The 7 Stages of Clay

From its origins through to a finished piece, there are 7 stages of clay which your clay goes through before it becomes a finished ceramic.

Here, we guide you through the different stages of clay to help you understand the entire stage process.

The Dry Clay Stage

Dry clay usually comes in powder form and is processed through fine particles that have been formed over millions of years from volcanic ash. In pottery, the most common dry clay used is called ball clay. Ball clays generally contain quartz, titanium, mica, kaolinite, iron, and some other minerals.

The removal of moisture means that it's a dry clay and therefore will never go off. You can store dry clay forever. You can also modify dry clay easily as many different elements can be added to it including grog, fine sand, and colorants before you mix it with water.

It's light and easy to ship, so it isn't as expensive as wet clays and you can make it to your own desired texture.

The Slip Clay Stage

Slip clay is essentially watered down clay that is more liquid in its form. It is generally like heavy cream or paint. It has a number of key uses in pottery and is a real multipurpose form of clay.

Slip clay can be used in a number of ways, including:

• An adhesive to stick clay together or to use as a repair tool
• For decoration purposes, usually applied by hand to give texture
• For casting using a plaster mold

The beauty of slip clay is that it can be made from old bits or off-cuts of clay, simply mixed together with water to create the desired consistency.

The Plastic Clay Stage (Also Known As Wet Clay)

Plastic clay is used by many potters as it is drier than slip but still wet enough to easily mold and shape into different forms. Once molded, it will keep its shape and so is perfect for ceramics of all purposes. It's a highly workable form of clay.

Plastic clay (wet clay) is the type of clay generally used for pottery and for throwing or molding. Plastic clay can be made from dry clay, using the dry clay mix and water to create the plastic stage consistency.

Slip can also be turned into the plastic stage by removing some of the moisture in the slip. It is essentially a very thick form of clay and is the type that you would expect to see in a pottery workshop.

The Leather Hard Clay Stage

The leather hard clay stage is what occurs when the clay dries out. At this stage, the clay will be much drier and will not be marked when touched.

The leather hard clay will feel dry and cool to the touch, much like leather, where it gets its name. The clay can be carved or turned at this stage, so care should be taken.

At this stage you can trim your piece, add embellishments or handles before the clay becomes too hard and unworkable.

You need to carefully judge the texture at this stage to ensure that it is not too wet, which will make adding things to it difficult, or too dry where it is difficult to attach things or trim without breaking it.

Letting it get too dry is the worst of the two possibilities as once it has dried too much it will have gone past the stage of being workable and will no longer be soft enough to be pliable.

If you want to slow down the drying process, you can do so by wrapping the clay in plastic.

Further Reading: How To Dry Pottery Clay

The Bone Dry Clay Stage

The clay at this stage is absolutely bone dry and is suitable for firing.

The clay at this stage is sometimes referred to as greenware. It is hard but can still be brittle before firing. 

At this stage, you can still recycle your clay but once it is fired, the clay cannot revert to a previous stage.

Underglaze can be applied at this stage before firing but it needs to dry thoroughly before firing.

To reach this stage, the clay needs to dry out naturally. This can take a week or longer, dependent on the climate, for clay to move from the leather stage to the bone dry stage.

You need to ensure that the clay is completely bone dry. Fired clay that is not completely bone dry can explode in the kiln through expansion, so take care to leave this stage as long as possible.

The Bisqueware Stage

The bisqueware stage of clay is reached once it has been fired in a kiln.

The bisque stage permanently changes the form of the clay and so you can not go back after this stage. The process involves firing the clay to remove any chemically bonded water in the clay.

The bisqueware stage is the ideal stage for glazing. The clay has hardened to a point where it can accept the application of glazes but is still porous enough to absorb the glaze.

To prepare your bisque pieces for glazing you will need to clean them down first to make sure any dust is removed which could affect the glazing process. You need to throughly dry your piece before glazing.

This is the perfect stage to apply underglaze. Before adding a clear glaze over the top, make sure that the underglaze is completely dry. If you have already underglazed at the leather hard clay stage, this is the perfect opportunity to reapply to ensure a good covering.

Final glazing can be applied through dipping, brushing or spraying. There are a number of different color and application techniques that you can use at this point.

Take care to apply enough glaze to create the effect that you want at this stage.

The Glazeware Stage

The glazeware stage of clay is the stage where clay has undertaken a final firing called the glaze firing.

Glazing firings are done at different temperatures, dependent on what finish you wish and what type of clay you are using.

The three different temperatures are:

Low fire 

• The low firing stage is usually at cone 04 with a temperature of around 1800 degrees. If you fire your clay too hot, it will melt in the kiln and ruin your piece.

Mid-fire

• A mid fire firing stage is around 2200 degrees, cone 5 or 6. A clay at this temperature needs to be able to resist medium to high temperatures.

High Fire

• High fire stage of firing is around 2380 degrees or cone 10. The clay needs to be able to withstand cone 10 heat otherwise it will melt.
• You do not want to clean up melted glaze all over your kiln!

Summary

If you are a potter or you use clay on a wheel to make pots, then it's important to understand how your clay changes through the different processes. Different types of clay can reach these stages at different points, so it's best to experiment with your clay to ensure that your end product is as you had intended.

At various stages of clay, you are likely to require a kiln. Soul Ceramics has an extensive range of electric fired kilns, perfectly suited for drying out clay or glazing. Please do not hesitate to get in contact with us if you are looking for a kiln for your next project.