| From the pages of Pottery Making Illustrated
In the Mix: What's the Slurry? by Jonathan Kaplan
Clay Recycling
The work we make generates discarded clay—scraps from trimming and slop
from throwing or handbuilding. Whether you make your own or buy
prepared clay, you need to decide what to do with used clay. For some,
the solution is to throw the scraps in the dumpster and dump the slop
down the drain, which isn’t really a solution. It’s economically and
environmentally wasteful and can wreak havoc on your plumbing, sewer
and septic systems.
All discarded clay—except that which comes in contact with plaster or
other contaminants—is recyclable and reusable. Reclaiming it requires
planning a system for your particular studio situation. Although
there’s no one way that works for everyone, some basic guidelines can
make this job easier.
The following solutions, submitted in a recent PMI reader’s online survey on clay reprocessing will give you a place to start.
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Collecting and Storing
- A trash container of some sort is the key to any system. Placed on wheels, it can be maneuvered anywhere in your studio. Remember that when filled with clay scrap, slop and trimmings, it will be very heavy, so buy a heavy-duty container, and use heavy-duty casters for the dollie. Pouring the scrap clay through a framed screen that sits on top of the container breaks up the scraps into smaller pieces and catches tools that got lost (figure 1).
- When you’re done with a day’s work, dump your throwing slop and any scraps into the bucket. If you plan to recycle scraps that have fallen on the floor around your wheel, make sure there’s no non-clay debris on the floor first, otherwise you should simply throw these scraps away as the foreign matter could cause problems. Rather than using a broom, use a metal dustpan and your hands to collect the clay.
- As the bucket approaches the top, decant the water. As long as there is water over the layer of clay in your recycle bucket, the clay scraps will all break down and become thoroughly saturated. If there are lumps or dry material in the slop, the resulting reclaim will have hard and soft spots. You don’t have to mix the clay in the bucket with a mixer. Let the water do its job.
Reclaiming
- The resulting very wet scrap usually needs to be dried out before reprocessing can continue. Here’s a list of the more commonly mentioned and used methods.
- Spread a thin layer (2-inches or so thick at most) of scrap onto an absorbent surface (figure 2). Plaster bats, wedging tables and large plaster slabs are good choices for this. A material called HardiBacker Board works very well. This is a heavy cement board that is not as effective as plaster, but is strong and will absorb moisture from the clay. Caution: do not use sheetrock. This is thin and porous, absorbs water very quickly, then the paper delaminates from the surface and the boards weaken. Flip the clay slab over periodically (it should pull away from the surface easily when it is ready to flip) and continue to do this until it is right for wedging.
- Store drying bats on a vertical rack or ware cart to save space. Note: the HardiBacker boards need a board underneath for support. Some potters prefer to dry their reclaim outdoors. Note: cover the reclaim with a sheet or other breathable fabric if you live in a windy area to prevent foreign materials from getting in your clay. A fan can also help dry wet clay more quickly. This will accelerate the drying, so turn the clay frequently.
- Another practical method involves a rudimentary filter press system made from cotton pillowcases. Simply fill the sacks with clay slop and hang them up, either over a bucket or outside. Excess water eventually drips out over time and evaporates from the surface.
Reprocessing
- When adding reclaim that has already been through one of the above processes to the clay mixer, make sure you mix the water and the dry clay first before adding the reclaim. Alternately, add the slaked-down reclaim straight from the bucket to the mixer (without drying it out first). This works best if you’re mixing a large batch of clay (over 100 pounds). Put the reclaim in first and add dry ingredients in small batches on top of the reclaim, adding water as needed to maintain the right consistency. A ratio of 2/3 dry materials to 1/3 reclaim usually works well.
- Once your reclaimed clay has achieved the consistency you want, block it, bag it and leave it alone for a few days to let the moisture content even out. It can then be cut into small pieces or thin slices and re-wedged with your boxed clay or used as is.
- A common misconception with a pug mill is that you can combine dry mix and wet mix successfully and get a decent extruded pug. Not true. Although the dry mix sets up the wet mix in the machine, the dry mix itself will not be suitably hydrated and, as a result, the clay will be exceedingly short. If you prepare your clay this way, do so well in advance of using it; bag the clay, let it age, and it will fully hydrate over time. The same is true if you are wedging dry clay into very wet wheelthrown clay to make it workable again.
- All plastic bags have a degree of porosity, and release moisture or let in air over time. Mix clay and reprocess scrap just a bit on the wet side to allow for a small degree of air infiltration through the plastic bag.
- Finally, don’t let the volume of reclaim get out of control. If you keep up with it on a daily basis, you’ll always have reclaimed clay ready to go, and not have an overflowing bucket of scrap. And, if you’re just overwhelmed and don’t have the time, space or inclination to delve into clay recycling, consider donating your unwanted clay to a local school or art center.
Jonathan Kaplan is a frequent contributor to PMI. He has been actively involved in the ceramics field for 40 years. He lives in Denver, Colorado, where he curates Plinth Gallery. He can be contacted through www.jonathankaplanceramics.com. |
| Figure 1: A screen over the scrap clay barrel not only keeps out tools and sponges, but also the dreaded needle tools.
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| Figure 2: Place recycled clay on a porous surface and allow to dry. Flip the clay over occasionally then wedge and store.
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