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dhPotter

Bentonite - When To Use It

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Should or Can Bentonite be used in every glaze recipe? I have been mixing glaze tests this week. Some are mine that I formulated some are from CM and other articles.

 

The glazes formulated by those who know much more than I do about such use 1-2% Bentonite. What do the fine folks here have to say about the use of Bentonite?

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Kind of depends on the glaze, glazes with lots of clay in them tend to not hardpan.  Bentonite is typically used to aid in glaze suspension. At 1-2% there is enough to help suspension, but not enough to mess with the glaze.

 

I don't always add bentonite, but I DO always add CMC gum solution to my glazes.  It helps with suspension, flow off the brush/brushability, and more importantly it forms a "hard coating" that keeps the glaze from rubbing off in greenware state.

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I don't generally use bentonite.  It's sometimes annoying to mix, and since all of my glazes have healthy amounts of clay in them, I don't seem to miss it much.  The only glaze I have that hardpans is a high iron red.

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If the glaze has 10% or more clay in it you shouldn't need bentonite. If you do use it, you have to dry mix it with the other ingredients before adding water. If you don't it will clump up into a sticky glob. It's also a good idea to use epsom salts with it, approximately 0.5% by dry weight.

 

I don't recommend using CMC gum in dipping glazes because it will increase the water content of the glaze, which causes over-saturation of the pot and increases drying time. It's great for brushing formulas, though.

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I like adding bentonite (1-2%) to my glazes. Nearly all of them have it.

 

The small amount of bentonite will also make the dry glaze more durable. If you are having trouble with glazes chipping or flaking when being handled, consider adding it.

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