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How To Recycle Clay

How To Recycle Clay

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Clay that you buy generally has the right water content.  Also, it is free from debris and air pockets.  However, potters generate waste whilst they work.  To save money, it is possible to recycle clay.  How to recycle clay is also a good question at a time when we are more conscious of the environment.

Recycling clay involves dissolving scraps of waste clay in water.  Once the clay has dissolved, the excess water is drained off.  Moisture is then allowed to evaporate from the clay body until it is workable and no longer sticky.  The clay is then wedged.  This is how to recycle clay.

What Kind of Clay Can Be Recycled?

Fired clay has been chemically and structurally changed.  When it is fired, it becomes ceramic and cannot be changed back to clay.  However, prior to a bisque fire, all clay, no matter how dry it has become can be recycled.

Some potters advocate recycling clay according to quite specific guidelines.  Other potters have a more haphazard, ‘see what happens’ approach.  To an extent, the approach you prefer will depend on what suits you personally, how you work and your circumstances.

There are many different approaches to recycling clay.  And most potters will customize their approach according to what has worked for them in the past.

Potters often recommend that when recycling clay you should separate the clay out.  The idea is that you recycle similar clays together.  They can be separated out along the following lines:

  1. How workable they are.  i.e. are they wet, leather hard or bone-dry? 
  2. Are they different colors?
  3. How has the clay been used?  Waste from building pots is likely to be in the form of scraps and offcuts.  By contrast, waste from throwing pots will likely be slop, or at least very wet.
  4. What temperature do they mature at in the kiln?

There are quite a few variables in separating clays out.  In this article, I am focusing on separating clays out according to how dry they are.  However, it is considered good practice to take the other variables into account too.

Slaking Down

It is recommended that you recycle clays with a different water content separately.  This is because clay dissolves at different speeds depending on how wet it is.  For example, bone dry clay will dissolve in water quite quickly.  The disintegrating process is called slaking down.  The reason dry clay disintegrates easily in water is that it is porous and absorbs the water easily.

By contrast, wet or leather hard clay is less porous and absorbent.  The clay particles in wet or leather hard clay are still bonded together closely.  The remaining water content in the leather hard clay holds it together so that it dissolves more slowly.

When recycling clay we are aiming to produce clay that has a homogeneous consistency.  Mixing clays that slake at different rates makes it harder to achieve an even clay body.

There are different techniques for recycling clays according to how dry they are.  I will take a look at these different techniques now:

How to Recycle If Your Clay is Almost Completely Dry

Ideally, clay has a water content of 30%.  How to recycle clay when it is completely almost dry is to put it in a plastic bag.  Then work out how much water to add.  First, weigh the bag of clay.  Then work out how much water you need to make up 30% of the total weight.

How to calculate the amount of water you need to recycle clay

Amount of Water Needed to Recycle Clay

Here is an example of how the above formula is used.  It is used to calculate the amount of water needed for a particular weight of almost dry clay.

If your almost dry clay weighs 14lb, then:

14lb/70=0.2

0.2x30-=6lb

A fluid ounce of water weighs 0.065lb.  Therefore.. 

6/0.065=92.30

To reconstitute 14lb of almost dry clay you need around 92.30 fluid ounces of water.  There are 19.21 fluid ounces in a pint.  Therefore, you will need around 4.80 pints of water for 14lb of very dry clay.

Put the correct amount of water in the bag with the clay.  Seal the bag up so it is airtight.  Leave the bag of clay and water in a bucket.  If the bag leaks and it is in a bucket you minimize mess!

Wait for around a week for the water to permeate the clay.  You need to give the water enough time to spread through the clay equally.  If you do not give it enough time, the consistency of the clay will be uneven.

How to Recycle Bone Dry Clay:

How to recycle clay

Sometimes potters will have pieces of bone-dry clay that needs to be recycled.  Other potters actually recommend that when you are recycling, you leave the clay to become bone dry. 

The reason for this is that it will all slake down quickly at a consistent rate.  Therefore, producing recycled clay with an even consistency.

It is important to remember that clay dust is not good for you. Clay contains silica, which is bad for your lungs when inhaled1

So, if you are handling large amounts of very dry clay, it is advised that you wear a mask.  If possible, it is recommended that you handle very dry clay outside rather than indoors. 

That being said, here are some techniques for recycling bone dry clay…

The Bucket Method

There are a few different variations on the bucket method of how to recycle clay.  Potters will often tweak their recycling techniques over the years.   I have included a few variations of approach in the following description of the bucket method.

Break up the pieces of clay so that they are no more than 1 inch big.  Transfer these pieces into a strong bucket.

It is sometimes suggested that you use a heavy-duty refuse sack to line the bucket.  This makes it easier to get the clay out one it is wet and heavy again.

Add enough water to amply cover the clay.  Some potters prefer to tip the clay into the water rather than pouring the water over the clay. 

Once there is sufficient water covering the clay leave it for a few days.  Gradually the clay will break down.  Bone-dry clay can slake down in a matter of hours.  However, it is often recommended that you leave the clay for 3-6 days2, to ensure that it has dissolved completely.

To Mix or Not To Mix, That is the Question

Some potters prefer to leave the bucket to its own devices as the clay dissolves.  They suggest that there is no need to mix the slurry.  Others claim that it is necessary to mix it to give the clay an even consistency. 

If you choose to mix the clay you can use a number of implements.  You can keep it simple and use a stick to mix it.  Or you can go high tech and use a drill with a mixing bit on the end as an attachment.

Sieving The Slurry

If you feel confident that the clay does not contain debris and bits you can now let it settle.  However, if you are concerned that the consistency is not very even.  Or if you think that there may be unwanted items in the bucket, then you can sieve the mix. 

To do this, simply transfer the mixture from one bucket to another through a piece of mesh.  You may need to push the slurry through the mesh with a spatula to speed the process up.  

After sieving, let the mix settle.  You need to wait until the excess water is sitting on top of the clay sediment.  Then the water needs to be removed.  There are multiple ways of doing this.

Getting Rid of the Excess Water

If the bucket is not too heavy you can carefully pour the water off.  However, it is best not to disturb the clay sediment.  Another way of removing the water without tipping the bucket is to absorb the water into a sponge.  You can also use a ladle, or a pipe to siphon it off.  If you have the patience you can use a turkey baster or a bulb syringe for smaller quantities.

Once the water has been removed, it is a good idea to let it more water evaporate.  There are a few ways to do this.  One way is to transfer the slurry into a wider container.  This gives it a bigger surface area for the water to evaporate from. 

Another way is to poke holes into the clay sludge in the bucket.  Over the course of a few days poke additional holes in the clay.  This enables the water at the bottom of the bucket to evaporate and escape too.  

Allow the slurry to sit for a few days, stirring occasionally.  Once it has thickened up a bit and it is no longer sticky it will be ready to dry out. 

If the clay is in a thick bag in the bucket, you can slide the bag out of the bucket.  If it is not in a bag you will likely have to scoop the clay out for drying.

Drying The Recycled Clay

To dry the clay out enough to make it useable, it needs to be spread out onto an absorbent surface.

A variety of absorbent surfaces are suitable.  A common method is to spread the clay out onto plaster bats.  However, if you do not have plaster bats, you can spread the clay onto an old towel, or some canvas.  If the towel or canvas becomes very wet before enough water is absorbed, you may need to change it. 

You can also wood, drywall or Hardie board.  Basically, an absorbent surface, that will not disintegrate in the water or add contaminants to the clay should be ok.

Here is a great video on how to make your own simple plaster bat:

Potters vary in how thick they recommend the clay to be spread out.  But generally, it is recommended that the layer is somewhere between 2 to 4 inches thick.           

You can dry your clay out inside or outdoors.

Ways to Speed Up the Drying Process:

  • Leaving outside (especially if it’s a warm day)
  • Using a fan indoors
  • Putting the absorbent surface onto a rack so that air circulates underneath it.

It is recommended that if you are drying your clay outside, that you cover it with a breathable cover.  This will prevent bits like leaves and dirt from falling into the clay.

It is important to check that the clay is not drying out too quickly.  Clay on a plaster bat will dry out fast.  It is recommended that you check the clay every 15 minutes or so.  You will need to turn the clay so that the reverse side also dries out.  The clay is ready to turn when it peels off the absorbent surface, without leaving a sticky mess.

The clay at the edge is in danger of drying out quicker than the clay in the center.  You can help avoid this by pressing the edges in a bit.  This will make the edges a little thicker than the center and will ensure that it dries slower. 

Once turned and dried on the reverse side, the clay is ready to be balled up and wedged.  The clay is ready if you can make it into a moldable ball that doesn’t stick to your fingers. 

To remove the clay from a hard surface like a plaster bat you may need to scrape it off.  If you are scraping, make sure to do this carefully.  You don’t want to scrape any plaster or debris into the clay as it is being lifted off.  The clay will peel of a towel or canvas easily.

Once the clay has been removed from the absorbent surface it is ready to be wedged and put into storage.

The Bag Method of How to Recycle Clay

One variation on the bucket method of how to recycle clay is as follows3.  Collect your scraps in a bucket.  When the bucket is full and the scraps are dry, break the pieces into even-sized chunks. 

Then take handfuls of dried clay and whilst holding onto the clay dunk it in water.  Keep the clay submerged for a few seconds until it has had a chance to absorb some water.  Then transfer the wet clay into a strong plastic bag.  Complete this process until all the clay has been submerged and bagged up.

Seal up the bag and leave it overnight.  After 24 hours the clay should have become a sticky mixture.  This can then be dried out on plaster bats, or on whichever drying method outlined above you prefer.

Reasons Not to Let Clay Get Bone Dry Before Recycling

Not all potters let their clay dry out completely before recycling.  Clay slakes down more quickly when it is bone dry.  However, when clay dries out, it loses a lot of the water between the clay particles.  The water sits between the particles and bonds them together.  It also contributes to the clay’s plasticity.

Clay is wet once it has been through the recycling process.  However, it takes a lot longer for the water to migrate back properly between the clay particles.  Until the water has been thoroughly absorbed in this way, the clay will be less plastic.  This can take a couple of months, and in the meantime the clay is not as workable as non-recycled clay. 

Recycling Wet or Damp Clay

If you decide to recycle wet or damp clay, you can use a bucket method similar to that outlined above.  Simply, put the wet and sloppy clay in a bucket with some water in it. 

The scraps sit in the water mix and break down into an even consistency over time.  Wet but solid pieces can be put directly into the bucket.  A mesh can be placed on the top of the bucket.  Very wet clay and slop can be put onto the mesh and sieved on their way into the bucket. 

As outlined above, once your bucket starts to get full leave the clay to break down as much as possible.  Once the clay has dissolved, the process is the same as the one described earlier.

Recycling Slop and Very Wet Clay

Very wet clay is referred to as slop.  This is extremely liquid and is close to having the consistency of slip.  One method of how to recycle clay slop is to put it into a pillowcase.  The pillowcase is then suspended above a bucket. 

The water in the clay then drains out of the fabric into the bucket below.  Once the clay has reached a sludgy consistency, it can also be dried out further on an absorbent surface.

Some potters leave the pillowcase hanging until they feel that the clay is dry enough to be wedged.  By doing this they manage to skip the stage of spreading the clay on plaster bats.  You can test if the clay is ready to wedge by poking the side of the pillowcase.  If your finger leaves an indentation in the clay, you know that it is beginning to become workable.

Another tip if you are using this method to recycle clay, is to turn the pillowcase inside out.  This removes the chance that thread and lint from the pillowcase seams will get into the clay. 

Recycling Mixed Clays

how to recycle clay

Some potters do not have the time or resources to separate clay out before recycling.  An example of this would be a school environment.  As such they may choose to recycle dry and wet clay together.  And this is one technique that can be used if time and resources are short:

How to Recycle Mixed Clay

Place all your waste clay into a large robust bucket.  If you are working in a busy environment like a school, a large bucket or container on wheels is useful.  Wet clay is heavy, and if you are moving large quantities around, a container on wheels will save your back.

Simply put your waste clay into the container.  If you are picking waste off the floor be selective.  Don’t put clay into the container that is contaminated with dirt or bits of fired clay.  A mesh frame across the top of the container is very useful in this context. 

Big pieces of clay can be put straight into the bucket and wet clay can be placed on the mesh to filter through.

Add sufficient water to the bucket to keep the clay in the bucket submerged at all times. 

As stated above, there is debate amongst potters about whether mixing is necessary.  However, when recycling mixed clay, stirring the slurry before drying it out is a very good idea.  You are more likely to get a homogeneous clay body if the clay has been mixed well before drying.      

Wedging and Storing Your Recycled Clay

how to recycle clay

Once the clay has dried enough to be removed from the absorbent surface, it will need to be wedged.  Some potters argue that if you use clay to build you do not need to wedge it.  Only clay that is going to be thrown on the wheel requires wedging. 

However, others argue that it is a good idea to wedge all recycled clay.  Wedging gets rid of air pockets.  But also, it improves plasticity, which can be lost in the recycling process.   There are a number of different wedging techniques, outlined here

One suggested method3, is as follows:  First, flatten your clay with your fists until it is about two inches thick.  Then use a rolling pin to even out the clay and make it even thinner.  When the clay is quite thin you will be able to see the air bubbles under the clay surface.  They look a bit like blisters in skin.  You can prick these with a pin or a sharp modeling tool to get rid of them. 

If you are not going to use the recycled clay immediately, you need to store it.  The best way to store clay is to put it into a thick plastic bag and seal it.  Then put the plastic bag into an airtight container.  Air can still pass through a plastic bag, so over time clay will dry out a little.  By putting the bag in an airtight container, you are minimizing how much it dries out in storage. 

Final Thoughts

Recycling clay is not the most glamorous aspect of pottery.  However, it can feel very rewarding and it is better for the environment.  Many potters approach how to recycle clay in their own individual way.  I would recommend giving it a try and seeing what works for you.  After all, if it doesn’t go to plan, you can always recycle it!

References:

1. https://ehs.princeton.edu/health-safety-the-campus-community/art-theater-safety/art-safety/ceramics
2.https://www.wikihow.com/Recycle-Ceramic-Clay-Using-the-Bucket-Method
3.http://lizcrainceramics.com/2017/08/reclaiming-clay-a-rationale-and-pictorial-how-to/