Supercharge the plasticity of reclaimed clay using bentonite

If your reclaim is short (non-plastic) restore it by mixing in some bentonite - as little as 2 parts per 100 scrap (in dry form) is often plenty. Note however that bentonite is hyperplastic and won’t mix with water as a pure material. The preferred method is thus to dry out the scrap, crush it as much as possible, then mix in the bentonite as thoroughly as possible. Finally, slake it, propeller mix as a slurry, sieve if needed and then dewater on a plaster table.
In a wet climate, the previous method might not be practical. An alternative is to make a 50:50 ball clay:bentonite powder mix, as demonstrated in the video. Thoroughly shake them together in a plastic bag (to separate the super-tiny bentonite particles), slurry it up and dewater to plastic form for wedging into plastic reclaim. There are issues, however. If the bentonite is high in soluble salts the slurry can leave a scum on your plaster batt (fixable using a sandscreen). Blender mixing is best but will demand much more water than typical body mixes. A third option is the use of pure ball clay, but 5-10% might be needed. Ball clay can be blender mixed using much less water but it will still take a long time to dewater and is super sticky in plastic form. And the percentage needed will likely impact body fired maturity, making it fire a little more porous.

Related Pictures

These are behind the art center. A dirty secret. Or an opportunity!

Barrels of scrap clay behind the art center

When many clays are in use there is good reason to collect like this - you will see why in a moment. Each barrel is a unique product, a mix of random clays used by students. Each could be thus considered a wild clay, inconsistent throughout and with impurities. As such, each needs to be characterized, as a whole. For example, consider the front barrel: What does it look like when fired at various temperatures? At what temperature does it mature? What is the drying shrinkage and how plastic is it? Does it fit the glazes we use? This information not only describes the clay but also points to what needs to be added to make it useful (e.g. bentonite or feldspar). An account at Insight-Live.com is a way to organize the testing and post the results to a group (the SHAB test, for example, is perfect to describe the plastic, drying and firing properties). Once the clay in a barrel becomes predictable then it becomes useful.
To do the testing it is necessary to get a representative sample from each barrel. The method depends on how processing will be done. In a wet climate, the wet contents are likely to be thrown into a pugmill (with impurities), recycled until mixed and then bagged - a sample can be taken when complete. But the dry climate option is much better: Dewater each barrel, do quartering to get a representative sample and then characterize it. Finally, slake, slurry up batches using a propeller mixer, screen in a vibrating sieve and then dewater (e.g. on a plaster table).

Links

Articles	Recylcing Scrap Clay Guidelines for collecting, reprocessing, testing and adjusting scrap recycle clay in a pottery or ceramics studio or production facility.

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