What Is Clay Slip In Pottery And How To Use It?
Slip is a mixture of clay and water that forms a consistency similar to thick cream and is sometimes referred to as “liquid clay”. Slip is a little thinner than a clay slurry and contains more clay than engobe.
Clay slip might look a little yucky, the first time you work with it. But it has many uses in pottery. So it’s crucial to know how to work with it!
What is clay slip used for?
The most common uses of slip is to join two different pieces together, to decorate one of your pieces, or for pouring molds.
Let’s go over them one by one.
1. Joining pieces together
The “slip and score” technique is used in pottery to join two pieces of clay together.
The process involves scratching marks on the surface of moist clay, and then adding a liquefied clay mixture called “slip” to act as a glue. The two scored edges are then joined with light pressure, creating a bond between them.
It is important for the slip to be made from the same clay body as the pot itself, which can be achieved by making the slip from scraps of the same clay body soaked in water until they soften into a slurry, and then screened to remove lumps.
The technique is commonly used to join handles or other parts to a clay object, and is also known as slip-slurry.
2. Decorating pottery with slip
You can use slip to decorate ceramic vessels using a process called slip trailing, which involves filling a slip trailer tool with a clay slurry and applying it to the sides of the clay body.
Slip can also be brushed, sprayed, or dipped onto the object and multiple layers can be built up for intricate designs. Slip can be made of differently-colored clay or colorants can be added, and there are various commercially available dry slips.
Slip painting is beneficial as it matches the clay’s shrinkage better and is applied before the bisque firing, allowing for further underglazes and engobes to define decorations and images before the final firing.
3. Slip casting
Slip casting is a way of creating intricate pottery pieces using molds. Plaster molds are commonly used to create identical copies of a piece with complex details.
In slip casting, a thin slip is poured into a plaster mold, and the clay in the slip shrinks away from the mold’s side to form a solid shell.
The excess liquid is poured out, and the shell is left to dry overnight or until it is leather hard. The pottery piece can then be easily removed from the mold, and the mold can be washed off and reused.
Deflocculants like sodium silicate are often added to the slip to make it more solid. Slip casting is an efficient way of making multiple copies of the same item using a mold.
Types of clay slip
There are different types of clay slip depending on the ratio between the clay and the water. Each type of slip has a different purpose, composition, and consistency.
Clay slip, also known as joining slip, is primarily used for joining clay pieces together and decorating vessels. Its composition is approximately 60% clay and 40% water. The consistency of clay slip is typically a heavy cream consistency.
Casting slip is used with plaster molds to create ceramic replicas of the mold. Its composition is approximately 75% clay and 25% water. Like clay slip, casting slip also has a heavy cream consistency.
Engobe, on the other hand, is technically not a slip, although it is often categorized as a thicker, colored slip. Engobe is primarily used to add depth and color to a piece, and it is applied after bisque firing. Its ingredients include clay, water, flux, and silica. The consistency of engobe is typically thick, like that of paint.
How to make clay slip
There is no secret method to making your own slip at home. Here are 6 easy steps to making your own batch of slip.
- Collect clay scraps: Gather pieces of dry clay that can no longer be used in future projects.
- Break up the clay: Break up the clay slabs into small coin-sized pieces using your hands.
- Soak the clay: Add your clay pieces to water in a big bucket and let it soak for several hours.
- Blend the mixture: Use a kitchen blender or drill blender to mix the clay and water until it forms a smooth mixture.
- Strain the mixture: Pour the mixture through a mesh strainer to remove any lumps or impurities, making it super smooth.
- Store the slip: Keep the slip in a jar or container so that it remains smooth and ready to use for future projects.
If you want to make a different kind of slip that’s stronger and less likely to shrink, you can add a special ingredient called “soda ash”. Just add a little bit of this material to your mixture and stir it in well.
Colored slip is a type of liquid clay mixture that has been tinted with metal oxides to create vibrant colors. It can be used to add a decorative element to pottery by creating colorful designs and patterns. The colored slip can be applied to the surface of the pottery by dipping, painting or brushing it onto the surface.
To make colored slip, regular clay slip is mixed with metal oxides such as cobalt carbonate, iron oxide, or copper oxide. The amount of metal oxide added to the slip will determine the intensity of the color produced. The mixture is stirred until the desired consistency and color is achieved. Once applied to the pottery, the slip can be left as is, or a transparent glaze can be added on top of it to create a smooth and glossy finish.
Using colored slip can provide a unique and colorful addition to the surface of pottery, and can be used in combination with other techniques such as carving, stamping or sgraffito to create even more complex designs.
Storing clay slip
The best way to store clay slip is in an airtight container with a lid, such as a plastic or glass jar. This will help prevent the slip from drying out or absorbing moisture from the air, which can affect its consistency and usability. For small amounts of slip, freezer bags can work as well as long as you can seal them tightly.
It’s also important to label the container with the date and type of slip for easy identification in the future. Additionally, storing the slip in a cool, dry place away from direct sunlight can help prolong its shelf life.
Even if you properly stored your slip, you want to check on it regularly to make sure no mold is growing. Adding a small amount of vinegar or bleach may help prevent mold from growing as well.
I hope this article helped to demystify what clay slip is and how to use it.
You might want to experiment a little bit with the water to clay ratio and make your own slip clay recipe to see what works best for you.
If you are new to pottery and not sure which clay to use, you can read our full clay buyer’s guide here.
Frequently asked questions
What is slipware?
Slipware is a kind of pottery that is made by putting slip onto a clay surface that is almost dry. Slip can be applied to pottery using different methods, like dipping or painting. Slipware can be used for both glazing and decoration. Slip painting involves using slip like paint to create designs on pottery using brushes or other tools, while slip trailing involves dripping or piping thick slip onto the pottery’s surface.
What is scoring clay?
Scoring clay is a technique used in pottery to attach two pieces of clay together. It involves making shallow cuts or scratches in the surface of the clay where the two pieces will be joined, creating a rough surface that allows slip to adhere better.
By scoring the clay and applying slip, the two pieces of clay can be fused together to create a strong bond. This technique is used in a variety of pottery-making processes, such as attaching handles, spouts, or feet to a pot, or attaching parts of a sculpture. The scored and slipped area is left to dry before it is fired in a kiln, allowing the two pieces of clay to be permanently fused together.
Should you add vinegar to slip?
Vinegar is sometimes added to slip to help break down the clay particles and make the slip smoother and more workable. Vinegar is an acid, which can help to dissolve the calcium and other minerals that are often present in clay, making it easier to mix the slip to the desired consistency. Additionally, the acetic acid in the vinegar can act as a deflocculant, helping to keep the clay particles suspended in the water and reducing the need for excessive mixing or blending.