Raku clay is any clay body that can take the violent temperature swing of a raku firing without cracking. In raku, a bisqued pot is heated to roughly 1,470°F to 1,850°F (800°C to 1,010°C), lifted out glowing with tongs and dropped into a can of combustibles or left to cool in the open air. A normal smooth throwing clay often cracks under that treatment. A raku clay is built to flex with it.
This guide explains what makes a clay suitable for raku, how to judge a body you already own, and which raku clay bodies US potters can buy. It is research-based: we compared clay makers' published data and potters' references and did not run raku firings ourselves. The firing process itself is covered in our raku firing guide, and the kilns in our raku kiln guide.
Why raku is hard on clay
Every clay contains free silica (quartz). Quartz changes its crystal form at about 1,063°F (573°C), and in doing so it expands on heating and contracts on cooling. In a normal electric kiln firing this happens slowly and evenly through the wall. In raku it happens in seconds and unevenly: the outside of the pot cools much faster than the inside, and the rim cools faster than the base. Any body that is dense, tight and fine-grained has no room to absorb that stress, so it cracks, sometimes with a loud ping as the pot leaves the kiln.
That is the core requirement of a raku clay: thermal shock resistance. Everything else (texture, color, how it throws) comes second.
What makes a clay suitable for raku
Makers and potters describe the same handful of properties:
- An open body. Standard Clay describes its 239 Raku as an "open clay body specially formulated to withstand thermal shock". Open means there are coarse particles and small voids that let the body move without cracking.
- Grog, sand or both. Grog is clay that has already been fired and ground, so it does not shrink or change much in the kiln. Sand works in a similar way. Both break up the fine clay matrix and stop cracks from running. Our guide to grog in clay explains grog sizes and amounts.
- Kyanite in some bodies. Kyanite is a mineral that converts to mullite when heated, which adds strength and helps the body resist shock. Standard sells a raku body with kyanite and says the kyanite "adds strength".
- Low shrinkage at raku temperatures. Standard 239 shrinks about 8.0% at cone 04, and Standard 295 about 5.0% at cone 06. Lower shrinkage usually means less stress in the wall.
- Porosity left in the fired body. A raku body is not meant to vitrify. Standard 239 absorbs about 17.0% at cone 04. That porosity is part of why it survives, and it also lets smoke darken unglazed areas and crackle lines.
Form matters as much as the clay. Even walls, no thick bases, no trapped air pockets and rounded rather than sharp transitions all reduce cracking in any body.
Raku clay bodies compared
These are raku clay bodies sold to US potters. Figures are from the maker's own page; where the maker does not publish a figure, the table says so.
| Clay | Cone range | Shrinkage | Absorption | Opening material | Fired color |
|---|---|---|---|---|---|
| Standard 239 Raku | 04 to 10 | 8.0% at cone 04; 13.5% at cone 10 | 17.0% at cone 04; 3.0% at cone 10 | Sand | Not published by the maker |
| Standard 295 Raku Body with Kyanite | 06 | 5.0% | 7.4% | Kyanite | Not published by the maker |
| Laguna #250 Raku (WC-636) | Listed as "Raku" | Not published by the maker | Not published by the maker | Medium coarse texture; material not stated | Buff in oxidation |
Standard 239 Raku Clay
Standard 239 is one of the most widely stocked raku clays in the US, carried by dealers such as Blick and Chesapeake Ceramics. It is picked here because it covers both raku and ordinary glaze firings: Standard rates it from cone 04 to cone 10, and its cone 10 data (3.0% absorption) shows it becomes a dense stoneware when fired high. That lets you use one bag for raku and for cone 6 or cone 10 pots.
- Cone range: 04 to 10
- Shrinkage: about 8.0% at cone 04, 13.5% at cone 10
- Absorption: about 17.0% at cone 04, 3.0% at cone 10
- Contains: sand
- Size: 50 lb box
Pros
- Made for thermal shock
- One body for raku and high-fire work
- Stocked by several US dealers
Cons
- Sandy texture is rough on hands when throwing
- Fired color not published by the maker
Who should skip it: naked raku and burnishing work, where a smoother body is easier to polish.
Source conflict: Standard's own page gives 239 data at cone 04 and cone 10. Chesapeake Ceramics' listing gives cone 6 figures in its description (about 13% shrinkage and 4.5% absorption) but cone 10 figures in its spec list. Use Standard's numbers and test at your own cone.
Standard 295 Raku Body with Kyanite
Standard describes 295 simply: cone 06, good for large pieces, and the kyanite adds strength. Its 5.0% shrinkage is the lowest of the bodies here, which helps big forms survive.
- Cone: 06
- Shrinkage: 5.0%
- Absorption: 7.4%
- Contains: kyanite
Pros
- Very low shrinkage
- Maker recommends it for large pieces
- Kyanite for strength
Cons
- Rated only to cone 06, so not for stoneware glaze firings
- Fewer dealers list it than 239
Who should skip it: potters who want to use the same clay for raku and cone 6 work.
Laguna #250 Raku (WC-636)
Laguna describes #250 as a smoother version of its WC-635 Miller #200 Raku clay. It fires buff in oxidation and has a medium coarse texture. Laguna lists its shrinkage, absorption and expansion as N/A, so you will need to test it. When we checked in October 2026, Laguna's page showed it as sold out; Clay-King sells a 4 lb sample.
Can you use stoneware for raku?
Often, yes. Many potters raku fire a coarse, grogged stoneware they already use, and Standard 239 is itself rated to cone 10. The Pottery Wheel suggests that an ungrogged stoneware can be opened up with grog, giving about 30% grog as a rule of thumb. Fine, smooth throwing bodies are the riskiest choice. If you want to try your usual stoneware, start with small, evenly thrown test pieces and expect a few losses.
One thing to watch: a stoneware bisqued too hot becomes denser and less able to take shock. Keep raku pieces at an ordinary low bisque, around cone 06 to 04. Our bisque firing guide covers that step.
Can you use porcelain or earthenware for raku?
Porcelain: possible, but less forgiving. Porcelain is dense and fine, so it has the least room to absorb shock. Lucktaylor Ceramics, a UK raku potter, reports seeing slab-built porcelain survive raku, and The Pottery Wheel says fine grog and thin, even walls help. Many potters use a porcelain-like white body with added grog instead of pure porcelain.
Earthenware: low-fire red clays are open and porous, so they can survive raku, but The Pottery Wheel notes that their high iron content can work against the dark carbon effects many raku potters want. They also take on a brown cast that mutes bright raku glazes.
Clay color and raku effects
The body color shows through every raku glaze and carbon effect. Lucktaylor Ceramics notes that darker clays give darker, muted glaze tones, while lighter bodies give brighter color and stronger contrast with smoke. For crackle glazes, where black smoke lines on a white or pale glaze are the whole point, a light-firing body works best. For copper lusters, a darker body can deepen the color. The glazes themselves are covered in our raku glazes guide.
For naked raku and horsehair work, where the bare clay is the surface, potters prefer a smooth, light body that can be burnished. Heavily grogged raku clay is hard to polish. Lucktaylor's preferred body for naked raku is a smooth clay with enough fine grog for strength.
Throwing and hand-building with raku clay
- Expect texture. Sand and coarse grog are hard on hands and can scratch when you compress a rim. Some potters throw with a rib more than bare fingers.
- Hand-building suits it. Coarse raku bodies hold their shape for slabs, coils and large sculptural forms.
- Keep walls even. A thick base under a thin wall is the classic raku crack.
- Dry slowly and fully. Raku pots still go through a normal bisque, so they must be bone dry first.
- Store it sealed. Like any moist clay, keep bags tied to stop it drying out.
Why raku pots crack, and how to reduce it
- Clay too dense. Switch to an open raku body or a grogged stoneware.
- Uneven walls or thick bases. Trim the foot and keep walls consistent.
- Bisque too hot. A tighter bisque body handles shock less well.
- Pulling the pot before the glaze is mature, then cooling it in a draft. The outside shrinks while the inside is still hot. Follow the timing in your firing plan.
- Cold or wet tongs on a hot rim. Grip low on the body where the wall is thicker.
- Water quenching a pot that cannot take it. Quenching adds even more shock; save it for bodies and forms that have survived air cooling.
Safety notes
Raku involves open flame, propane and pots near 1,800°F (about 980°C). Follow your kiln maker's instructions, your local fire code and propane safety rules, fire outdoors away from buildings and overhangs, and wear heat-resistant gloves, a face shield and natural-fiber clothing. Never build or modify a burner yourself. Dry raku clay contains crystalline silica: wet clean and wear a NIOSH-approved respirator when sanding or mixing dry clay. Raku ware stays porous and is meant for decorative use; see our raku pottery guide.
What you need
Besides a bag of raku clay, you need an ordinary kiln for the bisque and a raku kiln with tongs and a reduction can for the firing itself. Our guide to the raku kiln compares gas and electric models and their setup needs.
Sources: Standard Clay product pages for 239 Raku and 295 Raku Body with Kyanite; Laguna Clay product page for #250 Raku (WC-636); Clay-King listing for the Laguna #250 sample; Chesapeake Ceramics and Blick listings for Standard 239; The Pottery Wheel, The Best Clay for Raku Pottery (quartz inversion, grog rule of thumb, porcelain and earthenware); Lucktaylor Ceramics, What's the Best Clay to Use for Raku (clay color, porcelain, naked raku). Raku temperature range as published on our raku firing guide. Specs checked October 2026.