The Art of Raku Glazing: Techniques, Safety, and Stunning Effects

Raku is the one pottery process where the most exciting part happens after the kiln is switched off. You pull a glowing pot out at around 950°C, drop it into a bin of sawdust, and watch smoke curl over the rim while the glaze cracks and the colours shift in front of you. No other firing method delivers that kind of theatre from such modest equipment — a small kiln, a metal bin, a pair of long tongs. It also punishes carelessness faster than anything else in the studio. Get the reduction right and your crackle sings. Get the safety wrong and you will regret it.

What Raku Actually Is

Raku began in sixteenth-century Japan as a low-fired, lead-glazed tea-ware process, made for the tea ceremony. The western version studio potters use today is a different animal: pots are fired quickly to roughly 900–1000°C, then removed while still glowing and subjected to post-firing reduction.

The kiln is only half the story

Once the pot leaves the kiln, three things happen almost at once. The glaze solidifies and takes on whatever atmosphere surrounds it. Carbon from burning sawdust or newspaper gets trapped in the molten surface and in the cracks. And the sudden temperature drop — especially a water quench — shocks both glaze and clay body, which is what opens up the crackle. You are not just firing a glaze; you are staging a reaction.

Why the results are unpredictable

Every variable counts: how fast you fire, how thick the glaze is, how long the lid stays shut, how damp the sawdust is, how cold the air is on the day. Two pots from the same bucket will come out looking like distant cousins. There is no way to make raku fully repeatable, but there is plenty you can control.

Setting Up: Space, Kit and Clay

• A raku-capable kiln — electric, gas, or a small top-loading fibre kiln you can open hot without wrecking it.
• Long-handled tongs, a spare pair, and a heatproof board or trolley.
• A metal reduction bin with a tight lid, filled with sawdust, newspaper, straw or a mix.
• A metal quench bucket of water, if you plan to quench.
• Leather gauntlets, a thick apron, a face shield and a P3 respirator.
• Raku clay — a heavily grogged stoneware or crank body that can survive thermal shock.
• Low-temperature raku glazes, mixed wet, plus test tiles.

Work outside. Not in a shed with the door open; genuinely outside, on hard standing, well clear of fences, dry grass, bins and anything flammable. Raku smoke is thick and unpleasant, and neighbours may have opinions. Check whether your council has rules about smoke nuisance before you plan a firing afternoon.

The Glaze Palette That Works

Raku glazes are formulated for low temperatures, usually frit- or boron-based. They are not food-safe glazes and are not intended to be.

Crackle glazes

A white or clear crackle over a slip or terracotta body is the classic starting point. The cracks show because carbon from the reduction seeps into them, drawing dark lines across a pale surface. Thicker glaze gives bigger cracks. Oxides brushed under a clear crackle give colour that reads through the glaze.

Copper mattes and metallics

Copper glazes respond dramatically to reduction. Depending on atmosphere and cooling, you can get deep reds, oil-slick purples, coppery greens and metallic bronze surfaces. These reward patience with the lid and a slower, gentler reduction. Turquoises and blues with fine crackle are equally popular and rather more predictable.

The Raku Cycle, Step by Step

1. Bisque fire your work, glaze it, and let it dry completely.
2. Fire fast to around 900–1000°C, watching through the peephole until the glaze is glossy and molten.
3. Turn off the kiln. Put on every item of protective kit before you open anything.
4. Open the lid, stand upwind, and lift the pot with tongs. Move slowly — glowing pots are soft, and a dropped one is a real hazard.
5. Set the pot briefly on a heatproof surface, then place it into the reduction bin.
6. Cover it with sawdust or newspaper and shut the lid. Leave it ten to twenty minutes.
7. Quench in water or let it cool slowly in the bin. Quenching deepens crackle and freezes colours; slow cooling can give richer metallics.
8. Scour the cooled pot with water and a scouring pad to remove soot.

Coaxing Better Crackle

Crackle is a mismatch: the glaze contracts more than the clay as it cools, so it splits. You can influence it. Thicker glaze, faster cooling and a water quench all open the cracks further. A fine, even crackle usually comes from a thinner glaze and a gentler quench. Contrast matters more than the crackle itself — dark marks on a pale glaze read best. Bowl forms hold heat longer and often crackle more heavily than flat tiles, so test the shape you actually make.

Keep notes. Glaze name, thickness, firing time, reduction length, quench or slow cool, and a photograph of the result. After a dozen firings you will have your own reference file, far more useful than anyone else's recipe.

Safety, Without Compromise

Raku involves open flame, hot metal, smoke and glaze materials you should not breathe. None of it is difficult to manage; all of it punishes shortcuts.

• Fire outdoors, upwind of the kiln, away from anything combustible. Keep a fire extinguisher and a bucket of sand within reach.
• Wear leather gauntlets, a thick apron and a face shield for every kiln opening. Avoid synthetic clothing.
• Wear a P3 respirator and gloves when handling dry glaze materials, especially oxides. Mix glazes wet, and never dry-sweep glaze dust.
• Never eat, drink or smoke in the glazing area. Wash hands and forearms afterwards.
• If you fire with gas, check hoses and connections for leaks and follow the manufacturer's instructions exactly. Store cylinders outside.
• Carbon monoxide is odourless. Never reduce indoors or in a garage, and keep children and pets well away from the firing area.

Treat finished raku as decorative. The surfaces are crazed and porous, the glazes are not formulated for food contact, and sealing does not make a raku bowl safe for a stew. Use pieces for display, dried arrangements or as planters with a separate inner pot. If you want functional tableware, that is a different glaze and a different firing.

Your First Firing: Keep It Small

Start with a handful of test tiles and two or three small pots. Fire with someone who has done it before, even once, and watch the whole cycle before you take charge. Choose a still, dry day. Set out the bin, the tongs, the quench bucket and your protective kit before the kiln goes on, so nothing is a scramble when the glaze is molten. Then fire, look after the basics, and let the smoke do the interesting part.

Photo: IlonaBurschl / Pixabay