Minnesota Clay Co. USA Technical Info - Recycling Clay

Whether you are a studio artist or an art educator, at some time you have to face the job of recycling or mixing your clay. Mixing or recycling clay by hand is a fairly simple process but it also can be: physically demanding, take up a fair amount of studio space and it requires keen attention to protecting yourself from the hazards of airborne dusts and flying bits of clay, etc... The same personal protection issues pertain to mixing with the assistance of mixers and pugmills. You need appropriate ventilation, masks and eye protection for working with powdered or dry clay materials.

D.I.Y. = The Cheap Method

The following is a minimally dusty method to recycle clay trimmings and other clay scrap. (This does not mean that you can skimp on safety devices, put that mask back on!) While your clay scrap is still moist, roll it into thumb thickness coils and place it on a tray to dry. Remove the tray from your studio area (like a garage), or place it in an area that has very little air movement. The key is not to create an exposure to the finest clay dusts - they are the ones most readily moved into room air and these dusts are the most hazardous to your lungs. When the clay is absolutely dry, carefully place the coils into a heavy clay bag (3 mil. or thicker), and break the clay coils into small pieces with a mallet.

Again, we’re trying to keep dust to a minimum here, so it’s best to wear all the safety devices mentioned, provide adequate ventilation to remove fugitive dusts. This is an operation that can also be performed outside.

Now, fill a 5 gallon bucket half full of water. Pour the crushed clay into the water approximately 5 pounds per 15 minutes. Layering in this way will allow the clay chunks to saturate with water before they are submerged under another layer of dry clay pieces. Continue this layering until the bucket is half full of clay.

After 4 days there will be a layer of clear water on top of the bucket. Decant as much of this water as possible from the bucket. Now, you will need to have a plaster tray prepared on which to spread out the clay slurry. A framed window screen with canvas laid across it will also function as a suitable tray. Unload the wet slurry on to your tray to a thickness of about 2 inches (5cm). If you notice chunks of hard clay during this process, they should be set aside and sent through the process from the start again. Also, be cautious when unloading the slurry, sometimes sharp tools can make into reclaimed clay and finding them with a bare hand can really ruin your day!

Monitor the drying process over the next two days. Remove the clay from the trays slightly damper than you normally use it. Wedging will cause the clay to stiffen slightly. Store reclaimed clay in heavy weight plastic bags.

Hand Mixing from Scratch

Hand mixing from scratch follows the reclaiming process fairly closely but you start with already dry powdered constituent materials. The trick is getting the dry powder materials blended without raising a lot of dust. I have seen dry clay blended outside in a kiln yard using hoes, rakes and other farm implements. This is messy and of course a respiratory hazard. (Anyone recognize a theme here?) Dry materials can be sealed in a large bag and massaged about in an effort to blend the materials, but you will be limited by how much clay you’re physically capable of wrestling with! If you have a ball mill, the dry materials can be loaded into a large container, sealed and placed on the mill to turn...

By now you’ve decided to get some mixing equipment.

Rule number 1: Do not buy a pugmill when you need a mixer! Most pugmills do not mix clay effectively, they perform other very beneficial operations; most notably they compress and they can de-air the clay. The augers in a pugmill perform very little in the way of a mixing action. Augers move the clay forward through a shredder, some models then provide a de-airing vacuum chamber and finally through a nozzle opening.

Mixers, on the other hand continuously work the clay, distributing water throughout the mixture until the clay is one homogenous, moist consistency. Clay that is completely mixed is then either wedged or then sent through a pugmill.

Selecting Mixing Equipment

There are a number of manufacturers of studio quality equipment. Among the more popular brands are Peter Pugger, Soldner and Shimpo. Each has excellent safety features and this should be number 1 in your evaluation criteria. Check the specifications: mixers are often rated by the total batch weight the machine can handle, and pugmills are measured in the amount of clay they can process in an hour. Evaluate your studio’s clay use: a smaller capacity mixer or pugmill will cost somewhat less than larger machines, but will require a greater investment of time and energy.

A de-airing pugmill is more likely to allow the user to use the clay without wedging right away, but most non-deairing pugmills will provide a dense extrusion that requires only minimal wedging.

No matter which method you use, keep in mind that clay is a wonderful material because it never needs to go to waste.

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