It took weeks, in our dry climate, for this small sample to dry. It is pretty much impossible to slurry up and dewater this clay in the normal way. So to make the thick gel on the left I blender-mixed a slurry as thick as I could make it and then let it sit to evaporate the water. By the time it was non-sticky enough to handle it was too stiff to shape. To test bentonites, it is thus necessary to mix them with a non-plastic powder (e.g. silica), usually at 90% or more. However, we have a better way: Roast or calcine some of the betonite powder to destroy the plasticity and mix that with the raw (usually 85% calcine and 15% raw).

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Only a small addition of this material, often 1–5%, can dramatically increase the plasticity and dry strength of a porcelain or other clay body. Why not use one of the very white specialty plasticizers instead? Cost: they can be ten or even twenty times more expensive.
This is a typical Wyoming bentonite. It is so plastic that, to make these SHAB test bars without excessive drying cracks and warping, we mixed it 90:10 raw and calcined powders. These fired bars, cone 1 through 7 oxidation (bottom to top), reveal the baggage that comes with that plasticity. The material is iron-bearing and fires progressively from reddish brown to very dark brown as vitrification advances. At the higher temperatures, the surface becomes strongly glassy (because of the soluble salts it also contains). Yet, at an addition of only a few percent, its contribution of iron and other impurities to the total body is small enough that the loss of whiteness can be surprisingly modest. That is why an inexpensive, decidedly non-white bentonite can still be a very practical porcelain plasticizer.
| Materials |
Bentonite
Bentonite can make a clay body instantly plastic, only 2-3% can have a big effect. It also suspends slurries so they don't settle out and slows down drying. |
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