What could cause this (hard panning)

[Morgan]

I am using a glaze I’ve used for months now, have many variations of it that I have been using for well over a year and never had any suspension issues…until today the strangest thing happened.

i glaze about every two weeks so that’s about how long these sit if not longer. Anyway I pull out the glaze in question, mix totally fine do my glazing go eat lunch and come back and go back to same glaze and it’s hard as a rock all the span of maybe an hour. The glaze has very little clay and I add 3% bentonite to these but I’ve never ever had issues with it, even after sitting for much longer time. The quickness that it happened is what threw me.

the only thing I can possible think of was that it got warm as the sun may have hit the bucket? The glaze in question does have soluble ingredients so maybe heat interacted with it?

[PeterH]

Do you have a recipe (typical or "base" if you have many variants).

What are the soluble ingredients?

Do you dip or brush, and what volume of glaze are we talking about.

Your wording suggests that all the glaze solidifies, but you title says hard-panning which I associate with a thinnish hard layer at the bottom of a liquid.

[Morgan]

Apologies, I should have included that but was on my phone. I do know that huge amounts of Neph Sy can change over time solubility, so maybe that is why, but still seems strange it has yet to happen to any other variants much "older" than the one that showed this behavior (and again, happened within an hour). This was a 4k batch all have 3% bentonite to prevent whats happening. I will probably add some epsom salt today (or more bent?) to try and fix it, but I am curious as to the why and why now more than anything.

As for the Hard Panning there was some water on top and the bottom had hardened to the point where a mixer would not budge in it, I had to loosen it up by hand and I finally got it back to normal. Update: Checked it this morning and it was already starting to happen again but not nearly the rate at which I saw yesterday. 

The strangest part of this to me is how it was 100% fine out of storage a few weeks and not until I starting using it did this kick off the issue almost immediatly.

This is the popular micro crystal recipe base "Frosty". 

Nepheline syenite 40.00  
silica 29.00  
zinc oxide 17.00  
whiting 9.50  
EPK 5.00

total base recipe 100.50 

bentonite 3.00 
rutile 2.00

 

Edited November 2, 2023 by Morgan

[PeterH]

I'll leave it to the experts after mentioning this high nepheline syenite glaze previously posted, which uses a particular suspension agent.
 

 

PS

Glaze additives: https://clayworkssupplies.com/wp-content/uploads/2022/03/Glaze-Suspenders-and-Additives.pdf

[Morgan]

Yes, I realize this is a prone glaze given the ingredients, which is why there is agents added to account for that. I think this is a bit more specific of a question of what would cause, an already well suspended glaze, out of nowhere to start to exhibit this behavior in such a short time frame after no issues for some time. Besides simply adding more bent/epsom etc I am trying to understand what could have changed that is causing this to avoid it down the line.

[PeterH]

That's what I hope the experts will explain. I was just pointing out the use of a specific suspension agent for another glaze very high in  nepheline syenite.

[Babs]

How long since you mixed the batch?

Did you check the Spec gravity?

No expert here but if you haven't had hard panning with these ingredients you're lucky.

No expert, but I kmow that after a time the effort you've gone to to defloc or floc will need revisiting  because the chemical reaction needs a boost.

Heat will accelerate certain chemicsl reactions but not an expert just an observer.

[Dick White]

What @PeterH said. Neph sye is a known bad boy in the glaze chem world. It is very high in sodium, which is why it is popular. It is also slightly soluble. Sodium is an alkaline deflocculant, which results in hard panning. The sodium slowly leaches out of the neph sye and at some indeterminate point deflocs the glaze slurry and it hard pans.

Also understand clay is the only material that can be flocculated to create a suspended glaze slurry. Materials such as feldspars or feldspathic materials (neph sye), other minerals such as whiting, etc., or frits do not respond to the alkaline or acidic conditions in the slurry to deflocculate or flocculate, respectively. Only clay responds to the deflocculation/flocculation process. A recipe with little or no clay, such as your recipe with a mere 5% EPK, needs a few additional percent of bentonite (a super clay) upon which to cause flocculation (if needed) by adding a mild acid such as epsom salts. And then after some time, the alkaline sodium leaches out of the neph sye and neutralizes whatever acidity in the slurry has been keeping the clay suspended, and boom, without warning it all falls down. The bentonite is not enough to stop this from happening. Dig it out and remix it with some epsom salts or vinegar to neutralize the excess alkalinity and restore the suspension.

As for the Magma product that folks above recommend, it does not chemically flocculate the slurry. It is an artificial gum additive that mechanically suspends the glaze solids. It is unaffected by the soluble leached sodium from the neph sye. It also has other attributes, so read the cautionary statements on the label. Otherwise, it floats bricks.

 

[Morgan]

Awesome Dick and everyone else, that was what I suspected, so much appreciate the detailed response. I added an extra percent of Bent to 3% and my other variants of this same base glaze have not had this happen and they are much much older (some a year old no issues just 3% bent), this is a newer addition with simply a touch of copper carb to it. Anywho, I will add epsom salts as needed. 

Babs, it had been at least 2-3 weeks since I mixed the batch and the initial mix after sitting was totally fine. Glazed quite a few things, came back an hour later, and boom this happened. 

Edited November 2, 2023 by Morgan

[Min]

I'm not going to comment on the durability of this glaze but I did rework it to contain nearly double the epk and got rid of the nepsy and supplied what it did with a frit plus Minspar. Should suspend a lot better with less bentonite needed (if any at all). If you try it Morgan please just test a small amount first, what looks good on paper and all that.

edit: if you test this and find it's too fluid (because of the frit plus tiny bit of boron) then it might need an extra 1 or 2% of EPK

Edited November 3, 2023 by Min

[Babs]

I'd be stirring your glaze every couple of pots if dipping, you'll find the copper at least, at the bottom of your bucket otherwise.

What Dick said 10x,  nephsy sets like a rock in that recipe, crusts in the inside of bucket. Why suddenly? Hmmm, because it could, murphy, showing who's boss, that's ceramics for you!

[Babs]

Better shorten your lubch break:-)

[PeterH]

I wonder if the amount of clay in the glaze influences the number of sodium ions needed to change the pH by a given amount?

If so the level of deflocculation will change faster the less clay there is about to "buffer" the pH -- as the rate of leaching of sodium ions from the nepheline syenite is presumably hardly  influenced by the amount of clay about.

[Morgan]

5 hours ago, Babs said:

I'd be stirring your glaze every couple of pots if dipping, you'll find the copper at least, at the bottom of your bucket otherwise.

What Dick said 10x,  nephsy sets like a rock in that recipe, crusts in the inside of bucket. Why suddenly? Hmmm, because it could, murphy, showing who's boss, that's ceramics for you!

It gets stirred every pot haha with a rush to dip, tongs in one hand and mixer in the other 

Thanks for the rework min. This is not meant to be a durable glaze it only goes on exteriors and for me, up until this fun little adventure/lesson, has been a pretty decent micro crystalline glaze that doesn't run and works well within my normal firing with natural cool. That said, I will certainly give that a test, thanks!

[Morgan]

20 hours ago, PeterH said:

I wonder if the amount of clay in the glaze influences the number of sodium ions needed to change the pH by a given amount?

If so the level of deflocculation will change faster the less clay there is about to "buffer" the pH -- as the rate of leaching of sodium ions from the nepheline syenite is presumably hardly  influenced by the amount of clay about.

Interesting for sure. I am also curious how heat affected suspension/sodium etc. After mulling it over I am convinced the bucket sitting in the hot sun for an hour was in fact the variable that somehow changed the solution super quick and thus this happened. Anyway, epsom added and resolved but still curious to what really happened from a scientific point.

[PeterH]

Certainly temperature has an effect. And I think that a small amount of clay will deflocculate faster than a larger amount would (as it needs fewer sodium ions to do so).

Flambe magic (John Britt's experience of crystal forming in glazes through thermal cycling)
http://ceramicstoday.glazy.org/articles/flambe_magic.html

Deflocculation
https://cawstudiopotters.wordpress.com/deflocculation/

[Morgan]

Great articles ^^ cheers!

[PeterH]

Pure speculation.

As pH meters are so cheap (while presumably still functional) might it be worthwhile monitoring the pH of "unstable" glazes with slightly soluble components. Hoping it gives an early clue about when magnesium additions are required.

e.g. Digital pH Tester Pen Water Pool Hydroponics Drinking LCD Test Pocket Electric
https://tinyurl.com/4pd8wn4m

PS I've no idea what range of pH covers the flocculation process. The buffering effect of the clay could make is very small.

Edited November 5, 2023 by PeterH