Slip casting is a way of making pottery by pouring liquid clay, called casting slip, into a plaster mold. The plaster soaks water out of the slip, a layer of clay builds up against the mold wall, and after a set time you pour out the extra slip. When the cast firms up, you open the mold, clean the seams and dry, bisque and glaze fire the piece like any other pot. Factories use it for sanitaryware, figurines and teapots; at home it is the easiest way to make a set of identical mugs or vases.
This guide is research-based. We compared ceramic reference sources, a classroom slip casting lesson, studio guides, mold and slip dealer listings and the USG data and safety sheets for its pottery plaster. We did not cast these pieces ourselves.
How slip casting works
Two materials do the work. The mold is plaster, which is absorbent. The slip is clay mixed with water and a deflocculant, a chemical such as sodium silicate or Darvan that lets the clay pour freely while holding much less water than plain clay and water would. Digitalfire defines it this way: a deflocculated, low water content slurry is poured into absorbent plaster molds, and as it sits, usually for 10 minutes or more, a layer builds against the mold walls.
Most home casting is drain casting: you fill the mold, wait, then pour the slip out to leave a hollow piece such as a mug or vase. Solid casting fills the whole cavity and is used for solid parts like handles. Wikipedia's slip casting entry notes the technique dates to China's Tang dynasty and was reinvented in Europe around 1745; factories now also use pressure casting in polymer molds, which home potters do not need.
Our clay slip guide explains how casting slip differs from joining and decorating slip, and which clays are used for it.
Slip casting supplies
The Crucible's beginner list is short: a plaster mold, thick rubber bands, slip, a pitcher, a stirrer, a bucket, dowels or a grate, a sponge and a knife. A sensible home kit looks like this:
- Slip casting molds: one-piece or multi-part plaster molds with a pour hole
- Casting slip: ready-made, matched to the cone your kiln fires to
- Mold straps or heavy rubber bands: to hold multi-part molds closed
- Bucket and pitcher: for pouring and catching slip
- Two sticks or a grate: to rest the mold upside down while it drains
- Fettling knife and sponge: to trim the pour hole and clean seams
- Scale and a 100 ml measure, or a hydrometer: to check slip density
- NIOSH-approved respirator: only needed if you mix slip or plaster from dry powder
Slip casting molds
You can buy ready-made molds from clay dealers and mold makers, buy used ones, or make your own from pottery plaster. A plain form, such as a stacking mug, is the easiest start because it has few seams and leaves a clean surface to decorate. Duncan's guidance, quoted by New Mexico Clay, says a properly cared-for mold can last 100 or more castings. Our ceramic molds guide compares slip casting molds with drape, hump and slump molds.
Casting slip (ceramic slip for sale)
Ceramic slip for sale at US clay dealers comes in gallon jugs and larger boxes, in earthenware, stoneware and porcelain. Match the firing range to your kiln. As one example, Nasco lists AMACO No. 1 Porcelain Slip as a 1 gallon, 15 lb jug fired at cone 5, white with a slightly buff tone. Ordinary throwing clay or reclaim slurry is not a casting slip; without a deflocculant it holds too much water and soaks the mold.
Sources give slightly different density targets. Digitalfire puts most casting slips at a specific gravity of about 1.75 to 1.8, while a Ceramic Arts Network guide aims for 1.80 to 1.85 for most casting. Use the figure your slip maker gives.
Slip table or slip casting table
A slip table, also called a slip casting table, is production equipment: a draining surface with rollers or a grate above a tank, often with a motor-driven stirrer and a pump that feeds slip into the molds. A potter on the Ceramic Arts Daily forum who used one found it easier to pour by hand and drain molds away from the tank, because plaster chips and clay bits kept getting into the slip. For a hobby setup, a bucket with two sticks across it does the same job. If you ever buy a powered unit, follow the maker's electrical rating and have a licensed electrician check the circuit.
Ceramic plaster for making molds
The American Ceramic Society classroom lesson makes quick practice molds from plain plaster of Paris, but for molds you will use many times, a pottery plaster made for casting is the usual choice. USG No. 1 Pottery Plaster, which USG lists for slip casting and jiggering, mixes at 70 parts water to 100 parts plaster by weight and sets in 14 to 24 minutes. See the plaster safety notes below before you open a bag.
How to slip cast, step by step
- Prepare the mold. Make sure it is clean and dry. Wipe dust out of the cavity with a damp sponge and band the parts together tightly so slip cannot leak at the seams.
- Prepare the slip. Stir it well, because solids settle. Check its specific gravity by weighing 100 ml in grams and dividing by 100, as Ceramic Arts Network suggests.
- Fill the mold. Pour in one steady stream to the top of the pour hole. The level drops as the plaster absorbs water, so top it up.
- Wait. Watch the wall build at the rim. The Crucible's guide waits 15 to 25 minutes; the American Ceramic Society lesson waits 10 to 15 minutes for a 5 to 10 mm wall. Longer gives thicker walls.
- Drain. Turn the mold over a bucket and pour out the extra slip, then rest it upside down on sticks or a grate so it drains completely.
- Let it firm. Leave the cast in the mold until it shrinks slightly away from the plaster and reaches leather hard. The Crucible gives 20 to 40 minutes.
- Open the mold. Remove the bands and lift the parts away gently. Support the piece; fresh casts dent easily.
- Trim and fettle. Cut away the spare clay at the pour hole and shave the seam lines with a fettling knife, then smooth with a damp sponge.
- Dry slowly. Dry the piece under loose plastic, then let it reach bone dry before firing.
- Fire. Bisque fire, glaze and glaze fire to the cone your slip maker states. See our bisque firing guide.
Write the pour time on a piece of tape on each mold once you find a wall thickness you like. The Crucible notes that molds get saturated after several casts, so expect to wait longer, or stop and let the mold dry, as a session goes on.
How long to leave slip in the mold
| Source | Time in mold before draining | Context |
|---|---|---|
| Digitalfire | Usually 10 minutes or more | General studio casting |
| American Ceramic Society lesson | 10 to 15 minutes | Porcelain slip, 5 to 10 mm wall |
| The Crucible | 15 to 25 minutes | Beginner studio guide |
| Wikipedia (industrial) | 40 to 60 minutes | Washbasins in factories |
The right time depends on the slip, the mold's dryness and the wall you want. Cut a test cast in half after firming to measure the wall, then adjust.
Common slip casting mistakes
- Using a saturated mold: a mold soaked from earlier casts builds walls slowly. Let molds dry fully between sessions.
- Too much deflocculant: Ceramic Arts Network warns it makes casts slow to release and leaves soft spots; Digitalfire adds that over-deflocculated slip can give weak pieces.
- Draining too early: walls too thin to hold their shape.
- Opening the mold too soon: the piece slumps or tears.
- Plaster crumbs in the slip: Digitalfire notes plaster bits in clay can absorb moisture and expand, popping out a piece of the fired clay. Screen slip that has touched chipped molds.
Safety: silica, plaster and drains
Silica: Wet slip is not a dust hazard, but dried drips and dry slip powder are. Clay contains crystalline silica. Wipe spills while wet, clean with a wet mop or HEPA vacuum, never dry sweep, and wear a NIOSH-approved respirator when you mix dry clay powder. Read the maker's SDS for any deflocculant before you handle it. Our clay dust safety guide covers studio cleaning.
Plaster: USG warns that its pottery plaster hardens and becomes very hot, sometimes quickly, once mixed with water, and that you must never make a cast enclosing any part of the body; its SDS says this can cause serious burns and even amputation. USG also says mixing dust can irritate the eyes, skin, nose, throat and upper airway, and calls for a well-ventilated area, a NIOSH-approved respirator and eye protection.
Do not pour slip or plaster down a sink. The USG SDS says to keep plaster out of drains and sewers, and slip settles in pipes just as clay does. Let plaster set in its bucket and throw it out, and catch clay water with a clay sink trap or a settling bucket.
What you need
To start slip casting at home you need one or two plaster molds, a gallon of casting slip that matches your kiln, mold bands, a bucket and a fettling knife. Our ceramic molds buying guide compares slip casting molds with drape, hump and slump molds, and lists a pottery plaster for making your own.
Sources: Digitalfire Reference Library, slip casting glossary entry and plaster material entry; Wikipedia, Slip casting; American Ceramic Society, Ceramic Processing: Slip Casting lesson (Slip-Casting-Lesson-111); The Crucible, Slip Casting in Five Steps; Ceramic Arts Network, How to Transform Your Clay Body into a Casting Slip; Ceramic Arts Daily community forum, slip casting equipment thread; Nasco listing for AMACO No. 1 Porcelain Slip; New Mexico Clay listings for Duncan DM0077C and USG No. 1 Pottery Plaster; USG No. 1 Pottery Plaster data sheet IG1366 rev. 9-17 and safety data sheet (20 March 2017). Specs checked October 2026.