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  1. As part of my ongoing clay body development project I have been looking again recently at bentonites. I have access to a source of calcium bentonite and wanted to find out if others have used it any of their clay bodies, what their experiences were, etc.. Most of the discussion around bentonites seems to be around the hyper-swelling sodium bentonite (Wyoming) and the plasticity benefits it brings. What little research I have been able to find suggests that calcium bentonite swells when hydrated, too, but only about a fifth as much. If calcium bentonite even gets a mention in the context of ceramics, it is almost inevitably about how it can be chemically converted into sodium type via a cation exchange process (sodium bath). But what about using calcium bentonite as a more substantial addition to a clay body? Even though it doesn't swell like sodium bentonite, its does swell some, and its potential to add plasticity still seems much higher than most other alumina-silicate materials in a clay body (eg, china clay or stoneware clays). While most people would only ever add a few % of sodium bentonite to a clay body (more than this it becomes sticky and harder to work with?), in principle you could add several (5?) times that amount of calcium bentonite. Perhaps some wou Setting swelling capacity aside, bentonites (including calcium bentonite) in general have a small particle size which in theory could/should improve the green packing density of the clay body. Apparently calcium bentonite is often used in foundrys for its combination of plasticity and favourable green strength compared to sodium bentonite. Calcium bentonite might also have a helpful chemistry (or not!) for the clay body, which starts to become relevant when you are adding potentially 10% or 12% rather than 2% or 3% as a raw material. I am one of those people who thinks that clay body chemistry DOES matter, particularly when you are want to ensure the body is functional. I guess color and impurities of the bentonite would have to be taken into account the more you add, not unlike a ball clay in this respect. Similarly, perhaps calcium bentonite could replace a portion of the ball clay addition under certain circumstances. I also suppose that the cation exchange capacity of bentonites becomes relevant in the context of the other raw materials in the clay body (eg, sodium, Nerd?) the more that you add. Interested in any thoughts or experiences anyone has. Also interested in any bentonite specific research anyone has run across.
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