired as directed."
Those statements depend on following the maker's directions and firing to the stated cone. Your clay, your clear glaze and your kiln all affect the result, so test functional ware. Read our food safe glaze guide before selling or gifting mugs and plates.
Can you make your own underglaze?
Yes. Potters mix their own from ceramic stain, a clay, a flux or frit, and a gum, which is the same recipe structure Digitalfire describes. It is a project for later: you have to balance the melt so the color neither bleeds nor flakes off, and you are handling dry powders. Most home potters start with commercial jars, which are tested across a cone range.
Common mistakes with underglaze
- Too few coats. Solid color usually takes about three coats; one coat looks streaky after firing.
- Brushing clear glaze hard over it. Unfired underglaze can smear; dip, spray or sponge the first clear coat.
- Ignoring the cone. Pinks, reds and yellows can fade near the top of their range.
- Treating it as finished before firing. Unfired underglaze rubs off and washes away.
- Underglaze on kiln shelves. Keep the bottom of the pot clean; our kiln wash page covers shelf protection.
Safety notes
Dried underglaze and clay dust contain silica. Wipe spills and scraps with a damp sponge, mop rather than sweep, and wear a NIOSH-approved respirator if you mix dry materials. Keep jars and brushes away from food areas, and read each label's safety seal.
What you need
To try underglaze, you need a few jars of color, soft brushes, bisque or greenware to paint, and a clear glaze for your cone. Our best underglazes guide compares the main brands by cone range and coverage.
Sources: Digitalfire glossary entry for underglaze; AMACO Velvet product sheet and AMACO shop underglaze pages; Mayco 2023 underglaze catalog and Fundamentals color guide; Speedball underglazes page; Duncan Cover-Coat page; Krueger Pottery Velvet listings; Orton cone temperature chart. Specs checked October 2026.