What Is Slip In Pottery?

Slip, sometimes referred to as liquid clay, is essentially a liquid mix of pieces of clay in water. It normally has a consistency like thick cream when mixed together but slip may be more liquid like dependent on what you intend to use it for.

Ceramists use slip in a variety of ways and it is a really versatile material for your ceramics project.

What is clay slip used for in pottery?

Slip can be used in three predominant ways in ceramics. It can be used for:

1. Decoration
2. Pouring molds
3. An adhesive to bond pottery pieces together

Looking at clay slip uses in more detail

Decoration

Many potters use slip as a form of decoration for their project or piece. The process of using clay slip in decoration is called slip trailing. The technique involves filling a slip trailing instrument (to be used as the applicator) with the slip, which is essentially a squeezy bottle to make it easy to apply the slip.

The clay slip is then applied to the body of the piece in a decorative fashion. Once fired, the slip creates a pattern and different texture to the surface of the clay. It’s a really simple method of adding interest and features to a piece of pottery.

Pouring Molds

Using a pouring mold is called slip casting. Slip casting is an easy method of forming intricate pieces with a mold that cannot be created by hand or on a pottery wheel. Creating a plaster mold will enable you to make identical copies, which is great if you are looking to make pottery on a commercial scale and you want to produce some uniform pieces.

Using a mold will enable you to imprint otherwise complex patterns on to your piece and also helps to create perfect shapes which may not be achievable by hand.

The basic premise of this method is to pour the slip into plaster molds, using enough to ensure that you have filled the walls of the plaster mold so that the piece comes out as you intended. The slip is then left to set and takes the shape of the mold.

An Adhesive Bond

In this instance, slip is used as a method to adhere two pieces of clay together. The best way to do this is by using a process called slip and score. The scoring element involves creating marks on the surface of the wet clay object.

The slip is then applied to the scored surface, acting as a glue between the two pieces and forming a join. The join is then solidified by applying pressure onto the piece to be attached and the scored and slip area of the ceramic piece.

What types of slip are there?

There are three main types of slip used by a potter, each with unique characteristics which suit them to the job in hand.

Clay Slip

Clay slip is the most commonly used form of slip. It is used to adhere clay pieces together and also decorating vessels. Clay slip has a fairly even concentration of clay content, with a ratio of approximately 60% clay to 40% water. When mixed in this quantity, it forms a heavy cream consistency and the mixture should run easily out of its dispenser.

Casting Slip

Casting slip is generally used to fill plaster molds. This type of slip is used in a liquid form but it has a slightly higher concentration of clay in order that it fills out the mold and sets quicker.

The ratio of clay is 75% to water which is around 25%. Again, it has a thick heavy cream consistency but is slightly thicker than clay slip.

Engobe

Engobe is not fundamentally a slip but it is often grouped in the same family. This is because Engobe acts as a colored slip and so contains more than just clay and water.

Engobe is a colored slip, generally used to add depth and color to a piece. It's also applied after bisque firing and is made up of clay, water, flux and silica.

Engobe is a thicker form of slip and has the consistency of thick paint.

How do you make slip?

Making pottery clay slips is a pretty straightforward process that can be done at home. The process is fundamentally mixing clay and water together. Here's a step by step guide for how to make your own slip:

1. Gather together any clay scraps or materials you have laying around
2. Break the clay up into coin sized particles
3. Tip the clay into the water in a bucket or similar large container and allow to soak
4. Mix the two elements together using a hand mixer or drill mixer
5. You should strain your slip to remove any lumps and to make sure that its absolutely smooth
6. Any excess slip should then be stored carefully to maintain its consistency and body and to be used in the future

Ultimately, this is a great way to reuse or recycle unused bits of dry clay. You need to ensure that you are using dry clay for this process and not wet clay.

When making pottery slip, you might want to consider what your end product is. If you are making a practical piece that requires hardwaring characteristics, then you should add soda ash. This increases the strength and workability of your pottery piece and reduces shrinkage when fired.

What is slipware? 

You will sometimes hear that a pottery piece is referred to as slipware.

Slipware is essentially pottery that has been decorated by using slip.  The term is normally for pottery items where the slip has been applied in a pattern using a brush or slip trailing.

Conclusion

So, in summary, slip is a very useful and multipurpose tool for potters. Its liquid form enables the production of perhaps much more complex textures, patterns and forms and allows you to experiment with different thicknesses and forms to see what works best for your project.

The ability to use slip to decorate your piece gives you much more scope in what you can produce.

It's also got some great practical uses, particularly when bonding two bits of clay together, which is a fairly common occurrence when making pottery.

Finally, if you want to make several pieces of the same consistency and type and you don't want them to vary, then using a plaster mold with slip is a great way to achieve consistent results.

This is particularly useful if you are producing pottery as part of a commercial venture, as your product becomes standardised and does not vary significantly from piece to piece.