Glazing is the part of making where the work can still go wrong after everything else has gone right. The pot survived the throwing, the drying and the bisque, and then it spends a few minutes under a brush and comes out of the kiln patchy, or crawled, or stuck to the shelf.
Most of that comes down to how much glaze went on and how evenly. This is the sequence I use and teach, written for brush-on glazes because that is what we make and what most people are working with at home. Dipping, pouring, sponging and spraying are here too, because at some point you will want them.
What is a glaze in ceramics?
A glaze is a thin layer of glass fused to the surface of a fired clay body. It is made from powdered minerals suspended in water, and it only becomes glass in the kiln, when the heat melts it and it cools into a solid skin.
That is the whole mechanism, and it explains most of what follows. For the ingredients and how the melt actually works, I have written that up separately in What Is a Ceramic Glaze.
What do you use to glaze ceramics?
Less than people expect. A working set is:
A soft brush with some body to it. Flat or round, wide enough to cross the surface in one pass. A thin watercolour brush will fight you. Keep a separate brush per colour, or at least per colour family, because glaze is almost impossible to wash out completely and a trace of a dark glaze will show up in a white one.
A banding wheel. It lets you keep the brush still and turn the pot, which is how you get an even band rather than a wobble. It makes more difference to an even coat than a better brush does.
A sponge. For wiping dust off the bisque, for cleaning the foot, and for applying glaze in its own right. A natural sponge gives the most even result.
Wax resist, if you want a clean foot without wiping.
A bucket or bowl large enough to submerge the piece, if you are dipping.
Everything else is optional. We stock the brushes, sponges and wax at the shop in Peckham, and there is a broader guide to where to find supplies in London here.
Before you start: the surface
Bisque that has been sitting on a shelf collects dust, and glaze does not grip dust. It is not the usual reason a pot disappoints, but it is the reason for a specific fault: bare patches and crawling where the glaze pulled back from a dirty spot.
Wipe the piece with a damp sponge. Not wetting the piece, just taking the dust off. Then let it dry before you glaze.
Fingerprints do the same thing. Skin oil resists glaze in the way wax does, so handle clean bisque by the foot or the rim rather than the belly.
How do you glaze ceramics at home?
The sequence, start to finish:
- Wipe the bisque with a damp sponge and let it dry.
- Shake the jar for about a minute, then stir. Brush-on glazes hold their suspension with gums, and those need waking up. A glaze that feels gritty or watery has not been mixed enough.
- Wax the foot, or plan to wipe it at the end.
- Apply the first coat. Load the brush properly and work in one direction across the whole piece. Do not go back over a stroke that is already drying.
- Let it dry until it loses its sheen and looks matt and chalky. How long depends on the humidity in the room and the thickness of the pot.
- Apply the next coat at ninety degrees to the first.
- Keep alternating direction for any further coats.
- Check the foot. Wipe it clean, or peel the wax.
- Let the piece dry completely before it goes anywhere near a kiln.
Brushing, dipping, pouring, sponging and spraying
Brushing gives the most control and uses the least glaze. You can put one glaze inside and another outside without a second bucket. It is slower, and it shows your hand, which is either the point or the problem depending on what you are making.
Dipping is fastest and gives the most even coat. It needs a bucket of glaze deep enough to submerge the piece, which means mixing litres rather than millilitres. Worth it for a run of the same form, not for one mug.
Pouring is how you glaze the inside of a narrow form. Fill it, swill it, pour it out in one movement. Hesitate and you get a thick ridge where the glaze pooled.
Sponging sits between brushing and dipping. A damp natural sponge loaded with glaze lays down a flatter, more even film than a brush does, with no stroke direction in it, and it is forgiving on curved and uneven surfaces. It is also how you get a broken, mottled surface on purpose: dabbing rather than wiping leaves a textured deposit that fires very differently from a smooth coat. Keep a separate sponge per glaze.
Spraying gives the most even coat of all and the softest gradients. It needs a compressor and a spray booth that extracts. Glaze dust in the lungs is the reason for the booth, not a nicety.
For brush technique in detail, see How to Apply Brush-On Glaze Evenly, Without Streaks.
How many coats, and how thick
Three coats in alternating directions is the starting point, not the rule. Vertical, horizontal, vertical.
The reason for alternating is that one pass of a brush is never as even as it looks while it is wet. Thin spots show in the fired piece as window-paning, faint stripes where the clay reads through. A coat at ninety degrees covers what the one underneath missed.
How many coats you actually want depends on the glaze.
- Some functional glazes are doing what they should at two coats, and a third only makes them more likely to run.
- Textured and sculptural glazes often need four, sometimes more. The lava glazes break open because of the thickness. Put them on thin and you get a flat, slightly odd colour instead of a crust. Crawl is the same: the beading is a thickness effect.
- Layering changes the arithmetic again. Two glazes at three coats each is six coats of material on the pot, which is enough to run on a vertical wall even when neither glaze would run alone. When you layer, take the coats down rather than up until you know how the pair behaves.
Thickness changes the result, not only the coverage. Applied thicker, most glazes go more opaque, more saturated and glossier. Applied thin, the same glaze can go translucent or matt and look like a different product. Golden reads as a warm honey-brown thin and lifts to a speckled gold built up. Snow Drift is more transparent thin and breaks into rivulets as it thickens.
Reactive glazes are more sensitive to this than flat colours. The lava range is covered in the lava guide, and for putting one glaze over another there are tested combinations in the layering guide. Start with the more stable glaze underneath and the more reactive one on top, then test the reverse.
The foot, the wax and the kiln shelf
Glaze melts. Anything glazed that touches the shelf fuses to it, and getting a pot off a shelf with a chisel usually costs you the pot as well as the shelf.
So the foot ring and the bottom centimetre of the wall stay bare. Two ways to get there:
Wax resist painted on the foot before you glaze. The glaze beads off it. Ordinary wax resist stays on and burns away in the firing. The one we stock is a removable wax, painted on the same way but peeled off before the piece is fired, which means you can correct a line that went wrong instead of living with it, and you can use it in a shared studio that does not allow wax resist in its kilns. It dries in five to ten minutes and goes darker as it sets, so you can see when it is ready. Peel it off fully before firing.
Wiping the foot with a damp sponge after glazing. Slower and less precise, but it needs no materials and you can see exactly what you are removing.
Either way, run your fingers over the foot before the piece goes in. A glaze crumb you cannot see is enough to stick it down.
Can I glaze ceramics without a kiln?
No. Glaze is glass, and glass needs kiln temperatures to form. Nothing that dries at room temperature is a glaze, whatever the label says.
What you can do without a kiln is paint a bisque pot. Acrylic, varnish, and the products sold as cold glaze or cold enamel are all paint. Some of them look convincing in a photograph. They sit on the surface rather than fusing to it, they wear and scratch, and they are not suitable for anything that holds food or drink.
If you have no kiln, use someone else's. We fire other people's work at the Peckham studio, and there is a guide to the options across the city in Where to Fire Your Pottery in London. If you are firing your own and want to understand what the schedule is doing, start with Electric Kiln Firing: Cones, Ramps and Slow Cooling.
Fire to the range given on the jar. Our glazes are cone 6 to 8. A glaze fired short of its range stays dry and underfused. A glaze fired past it runs.
What goes wrong, and what it looks like
Running. Glaze slides down the pot and pools at the foot, or welds it to the shelf. This is nearly always too much material. A thick coat puts more mass on a vertical surface, and once it melts, gravity has more to pull on, so it moves further before the kiln cools and sets it. Firing hotter than the glaze wants does the same thing by making the melt more fluid. Layered glazes are the common case, because the coats add up faster than people expect.
Bare patches and window-paning. Thin or missed coverage. A coat too few, or a brush that was not carrying enough glaze, or a pass that was not crossed by the next one.
Crawling. The glaze pulls back from the clay in the kiln and leaves bare islands with thick rolled edges. This is the dust and fingerprint fault, and it is also what happens when a glaze goes on much too thick and cracks as it dries.
Pinholing. Small sharp craters in an otherwise smooth surface. Gas escaping through the glaze as it melts, and not healing over because the firing cooled too fast or the glaze was thin over a rough spot.
Test tiles are how you stop guessing. Three controlled tiles on the clay you actually use, labelled with the glaze, the number of coats and the firing, will tell you more than ten pots glazed by instinct. Keep them, because they were fired in your kiln on your clay and no chart can tell you that.
Test tiles from one layering run, fired together. The glazes are the same across the row. What changes is the clay underneath, and that is enough to change the colour, the break and the texture.
Where to go next
- How to Apply Brush-On Glaze Evenly, Without Streaks, for the brush technique in detail.
- The GLOST Glaze Layering Guide, for putting one glaze over another.
- Are Ceramic Glazes Food Safe?, for anything you intend to eat or drink from.
- Where to Learn Glaze Making in London, if you want to make the glaze as well as apply it.
