What Is Slip in Pottery and What Is It Used For?

What slip is

Slip is made by mixing clay with water until it has the consistency of cream, sometimes thinner or thicker depending on use. It is typically made from the same clay as the pot, or from a compatible clay body, so that it shrinks at a similar rate as it dries.

Because it is wet clay, slip bonds well to damp clay surfaces. It dries and fires with the pot, becoming part of the finished piece.

Slip for joining

The classic use is to attach parts. Scoring means scratching both surfaces with a tool, then applying slip to act as glue before pressing the pieces together. This is how handles, lugs, spouts and coil joins are made. The roughened surfaces and the slip create a strong bond.

Some potters prefer a thicker slip called a slurry, or a mix made with a bit of vinegar. Whatever method you use, join parts that are at the same stage of dryness.

See slip and magic water →

Decorative slip

Colored slips are made by adding oxides or stains to a white or light clay slip. Applied to leather hard pots by dipping, brushing or trailing, they create bright or subtle surfaces. Slip trailing, where slip is squeezed from a bottle to draw raised lines, is a popular technique.

Slip can also be carved through in sgraffito, revealing the clay below. The contrast between the layers makes simple designs look striking.

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Casting slip

Slip casting is a separate process that uses a special liquid clay called casting slip, which contains deflocculants that allow it to flow with less water. It is poured into plaster molds, which absorb water from the slip and leave a clay layer on the mold walls. After a while, excess slip is poured out and the piece is removed.

Casting slip is not the same as slip made by mixing water and regular clay, so do not substitute one for the other when casting. Always follow the supplier's instructions for mixing and use.

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Making and storing slip

To make a basic slip, take dry or scrap clay, soak it in water and mix until smooth, then pass it through a sieve to remove lumps. Adjust the water until you reach the desired consistency. Store the slip in a lidded container and stir before use.

Label containers with the clay type so you do not mix them. Slip made from one clay body should only be used on compatible clays. Wear a dust mask when handling dry clay powder.

Tips for clean application

Apply slip to leather hard clay for the best adhesion and the least cracking. Use a soft brush and thin, even coats. If the slip is too thick, it may crack as it dries, and if it is too thin, it may be patchy.

Test your slip and glaze combination on a tile before using it on a finished piece. Some colored slips affect glaze color and fit.

See brushes for slip and glaze →

Slip versus engobe and underglaze

You may see the terms engobe and underglaze alongside slip. An engobe is a type of slip that has been formulated, often with additional materials, to fire at a certain temperature and sit under a glaze. Underglaze is a commercial colored decoration product designed to be applied under clear glaze and usually has a different feel from slip.

All three can add color to the surface, but they behave differently. Slip is the simplest, an actual clay mixture, while underglaze is more convenient and consistent for detailed painting.

If you want predictable color, underglaze is often the easier route. If you like the traditional clay-based look, slip is worth learning.

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Common problems with slip

Peeling or flaking usually means the slip was applied to clay that was too dry or the slip was too thick. Cracking can happen if the slip shrinks more than the body. Pinholes can appear when slip dries too fast or when trapped air escapes.

Match the slip to the clay, apply it at the right dryness and dry slowly under loose plastic. If you are unsure, test a few combinations before decorating important pieces.

Slip in a home studio

A simple slip station needs a bucket with a lid, a sieve, a few brushes and a stirring stick. Keep it away from your throwing area so dry residue does not float as dust. Clean up with damp cloths, and avoid pouring slip down household drains, because clay can clog pipes. Let sediment settle in a bucket and dispose of the solids with the trash or reclaim them.

Wash your hands after working, and keep slip containers closed to prevent evaporation and spills, and label each one with the clay it contains so nothing gets mixed up by accident.

Frequently asked questions

Is slip the same as glaze? No. Slip is liquid clay that stays clay after firing, while glaze melts into a layer of glass that seals and colors the surface.

Can I use slip on dry clay? It is harder, because dry clay absorbs water quickly and may crack. Leather hard works better.

Can slip be food safe? Slip itself is clay, but pieces for food need a food safe glaze over the top, fired to the right temperature.