How to wedge clay

How to Prepare Clay for Pottery

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So, you are getting ready to throw your first pot on the potters wheel.  You have heard that it can be difficult to center clay on the wheel.  And you have heard about pottery exploding in the kiln because the clay ‘wasn’t quite right’.  You are probably asking yourself how to prepare clay for pottery and avoid things going wrong.

Clay needs to be pliable and clean, with an even consistency.  It needs to have the right water content, and not contain air bubbles.  Wedging is an essential step in how to prepare you clay for pottery.  It can help adjust the water content, consistency and air pockets in clay.  

In this article, I will look at exactly what steps you need to take in order to get ready to do some pottery!  This involves getting your clay, your space and yourself prepared in a few simple ways.  So, read on…

Clay needs to have a few qualities to be coopeartive on the potter’s wheel and in the kiln.  These qualities are as follows:  

Making Your Clay Pliable

Clay should be soft and pliable but not too wet and sticky.  A new bag of clay, in theory, contains the right amount of water for that clay body.  This is normally around 30% of its body weight. 

What if Your Clay is Too Wet?

How to prepare clay for potteryIf your clay is very sticky and soft, it will need to be dried out a little.  The clay should be firm but pliable and malleable.  You can dry clay out in a few ways.  If you don’t have much equipment, then the simplest way to dry clay out is as follows.

Roll or spread the clay out and allow it to air dry for a while.  Continue to check it so that it doesn’t get too dry.  Remember that it only takes a week for clay exposed to the air to become bone dry.  So, drying it sufficiently to throw it, won’t take that long. 

You can speed the drying process up by spreading it on an absorbent surface.  You can get wedging tables which have a specially designed plaster surface for this purpose.  If you have a wedging table roll the clay onto the plaster surface. 

If the clay is very wet, you will need to leave it until it can be lifted off in a pliable slab.  It is advised that you do not scrape clay of the plaster surface.  If you scrape the clay up, little bits of plaster from the table can get stuck in the clay. 

Clay dries quickly on plaster.  Therefore, you need to check the clay frequently.  By checking every 15 minutes or so you ensure that it is not drying out too much to be workable. 

A wedging table is useful kit and part of how to prepare your clay for pottery.  However, if you don’t have a wedging table, you can use another absorbent surface, like a concrete floor.  Just make sure that the surface is clean of dirt and debris.  

What if Your Clay is Too Dry?

Clay that is sitting around dries out.  Clay dries out, even if it is in a plastic bag.  Once the bag has been opened and sealed again, the clay will dry slowly.  As clay dries, it hardens and becomes less workable. 

I had a bag of clay sitting in my cupboard for a few years.  It was sealed, so it was still wet, but it had become more solid than I needed it to be. 

How to prepare dry clay for potteryIf clay is in the open air, it will dry out completely.  This is referred to as being ‘bone dry‘.  How long this takes, depends on how big the piece of clay is.  But eventually, even a large slab will become solid. 

If you are new to pottery, chances are the clay you will be using is new too.  Potters who have been working for some time will have bits of leftover scrap clay and slop.  Making pottery is a messy business, and clay gets discarded along the way.  Provided waste clay is not too contaminated with debris it can be recycled. 

Old bits of waste clay can dry and become very hard.  Reclaiming bone dry clay involves a particular method called slaking.  However, if your clay is only a little dry then either of the following methods can help:

How to Moisten Clay

  • To moisten it up, you can wrap it in a wet towel.  Then put the clay and towel it in a sealed plastic bag.  Let this sit for a week or so.  The clay will gradually absorb the water and soften. 
  • You can sprinkle water on the clay and then knead it until it feels more malleable.

The correct term for kneading clay is called wedging.  The term kneading is often used to describe how to prepare clay for pottery.  However, some potters do not like the use of the term kneading.  This is because when we knead bread we are trying to get air into the bread. 

By contrast, we wedge clay to try to get the air bubbles out.  Kneading and wedging are designed to do different things.  They do however look similar, so it is understandable why the parallel is drawn.      

Getting Rid of Air Bubbles to Prepare your Clay

In theory, a new bag of clay does not contain air bubbles.  When clay is bagged up in a factory, it is packed with a vacuum extruder which takes out any air bubbles. 

Here is a video of clay being produced by an industrial vacuum extruder.  Is it me, or is it weirdly satisfying to watch? 

By contrast, clay that has been collected up as waste from projects in a potters studio probably does have some air pockets.  Never the less, even if your clay is brand new, it is still a good idea to wedge it.  There may be some air pockets present. 

It is important to remove air bubbles is that they cause your piece to explode in the kiln.  It is part of received wisdom and often said that air bubbles in clay cause clay to explode. 

In fact, lots of potters disagree with this.  They point out that actually what causes explosions is moisture in the clay.  Water in clay turns to steam at boiling point.  Residual moisture in the clay expands quickly at 212F and can cause pottery to shatter. 

Air bubbles themselves do not cause the clay to explode.  However, moisture in the clay can migrate into the air bubbles when the clay reaches boiling point in the kiln.   At this temperature, the water expands sharply in the pockets.  Explosions happen if the firing schedule is too quick, and the clay doesn’t dry out in the preheat.  So, it is important to be sure that air bubbles are removed. 

Below is a video of clay being produced by an industrial vacuum extruder.  Is it me, or is it weirdly satisfying to watch? 

How to Wedge Clay

There are numerous ways of wedging clay.  Finding a method that you are confident with is an important part of how to prepare clay for pottery.  Two common ways of wedging to prepare your clay for pottery are as follows:

Forward Wedging or Ram's Head Wedging:

Cut off a manageable sized chunk of clay from your block using a wire cutter.  Unless your hands are very strong, I would suggest a piece about 8 by 4 inches, in the shape of a brick.  However, you can use any sized piece of clay that you feel you can handle. 

Pat and drag the clay along a clean dry work surface until it is brick-shaped.  Then hold the clay so that it is resting on one of its edges.  Put the palms of your hands so that they are gently cupping each end of the brick.

The balls of your hands should be resting against the side of the brick.  Then push the clay away from you and down.  It is important not to push the clay straight down towards the table.  Rather push it away from yourself towards the opposite wall.  This will roll and squash the clay against the surface you are using.

Then use your fingers to lift the clay up and roll it back towards you.  Repeat the process, pressing the lump of clay down with the palms of your hands.  Apply enough pressure to knead air bubbles out.

Kneading or Wedging - A rose by any other name?

It is important not to fold the clay over on itself as this will fold more air into the clay.    When we knead bread, we fold it over on itself to put air into the bread.  When we wedge, we are careful to push the clay away and down without folding it over. 

A new piece of clay should be kneaded like this until it feels more malleable.  The air bubble should have been pushed out after around 20 rolls.  However, the longer you can keep the wedging going before you get too tired, the better.

How to prepare clay for pottery by wedging

Image by Glen Bledsoe.   “Wedging Clay‘.  Some rights reserves.  See license here:  (CC BY 2.0)

Spiral Wedging or Shell Wedging:

With shell wedging, you end up with a piece of clay that looks like a shell.  Start with a brick-shaped piece of clay.  Stand the brick upon its narrow end. 

Put your hands in a butterfly shape over the top of the clay. Then press the clay away from you at an angle.  As you lift the clay up from the surface, rotate the clay.  After you have lifted and rotated the clay, push away and down again. 

Here is a clear video demonstrating how to wedge clay in these two different ways:

Your Wedging Surface:

Wedging table – Wedging involves a lot of arm and shoulder action.  For this reason, it is important to use a table that is at the right height for you.  Ideally, the table should come up to between the very top of your legs and your hip bones. 

If your table is too high, you will not be able to apply pressure to the clay easily.  And if your table is too low, you will end up hunching forward, which will feel awkward and uncomfortable.

It is possible to buy tables specially designed for wedging.  If you have the space and budget to buy one of these, then that is great.  But if you do not, then a piece of concrete board placed on a regular table will do well.  Concrete board is very absorbent, so it is a good idea to mist it with water before you begin.  If the board is a little wet, it will not suck too much moisture from the clay. 

Alternatively, you can simply use a regular laminate kitchen surface, provided it is clean and free from breakfast crumbs!

Clay Needs to be Homogeneous

Another quality that wedging facilitates is homogeneity in the clay.  If clay has a mixture of consistencies, it can be hard to throw on the potters wheel. 

This is because when you are throwing a pot, you are applying pressure to the clay.  If some clay is very soft and other areas are hard, it will be hard to apply even pressure.  And it will be hard to get an even result in a thrown pot.

Working the clay through wedging distributes water and spreads the clay particles evenly. 

Another related function of wedging is that it helps align the clay particles.  Clay is moldable because clay particles are flat.  When flat surfaces are wet, they stick together.  Imagine two glass slides in a biology lab.  If the slides are wet, they stick together with a strong bond.  The same is true for flat clay particles.  Water between the particles holds them together. 

Also, because clay particles are flat, they hold a small electrical charge.  This charge means that clay particles are attracted to one another and stick together.        

When a clay is wedged, the particles become more uniformly aligned.  When the clay platelets are going in the same direction, it is easier to throw.  Clay with aligned particles has more plasticity and will mold more easily.  This is another reason why wedging is an essential part of how to prepare clay for pottery. 

Final Thoughts about Preparing your Clay for Pottery

Clay that is from a new bag will need less attention than clay that has been used before.  If your clay has been in storage for a while, even if it is in plastic it will need preparing.  Exactly how to prepare clay for pottery depends on its condition. 

However, regardless of what your clay looks like to start with, workable clay has a few key qualities.  Ideally, the clay needs to be malleable, free from air bubbles, and have a consistent quality. 

Thankfully, clay is forgiving.  Provided the clay does not contain debris and old bits of fired clay, it can be made workable again.  

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Pottery Tips from the Pottery Wheel

Lesley

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Pottery Tips from the Pottery Wheel

I’m Lesley Milne, the creator of The Pottery Wheel.  Like many people, I used the potter’s wheel at school.  But then I began to focus on clay sculpture and I left the wheel behind.  However, more recently, I found myself being drawn back to pottery and the potters wheel.  And so, I have tried to pick up where I left off all those years ago at school. This blog is a chronicle of what I have learned as I got back into the potters saddle!

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