Speedball Underglaze Chart: 48 Colours, Cones and Tips

How the Speedball underglaze chart works

The chart lists the 48 Speedball underglaze colour names that US pottery supplier M&N Clay publishes for the range, with item numbers for the 25 colours Stone Leaf Pottery lists by number, such as 1059 Turquoise and 1105 Lilac. Search matches names, numbers and colour groups, so “blue” finds Royal Blue, Sky Blue, Blue Frost and the rest.

Each colour has an approximate swatch suggested by its name. Underglaze names are usually literal, but the fired colour still depends on your clay, how thickly you paint, the cone you fire to and whether a clear glaze goes over the top. Treat the swatch as a label, and look at Speedball’s own fired chips and your test tiles for the real colour.

Pick a colour and the panel above shows its firing range and finish. The Print button gives you a clean list, handy for planning a class project or labelling bottles.

What firing range are Speedball underglazes?

Speedball underglazes are formulated to fire from cone 05 to cone 6, about 1021 to 1243 °C by Speedball’s figures, and Speedball says they’ve also been fired successfully to cone 10. That wide range makes them easy to use alongside both earthenware and mid-fire stoneware.

Colour can shift across that range. Some underglazes stay bright at low fire but soften or change at cone 6 and above, especially reds, pinks and some yellows. Speedball publishes a poster of fired chips at different cones, with and without clear glaze, which is the best way to see how each colour moves before you commit.

For bisque, Speedball’s FAQ suggests firing to cone 05 or 04 before applying its glazes and underglazes. Our firing service bisques at cone 06, which leaves ware slightly more porous. If your underglaze or clear behaves differently on our bisque, a test tile will show it.

How do you apply Speedball underglaze?

Paint underglaze onto greenware or bisque in two or three thin coats for solid colour, letting each coat dry before the next. One coat often looks streaky after firing, especially with lighter colours over darker clay.

Underglaze behaves more like paint than glaze. It doesn’t move much in the kiln, which is why it’s popular for detailed decoration, lettering and illustration. You can brush it, sponge it, trail it or use it with stencils and sgraffito, scratching through to the clay underneath. Our guide to sgraffito tools covers that technique.

Speedball notes that underglaze fires matte and isn’t sealed unless a clear glaze is applied over it. For anything that will hold food or drink, cover the underglaze with a suitable clear glaze and fire it to that glaze’s cone.

Underglaze vs glaze: what’s the difference?

Underglaze is a coloured clay slip with little or no glass-forming material, so it stays put and fires to a matte, colourful surface. Glaze is mostly glass-forming material that melts into a smooth coating. Underglaze is for colour and detail; glaze is for the surface.

That’s why the two are so often used together. Paint your design in underglaze, bisque or not as you prefer, then dip or brush a clear glaze over the top. The clear makes the colours deeper and glossier and seals the surface. Our article on the difference between glaze and underglaze goes into more detail.

Testing underglaze colours

A simple underglaze test tile has a stripe of each colour at one, two and three coats, with clear glaze over half of the tile. That shows you how coverage builds and how the clear changes each colour, all from one firing.

Make tiles from each clay you use, since a red earthenware changes underglaze colours far more than white stoneware. Label the back with the colour names, item numbers and cone. Kept together, a set of tiles becomes your own fired version of the chart.

If you don’t have a kiln, our kiln firing service in Mordialloc can fire your tiles at cone 03 for earthenware or cone 6 for mid-fire, both within Speedball’s range.

Common underglaze mistakes

The most common mistake is one thin coat, which can fire patchy. The second is leaving underglaze unsealed on pieces meant for food or drink. The third is choosing colours from a screen. Every monitor shows colour differently, so trust fired tiles over swatches, and look at your tiles in daylight as well as under studio lights.

Another is putting underglaze on too thickly on bisque, which can flake or crawl under a glaze. Several thin coats beat one heavy one. Finally, keep bottles closed between uses so they don’t thicken, and stir well, because heavy colourants settle to the bottom.

If an underglaze has thickened, add a little water and stir until it brushes smoothly again. Test the thinned colour before relying on it, since more water means less colour per coat, and you may need an extra coat to match your earlier tiles.

Planning a palette with the Speedball underglaze chart

With 48 colours to choose from, it helps to plan a small palette before you start painting. Pick a light, a mid and a dark from the same colour group, plus one accent, and you’ll have enough contrast for shading and detail without the piece looking busy. The colour filter in the chart makes it easy to see every blue or every green side by side.

Mixing underglazes is possible too, since they behave much like paint, but mixed colours don’t always fire the way they look wet. If you mix, make a test tile of the mixture before you rely on it, and write the proportions on the back.

For layered effects, paint the lightest colours first and the darkest last, letting each dry before the next. Outlines in black or a dark brown go on at the end. Many potters bisque fire a decorated piece before adding the clear glaze, so a smudge while glazing doesn’t spoil the design.

Finally, keep a printed copy of this chart beside your bottles. The print button gives you a clean list, and ticking off the colours you own makes it quick to see what you need before your next order.