A Low Tech System for Recycling Clay Scraps

As clay artists, we’re so lucky that we can reduce the amount of waste we produce by reclaiming or recycling our unfired clay.

(I use the words “reclaim” and “recycle” interchangeably.)

When we make something that cracks, warps or doesn’t look how we wanted it to, we can reclaim our clay, bringing it back to its original state so we can start over. As long as the clay hasn’t been fired yet, it can be recycled.

In this article, I’m going to describe the low tech system I use for reclaiming my clay scraps in my home studio.

My home system is different than the system we use at the public studio where I work. The public studio has many different users, different clay bodies and a big expensive machine called a pug mill that mixes our clay for us. I’ll describe that system and how it’s different in a separate article.

At home, I use a system that requires no fancy equipment, just a bit of time and effort.

Plasticity vs “Short”

For a number of years, I was diligently going through the motions of reclaiming large buckets of clay scraps a couple times/year. But I kept making one major mistake that resulted in really crappy (for lack of a better word) recycled clay.

A better term for this crappy clay is “short”. Short is the word that’s used to describe clay that has low plasticity, where clay is prone to cracking when bending, stretching and shaping.

If you roll a coil of clay and then bend it, it should bend nicely and not crack. If it does, it’s considered short.

Same goes for cutting a thick slab from a block of clay. If you bend it and stretch it, it shouldn’t crack like this clay did. This clay is short.

Plasticity refers to a clay body’s ability to be formed into a shape, and to retain that shape. Clay is what’s called a “plastic” material.

I know, it can be confusing to refer to clay as “plastic” when your brain has an idea of what plastic means. We might hear the word “plastic” and immediately think bad thoughts of killing the environment. But in ceramics, plastic = good!

Plasticity is not to be confused with “elasticity.” Elasticity refers to a material’s ability to be stretched or deformed and then return to its original shape. Plasticity means it retains the new shape.

A clay body that has sufficient plasticity will not crack when it is bent or stretched. 

Here’s a general description of how the plasticity of a clay body works:

Wet clay particles attract each other like magnets. Water allows the particles to move and slide and stay stuck together as we shape the clay.

The other thing that’s required for plasticity is what’s called “clay particle size distribution”.

The better the distribution is of small, medium and large clay particles, the more points of contact we have between all the particles, and the better our clay will stay stuck together.

Here are some graphics to help explain what I mean. Note that clay particles are flat and not round, but you get the idea.

          

When we only have one size of clay particle, there are a lot of gaps in between them and less overall points of contact bonding the clay body together.

If we bend or stretch a clay body containing only one particle size, because there are fewer bonds, a lot of them will break, causing cracking. This is what happens when clay is short.

When we have a mixture of particle sizes, the small and medium particles fill in all the gaps between the large particles and now we have more points of contact holding the clay body together.

Remember, wet clay particles attract each other like magnets so the more points of contact, the stronger the overall bond throughout that clay body will be.

When clay is short, it means there aren’t enough points of contact, holding the clay together. There are gaps that show up as cracks in the clay.

“What the heck does this have to do with clay recycling,” you ask? Well, understanding how plasticity and clay particle size distribution work will help you to make sure you’re not producing “short” reclaimed clay like I was.

My Big Reclaiming Mistake

I mentioned earlier that I kept making a major reclaiming mistake that resulted in short and unworkable clay. The mistake I kept making was discarding my throwing water.

DO NOT THROW AWAY THE CONTENTS OF YOUR THROWING BUCKET

Let me explain the reason I was throwing this away and then why you should keep it.

One time in my early days, before I understood how clay bodies and plasticity worked, I tried reclaiming just my throwing bucket. I poured the water off the top, spread the sludge onto a plaster slab, let it dry out a bit and then tried working with it.

The resulting clay was a cracking, crumbling mess for reasons that are now obvious to me. But because this process resulted in disaster, I decided that the clay in my throwing bucket was useless and problematic.

I stopped adding my throwing bucket to my reclaim bucket and just threw it into my discard bucket where I dumped old glaze tests and clay that fell onto the dirty floor, etc.

The issue (and the benefit) of the throwing sludge is that it contains the smallest clay particles. A lot of the tiniest particles are removed during the throwing process and end up in the throwing water.

Without saving the throwing water, my reclaim bucket was lacking those smallest clay particles that contribute to the overall plasticity of the clay. I was throwing all those small particles away and then complaining that my clay was crappy.

Now that I know better, I keep absolutely everything. My throwing bucket, the contents of my splash pans, any clay that comes off my thrown pots with a rib, they all go into my reclaim bucket.

I don’t worry about how much water ends up in there. When I need more space in the bucket and there’s a lot of clear water on the top of the clay, I’ll siphon it off.

Water is very good for clay recycling and I’ll explain why down below when I describe my whole reclaim process.

If your throwing bucket has settled so there’s a layer of clear water on top, you can pour that off. Just don’t remove any clay particles. If the water is cloudy, it’s because of light, floating clay particles. You want to keep the cloudy water but if it’s clear, it can be poured or siphoned off the top.

I hope you can learn from my mistakes and have the best recycled clay possible. To do so, just keep adding everything to your reclaim bucket and then follow my instructions below.

What to do with short clay?

If you have clay that you think is short and you’re having trouble working with it, I would try mixing the short clay with some fresh clay out of the bag. I’d start with half and half and if it’s still not better, mix some more fresh clay in.

Hopefully that will work well enough that you can use up that short clay and your recycled clay will be better going forward.

My Clay Recycling System

I throw a very persnickety translucent porcelain off-the-hump (which means I can’t compress the bottoms while throwing) so if my clay’s short or not well mixed or off in any way, it will definitely let me know.

It’s important to me that my recycled clay isn’t more persnickety than what I’m starting with.

The system I use is thorough and may take more time than other ways of doing it. To me, it’s worth the extra time and effort. Short clay is frustrating and consumes more of my energy.

My system is also portable which is great if you work in a small space.

There are many ways to reclaim your clay scraps and you can adapt and create a system that works best for you. 

Tools and supplies:

Here are the tools and supplies that I use:

  • A bucket for your reclaim
  • A drill with a paint mixing attachment
  • A glaze sieve and long-handled scrub brush
  • A plaster slab
  • A 38L blue Rubbermaid plastic tote
  • Wooden blocks
  • Plastic squeeze clamps
  • An old bed sheet

 

1. Make a plaster slab

If you don’t already have one, make a plaster slab that you can use to dry out your clay recycling. I made this one out of pottery plaster that I bought from my ceramic supplier. 

I mixed up the plaster with water and poured a 2” layer straight into the bottom of a big blue Rubbermaid tote. The plaster then hardens and because the tote is flexible and tapered, the slab pops right out.

You can use other containers or cottle boards and clamps to make a plaster slab. Whatever works for you. I use the same tote for pouring my plaster slab and my recycling process so they fit together perfectly.

I made a few of these plaster slabs that I use both in my damp boxes and for recycling clay.

If you’ve never made plaster before, search Google or YouTube and there are plenty of articles and videos that can show you how. It’s really easy, just add water, mix, pour and set.

 

2. What to put in your reclaim bucket

I use a large bucket for my reclaim, one that’s big enough to dump my splash pans into after throwing. A 10-gallon bucket works well for this.

If you use different clay bodies, be sure to have a labeled bucket for each one.

In the bucket, I dump my throwing water, handle pulling water, the contents of my splash pans, any clay that comes off my thrown pots with a rib, my trimmings, slab cutting scraps, etc. All clay scraps.

With the throwing and handle pulling water, I usually allow the clay to settle overnight and pour the clear water off the top before dumping in the reclaim bucket.

Any clay that has dried past the point of wedging, I let dry out completely and then I throw the bone dry clay into the reclaim bucket.

When bone dry clay comes into contact with water, it sucks it in like a sponge and then slakes down, turning to mush. 

I avoid adding leatherhard pots or partially dried lumps of clay to my reclaim bucket. Since partially dry clay’s pores already contain water, it doesn’t absorb new water and won’t slake down like bone dry clay does. It remains firm and unmixable. 

A mix of wet and dry trimmings are fine because they’re so thin and have a lot of surface area.

 

3. Mix your reclaim bucket

Earlier in this article, I mentioned the importance of water for the reclaim process. If you want the best, highest plasticity clay possible (arguably even better than fresh clay out of the bag) then make sure your reclaim bucket always has plenty of water in it.

You want to keep enough water in your reclaim bucket that there’s always a layer of water sitting on top of the clay. This water does a couple of things. 

One reason is for when you have dry trimmings or scraps and dump them into the bucket, they hit the water and slake down instantly.

But the more important reason is that liquid clay can flow and move and be mixed really well. Mixing is so important because you want all of the particles to be evenly distributed and homogenized throughout your clay body.

Clay is made of different sized clay particles (as we know) plus silica particles and fluxing particles. If your clay isn’t mixed well, you can end up with pockets of flux and no clay, or pockets of large clay particles here and small clay particles there.

All of this can affect both the clay’s working properties and fired results. The better your clay is mixed, the better it will perform. This is not unlike the importance of mixing glazes really well, as described in this blog post.

You essentially want your clay reclaim to be a big bucket of liquid clay slip that you can mix with a drill and paint mixing attachment. The more fluid it is, the better it will be mixed.

And the reason why your reclaim could possibly be better than fresh clay out of the bag is that clay companies don’t tend to mix clay in a liquid state. It would take too much time to remove all the excess water.

They have big, fancy mixing machines and they do what’s called “plastic mixing” where they add just enough water to get the clay to working consistency and mix it in the plastic state. It’s basically like super wedging.

The clay companies do a better job of mixing with their equipment than we can do by wedging, but mixing a liquid will always be more effective than mixing a solid. By definition, liquids can flow and solids can’t.

And since most of us don’t have fancy mixing machines, the better the clay is mixed before we have to wedge it, the easier it will be for us. We have the ability to mix our reclaim really well in a liquid state.

When you’re ready to recycle your clay, the first step is to use your drill and paint mixer attachment to mix it in the bucket. Mix for a few minutes. The longer the better.

Don’t worry if your clay is slightly lumpy, we’ll get rid of those lumps in the next step. But make sure your clay is fluid enough to move and pour out of the bucket. If it’s not, add a bit more water and keep mixing.

 

4. Sieve your reclaim

Wait, what? Seriously?

Yes! I sieve my clay slip just like I would sieve a glaze. I do this for 2 reasons.

Reason #1:

Our fuzzy companions are full of love but they’re also full of FUZZ. And I just can’t handle it when I find black dog hair in my white porcelain.

Sieving my clay removes any hair or bugs or whatever else may have fallen in the bucket over time.

Reason #2:

It makes the clay so nice and smooth, which makes me happy.

You can only sieve your clay if it’s in a liquid state, otherwise it will take forever. Hopefully you added plenty of water during the mixing process.

I usually mix and sieve my clay one day, and then let it sit for at least a day. Once it’s settled, I siphon any excess water from the top before moving onto the next step.

There’s a balance between wet enough to mix well and so much water that it takes forever to dry. I like to add extra water for the mixing/sieving process and then remove as much as I can before the drying process.

 

5. Blocks in the tote 

I take my big Rubbermaid tote that fits my plaster slab and put wooden blocks in the bottom. 

The blocks are to raise the plaster up so there can be a bit of airflow underneath. This helps to speed up the drying process. If there’s a lot of water, the water can drip out of the plaster and we don’t want the plaster sitting in a puddle.

I like using a tote because it’s portable and I can move it around my studio if I need to. I can also put the lid on to slow down the drying process if I need to.

 

6. Plaster slab on the blocks

I put the plaster slab on top of the blocks.

 

7. Make a bedsheet bowl

I then take a piece of an old bedsheet and lay it on the plaster. I use plastic squeeze clamps to clamp the sheet to the sides of the tote. Make sure the sheet lays flat on top of the plaster.

This creates a nice big bowl that I can pour the smooth clay into. Since the clay is so fluid, I don’t have to worry about it leaking over the sides of the plaster. I can add a much thicker layer this way.

 

8. Pour the clay

Pour the liquid clay into the big fabric bowl.

 

9. Wrap clay in bedsheet. Flip until wedge-able.

I carefully remove one clamp at a time and fold the two long sides of the sheet over the clay, and then the ends, wrapping the wet clay up like a present.

Then I let it sit. It usually takes a few weeks to get to wedging consistency in my cold studio. Times will vary depending on your studio environment.

If you want to speed up drying you can put a fan on it. Just keep checking that it’s not drying out too much.

Once the bottom has firmed up a little (still quite soft), I flip the whole thing over and allow it to dry from the other side. I continue to flip it over every now and then. One side is drying from the air and the other side is drying from the plaster.

One thing the sheet is great for is it prevents the edges from drying faster than the middle. The sheet helps to keep the moisture content fairly even.

I’ll often roll the clay in the sheet with my hands, trying to mix the dryer outer layer with the softer clay in the middle.

If I have a dry plaster slab handy and I’m trying to speed things up, I’ll trade the wet slab for the dry. The bedsheet makes it really easy to do this.

You don’t have to have two plaster slabs but if you do it will speed up the process. Or you can do two batches at once. If you’re going to be pouring plaster, I recommend making the most of it and pouring two slabs.

I tend to the clay in these ways, making sure it dries evenly until it’s ready to be wedged. Then I bag it up and it’s ready to go. Nice, smooth, plastic clay, ready to be made into whatever I want.

 

A 9-step clay recycling system

Here’s a recap of my clay recycling system.

  1. Make a plaster slab
  2. What to put in your reclaim bucket
  3. Mix your reclaim bucket
  4. Sieve your reclaim
  5. Blocks in the tote
  6. Plaster slab on the blocks
  7. Make a bedsheet bowl
  8. Pour the clay
  9. Wrap clay in bedsheet. Flip until wedge-able.

I hope this either helps you improve your recycled clay or motivates you to tackle those reclaim buckets that you’ve been neglecting in your studio. We’ve all been there! Having a good system makes it easy.

Do you have any clay recycling tips to share? Post them in the comments below. 

 

Join my free community

If you love learning about and discussing glazes, I’d like to invite you to my free social learning Facebook group called Understanding Glazes with Sue. The group is full of videos and discussions about firing, mixing glazes and fixing various glaze issues. Please join!

 

 

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