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Glaze Settling Out - What To Add?


Celia UK

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So, my next problem - in need of your help.

I have tried to get my head round the issue of flocculation and Deflocculation several times but still can't quite get it! Right now, the theory isn't exactly what I need, it's urgent, practical advice.

 

I've just mixed up 2 litres of a bought, lead free, transparent stoneware glaze (fires 1180oC - 1250oC).

1 kg : 800mls water. It immediately settles out and will need to be stirred every few minutes to keep everything mixed. What is it I need to add to keep the ingredients in suspension? I have Epson Salts, Dispex, CMC gum and some Bentonite. So, firstly, what to add to this batch and then, if mixing another batch, should I add something at the dry materials stage?

 

Thanks in anticipation!

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I add 1% epsom salts and 1% bentonite.

 

Bentonite can gell so its best to mix it with the dry or with some water before you add it in.

 

Here is a topic that talks about it a little http://community.ceramicartsdaily.org/topic/5727-a-few-glaze-problems-drying-to-slow-not-enough-suspension/?hl=%2Bglaze+%2Bsuspension

 

 

Add 2-3% bentonite and 0.5-1% epsom salts.

 
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Guest JBaymore

1% bentonite is a pretty "standard" addition to almost any glaze that you mix yourself to deal with both suspension and "dusting" issues.  It can go up to about 2% if there are still issues without changing much about the fired qualities of the glaze. 

 

Hard to add dry bentonite to a wet glaze. The clumps of gel it forms in water is hard to break up.  Use boiling water to dissolve it into slowly ..and then add the thick smooth gel mess into the wet glaze and then sieve the crap out of it. 

 

CMC will also affect the settling a bit and also will greatly help the application qualities and also the dusting.

 

Water chemistry is different all over... so Epsom salts need to be added slowly to a batch on a case-by-case basis.  Add some, check the suspension / viscosity then add a little more.  And so on.

 

Epsom salts works mainly on the 'plastics' (clay particles) in the slurry... so first you have to HAVE some for it to impact.  SO if the glaze is deficient in clay... add bentonite before adding Epsom salts to the water.

 

best,

 

..................john

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I used to use epsom salts in every glaze I had. I kept a lidded container of water with as much Epsom salts in it as would dissolve. Every time I made a new glaze I would add 2Tbsp of this liquid to the glaze liquid, helped to keep glazes from settling or worse yet hard panning. If I had a glaze that settled out quickly, the next time I made it up I would add bentonite before mixing in water. When mixing up 15 glazes for HS studio, you get to learn your glazes pretty well after a year of so. Back then, I would look at the recipe and take interest in how much clay was involved in the formula, and how the glaze settled after mixing. Now I am more aware, and using Insight for more understanding of the glaze chemistry.

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Over on this side of the pond there is the regular bentonite plus a white firing one. The regular one can leave tiny specks in a transparent glaze. Don't know if specks are an issue with your transparent glaze. (macaloid and veegum don't leave specks, you use about 1/2 the amount of those as you would use of bentonite)

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Marcia, John, Pres and Min - Thank you all! I can now proceed to add some epson salts with more confidence and next time, I'll add bentonite to the dry glaze. Min - thank you for the word of warning, I think I'll try a sample before mixing a large qty, to check it for speckles!

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