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This is 50g of sodium bentonite in 1 gallon of water (~0.5% concentration). Sodium bentonite can swell up to 10–15 times its dry volume, creating a thixotropic gel that really resists mixing. With a better propeller, faster mixer, hot water, slow addition, etc. we might be able to achieve 1% (or ~100g/gallon). Apparently, with industrial high-energy mixing in special vessels, 4% is possible for drilling muds. They can even go beyond that using shear pumps, ribbon blenders, or paddle mixers to achieve a pseudo-plastic non-Newtonian gel. 4% - that seems impossible to me! Why does all this matter? Some say that a gel like this can be added to a settling glaze to fix it. Is that true? Not really. Here is why. Our typical imperial gallon of dipping glaze contains 3500g powder (US gallon 2800g). At least 1% bentonite is needed to make any difference, that is 28-35g. If you have a great mixer and can make a slurry having double the concentration of this one, 100g/gallon, then to deliver the minimum bentonite for a gallon of the glaze would require 1/3 gallon of this! While the added bentonite might help somewhat, the effects of all that extra water will cancel the benefits.
Troubles |
Glaze Slurry is Difficult to Use or Settling
Understanding glaze slurry rheology is the key to solving problems and creating a suspension that does not settle out, applies well, dries crack free. |
Troubles |
Powdering, Cracking and Settling Glazes
Powdering and dusting glazes are difficult and a dust hazard. Shrinking and cracking glazes fall off and crawl. The cause is the wrong amount or type of clay. |
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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