A very fine-grained plastic clay of volcanic origin containing colloidal matter. Used in small amounts as an additive to clays to aid in plasticity and in glazes as a suspending and binding agent.
Vee Gum-T - A macaloid-type Bentonite suspension agent for glazes. Also used as a surface hardener. It is an extremely plastic, hydrous magnesium silicate used to give plasticity to non-plastic whiteware and refractory bodies. Very similar toMacaloid.
Melting point approx. 2192°F
Bentonite can be added to most glazes in amounts up to 1%. Excessive amounts can cause a glaze to become gel like. When used as a plasticizer in clay body, 1-3% is generally used. Bentonite can cause warping and cracking in clays if used in large amounts.
Bentonite should always be added to dry compositions, never to wet. Magnesium bentonites tend to swell, holding large amounts of water. Calcium bentonites are of the non-swelling variety.