Question: Can you use bentonite instead of Epsom salt for hard panning?

Dealing with hard-panning

In my free Strategic Glazing class, I talk about flocculation. Flocculation is a way of increasing a glaze’s viscosity without adjusting the specific gravity and without changing the water content.

If you have a glaze that’s hard panning, where your glaze is having trouble staying suspended in the bucket, then one solution for that is to flocculate your glaze, because sometimes the materials that are in our glaze recipes will have a deflocculating effect that causes glazes to settle. 

But bentonite also helps to keep our glazes suspended, so the question is – can you just add bentonite instead of flocculating to deal with a glaze that is having trouble staying suspended in the bucket? The answer is – it depends! 

I always like to fix a glaze recipe if I can first, but before I make changes to the bucket, like flocculating, to solve a suspension problem. So I would rather add clay to my glaze recipe in the form of bentonite to help with suspension problems, if the recipe is low in clay and doesn’t already contain 2% bentonite.

Check glaze recipe for clay and/or bentonite

So the first thing I do if I have a glaze that’s hard panning is to look at the recipe and check the clay content. If it’s really low in clay content, then I’m checking if there’s already bentonite added? If there’s low clay and no bentonite, then that would be the first step that I would take. I would add 1-2% bentonite to the glaze recipe and see if that helps keep the glaze in suspension.

Flocculate if clay content seems sufficient

If the glaze already has plenty of clay and/or bentonite and it’s still having trouble staying suspended, then that’s an indication to me that there’s an ingredient in the glaze that is causing it to be deflocculated. And sometimes the deflocculating of clay particles causes them to lose their suspending properties and they can really struggle to keep the glaze suspended in the bucket.

In that case, if my glaze has sufficient clay and it already contains bentonite, then I would look to flocculating the glaze to help with suspension problems rather than just adding more and more bentonite.

So there are different reasons why I would choose bentonite vs flocculation. If there wasn’t already bentonite in the glaze recipe and it was having trouble staying suspended, then I would use bentonite. If there was already bentonite, then I would turn to flocculation.

Check for calcined kaolin

And another thing to check for is if your recipe contains calcined kaolin. That’s kaolin that has been fired to a temperature to drive off the chemically bound water molecules. That could also be preventing the glaze from staying in suspension, if you have too much calcined kaolin and not enough kaolin. So you could add bentonite to an existing batch, and then you could replace some of the calcined kaolin with un-calcined kaolin for future batches. Both of those things would help with keeping your glaze suspended in the bucket.

It really depends on the glaze that you’re working with, what the right strategy would be. Sometimes we have calcined kaolin for other reasons. So you could either add bentonite or you could replace some calcined kaolin with un-calcined kaolin.

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