Slip clay is liquid clay: clay particles suspended in water, thick enough to coat a surface. In everyday studio language, "slip" covers three different materials that do three different jobs: joining slip for attaching pieces, decorating slip for color and texture, and casting slip for pouring into plaster molds. They look similar in a bucket, but they are mixed differently and used at different stages of drying.
This guide is research-based. We compared clay and glaze maker information, ceramic reference sources and published casting guides rather than testing in our own studio. Sources are listed at the end.
"Slip clay" has a second, older meaning. Glaze chemists use it for natural clays that melt into a glaze on their own. Digitalfire describes the original Albany Slip, mined near Albany, New York, as a clay that melted to a glossy dark brown glaze at cone 10 in reduction, and lists Alberta Slip as a modern substitute. This page is about slip as liquid clay; that kind of slip clay is a glaze material.
What is slip in ceramics?
Slip in ceramics is clay suspended in water. AMOCA's ceramic vocabulary defines it as finely ground clay particles mixed with water, used for joining two pieces of clay and for decorating, and Seattle Pottery Supply describes ceramic slip as usually about the consistency of heavy cream. So a slip for clay is liquid clay that does a job the solid clay cannot: glue, paint or pourable casting material.
For joining slip, the plain answer to "is slip just watered down clay?" is yes. For the other two kinds it is a bit more than that. Decorating slip is sieved smooth and often has stains, oxides or other materials added, and casting slip is a measured mix of clay, water and a deflocculant that pours with far less water than plain clay would need.
Where slip fits in the clay sequence
Slip is used early, while clay is still unfired and still shrinking:
- Plastic (wet): throwing slip forms naturally on the wheel; casting slip becomes a solid wall inside a mold.
- Leather hard: the main stage for joining slip and decorating slip. See leather hard clay.
- Bone dry: too late for most slip, which tends to flake off. See bone dry clay.
- Bisque: after the bisque firing, ordinary slip will not stick well, because the fired clay no longer shrinks.
- Glazed: glaze goes over slip-decorated bisque; see how to glaze pottery.
The reason slip belongs on greenware is shrinkage. Digitalfire explains that slip applied at leather hard dries and shrinks together with the clay body, so the two stay bonded. Put the same slip on bone dry clay or bisque and the slip shrinks while the surface under it does not, which leads to cracking and flaking.
What is slip used for in pottery?
- Joining: gluing handles, spouts, slab walls, coils and feet onto a piece.
- Decorating: adding color under or instead of glaze, by brushing, dipping, pouring or trailing.
- Texture: combing, finger-wiping or marbling a wet layer of slip.
- Inlay: filling carved or stamped lines with a contrasting slip (the mishima technique).
- Casting: pouring into plaster molds to make identical hollow forms.
- Repairs: filling small gaps and seams in damp greenware.
Joining slip vs decorating slip vs casting slip
| Type | Consistency | Made from | Goes on | Main use |
|---|---|---|---|---|
| Joining slip | Thick, like yogurt or soft paste | Same clay body as the piece, plus water | Soft to medium leather hard clay | Attaching parts |
| Decorating slip | Smooth, like heavy cream | Clay (often white) plus water, often with stains or oxides | Wet to leather hard clay | Color, trailing, dipping, inlay |
| Casting slip | Pourable, like buttermilk, but dense | Clay powder, water and a deflocculant | Poured into plaster molds | Slip casting |
Joining slip
Joining slip is the glue of hand-building and of handles on thrown pots. Make it from the same clay body as the piece, so it shrinks and fires the same way. It should be thick enough to sit on a scored surface without running, roughly the texture of thick yogurt.
The method is the familiar score-and-slip: roughen both surfaces, brush on slip, press the parts together with a little wiggle and smooth the seam. Our scoring and slip guide covers the technique in depth, and hand-building pottery explains how joins fit into building coil and slab pieces. Some potters use "magic water" (water with a small amount of sodium silicate added) instead of slip; if you try it, follow a tested recipe and the supplier's handling directions.
Decorating slip
Decorating slip is a smooth slip, often made from a white or light clay, colored with commercial ceramic stains or metal oxides. It goes on wet or leather hard clay so it shrinks with the body. Common ways to apply it:
- Brushing: two or three coats for an even color.
- Dipping and pouring: a full coat over a leather hard pot.
- Slip trailing: squeezing lines and dots of slip from a bulb or bottle. See our slip trailing guide.
- Sgraffito and mishima: scratching through a slip layer, or inlaying slip into carved lines.
Two practical rules matter more than the recipe. First, the slip has to fit your clay body: a slip that shrinks much more or less than the body will crack or peel. Second, it has to mature at the cone you fire to. Make test tiles before decorating a whole set of pots. Related surfaces include engobes (slips adjusted to behave partly like a glaze) and terra sigillata (an extra-fine slip that can be polished to a sheen).
Casting slip
Casting slip is made for pouring into plaster pottery molds. The plaster pulls water out of the slip, a wall of clay builds up against the mold, and the extra slip is poured out. The trick is getting a slip that pours easily but contains as little water as possible, so the cast dries fast and shrinks less.
That is what a deflocculant does. Digitalfire explains that deflocculants such as sodium silicate or Darvan, added in small amounts, turn a thick slurry into a thin, pourable one with far less water. Its example uses about 30% water, where a plain clay and water slip would need more than 50% to pour.
Sources give slightly different targets for casting slip density (specific gravity, the weight compared with the same volume of water). Digitalfire says commercial casting slips usually fall between 1.7 and 1.8. A Ceramic Arts Network guide aims for 1.80 to 1.85 for most casting, from as low as 1.74 for volumetric casting up to 1.90 for casting flat slabs. Check the specific gravity your mold or slip supplier recommends.
To check specific gravity, Ceramic Arts Network suggests weighing 100 ml of slip in grams and dividing by 100. Add deflocculant a few drops at a time; their guide warns that too much makes casts slow to release and leaves soft spots. For a first try, a ready-made casting slip matched to your kiln's cone is simpler than converting your own clay.
Which clay is used for slip casting?
Most casting is done with clay bodies made for it rather than ordinary throwing clay. US suppliers sell ready-mixed casting slips in the same three families as moist clay: low-fire earthenware, mid-fire stoneware and porcelain. The Ceramic Shop, for example, lists Standard Clay casting slips rated cone 06 to 04 (terracotta), cone 4 to 6 (white stoneware) and cone 6 to 8 (porcelain), and Seattle Pottery Supply sells a white low-fire earthenware casting slip rated cone 06 to 04. Digitalfire adds that casting does not suit grogged bodies, because the grog does not stay suspended in the slip. The full process, from mold to finished cast, is in our slip casting guide.
The downsides of slip casting
Slip casting makes repeatable pieces, but it has real costs for a home potter. You need plaster molds, which are heavy and take time to make or buy. Digitalfire notes that casts in traditional plaster molds can take hours to release, and molds need to dry out between uses. The slip itself needs control: the right specific gravity and the right amount of deflocculant, which Digitalfire calls a fragile balance that changes with your clay mix and water. Seams from the mold have to be cleaned off each piece, and wide flat forms such as plates are hard to cast without tearing or warping.
Throwing slip and reclaim slurry are not casting slip. Without a deflocculant they hold too much water and will soak a plaster mold, crack as they dry and shrink heavily.
How to make slip from scraps
Joining and decorating slip are easy to make from trimmings and failed pieces of the same clay:
- Let the scraps dry completely. Bone dry clay slakes down faster and smoother than damp lumps.
- Break them into small pieces, gently and over a tub, to avoid dust.
- Put them in a lidded container and cover with water by an inch or so.
- Leave them overnight or for a day to slake into soft mud.
- Pour off excess clear water, then mix with a whisk, a hand blender kept only for clay, or a paint mixer on a drill.
- For decorating slip, push it through a sieve to remove lumps and grit.
- Adjust: add water to thin it, or leave the lid off for a day to thicken it.
- Label the container with the clay body and date.
Keep a small jar of joining slip for each clay body you use. Mixing a stoneware slip into a porcelain or low-fire piece is a common cause of failed joins.
Slip vs slurry
There is no strict technical line between the two words. Digitalfire uses "slurry" broadly for any water-based mix of insoluble clay and mineral powders, which includes slip and glaze. In studios, "slurry" usually means the rough, lumpy mix of clay and water that builds up while throwing or in a reclaim bucket, while "slip" means a smoother, mixed liquid clay with a set purpose and thickness. The Pottery Wheel treats the two as interchangeable, with slurry at the thicker end.
In practice: throwing slurry can become joining slip once it is mixed smooth and thickened. It is not a decorating slip until it is sieved, and it is never a casting slip without a deflocculant.
Common slip mistakes
- Using slip made from a different clay body than the piece.
- Putting decorating slip on bone dry clay or bisque, then finding it peeling after firing.
- Applying slip too thick, so it cracks as it dries.
- Using too much water at a join, which softens the walls and weakens the seam.
- Pouring unconverted reclaim slurry into a plaster mold.
- Skipping test tiles for colored slips.
Safety with slip and dry scraps
Wet slip is not a dust hazard, but the dry scraps and spills it comes from are. Clay contains crystalline silica, which the CDC's NIOSH links to silicosis, lung cancer and other lung and kidney disease. Wipe up slip spills while they are wet, do not dry sweep dried slip, and clean with a wet mop, wet sponge or HEPA-filtered vacuum, the approach OSHA requires for silica in workplaces. If you mix slip from dry clay powder, stains or oxides, wear a NIOSH-approved respirator and follow the safety data sheet for each material, including deflocculants.
What you need
For slip work you need lidded containers, a sieve, a soft brush or two, a slip trailing bottle and a scoring tool. Our pottery tools guide covers the hand tools, and the best clay for pottery guide helps you pick a body, since your joining slip should come from the same clay.
Sources: Digitalfire Reference Library by Tony Hansen, glossary entries for leather hard, deflocculation and slurry, and material entry for Albany Slip; Ceramic Arts Network, "How to Transform Your Clay Body into a Casting Slip"; The Pottery Wheel, "What is Slip in Pottery?"; Seattle Pottery Supply, "What is Greenware?", pottery glossary (slip, slip casting) and SP375 Lowfire Xtra White casting slip listing; Digitalfire glossary entries for slip casting and casting slip (plaster molds, grog, deflocculation); The Ceramic Shop casting slip listings (Standard Clay cone ranges); AMOCA Ceramic Vocabulary; CDC NIOSH crystalline silica topic page; OSHA 29 CFR 1910.1053(h) housekeeping. Specs checked October 2026.