Left: A small dry lump has been immersed in water (top is a sodium bentonite from Saskatchewan, bottom is a calcium bentonite from Mexico). Right: After ten minutes both have swelled. Although the character of the swelling is a little different, both dewater on a plaster table and exhibit similar plasticity. Both create a gelled slurry having similar feel and character. This seems odd. The lesson appears to be that all sodium bentonites are not created equal. Sodium bentonites normally resist wetting, they literally cannot be stirred into water without the use of high-energy mixing equipment. And tiny amounts can gel a large amount of water or plasticize an otherwise short clay body. However, that is not the case with this sodium bentonite we are getting from Saskatchewan. This is exciting for us because it suggests that this material, although not plastic enough for use in ceramics, can be used for cosmetics, masks and detox.
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.