For glaze and clay body mixing, bentonite refers to sodium bentonite. Retailers often sell sodium bentonite as just "bentonite".
Bentonite is an extremely plastic clay. Glazes usually use 10-30% kaolin to suspend the other ingredients, but a glaze with no other clay can be suspended with only 1-2% bentonite.
Bentonite is hard to add to ceramic slurries because it gums and does not wet. These are precisely the properties we are using bentonite for, so we can't add bentonite like other materials.
If you have a power drill or blender, you can use electricity to disperse the bentonite. Add the water and other dry materials and add to a bucket or blender. Turn the drill or blender on and at a speed where the water forms a vortex. Slowly add the bentonite into the vortex (adding too much will create clumps). Drill or blend until all clumps disappear.
If drills or blenders are not viable, you can get most of the way there by dry mixing the bentonite. Add bentonite and all other powder to a sealed container and shake vigorously. Be careful when opening as this will generate a lot of fine dust particles. As always, when handling dry materials, you should wear a mask.
Because bentonite is so plastic and sticky, it can be hard to process. When I mix my clay bodies (Slurry Mixing Clay Bodies), I use a drill mixer and drill on high speed until all the bentonite clumps disappear.
John Tilton's notes on mixing porcelain say to power mix bentonite for 2 hours. This may be necessary for him to get the most plasticity out of his bentonite.
Plasticity from kaolin + bentonite feels rather different from a ball clay's plasticity. A porcelain with only kaolin and bentonite as clays can feel rubbery and stiff. It will also ball up when trimming rather than forming ribbons.
1-2% can suspend glazes that are low in clay.
Synthetic bentonites are attractive for Porcelain Formulation because of their purity and extremely high plasticity. I plan on mixing a porcelain clay with Laponite.
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