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Problems With Clumping In Glaze


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#1 Mark Horst

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Posted 24 December 2010 - 03:38 PM

I'm having some trouble with one of my glazes clumping. It is not a settling problem because it mixes back up fine, but with the exception of pebble sized clumps of something. I'm assuming it's silica because once fired the places where these clumps end up are clear and don't have any color. It's like little pebble sized clumps that feel like sand when I rub them between my fingers. In the past I've sieved the chunks out, but am worried that I'm tampering with the formula... here's the formula:

Hirsh Satin Matte Blue
9 Lithium Carb.
35 Fint
32 Gerstley Borate
4 Neph Sy
4 EPK
17 Whiting
2 Bentonite
1.5 Copper Carb.

It's a cone 04-02 glaze... any thoughts would be helpful. Oh, and it hasn't frozen, so I'm sure it's not that. Also, it seems to start happening about 4 months after it is originally mixed up.
Thanks,
Mark

#2 icyone

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Posted 26 December 2010 - 04:45 PM

It's some weird thing called oolites I think it's like calcium deposits. Happens more supposedly in warmer areas of my studio.

When ever I get them I run all my glaze through my talisman filter.

It happens on me if the glaze sits a while, even happens after it's been filtered if it has been a while

#3 Ben

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Posted 29 December 2010 - 09:39 AM

What you have here is a solubility issue. Both Lithium and GB are soluble to a certain degree. These solubles can combine to form crystals. Think "rock candy". You can either sieve out and grind up the crystals, then return them to the batch each time you want to glaze a run of pots OR reformulate the glaze.

If you want to eliminate these crystals you'll have to reformulate the glaze to eliminate some or all of the solubles. Lets look at the formula. I rearranged the ingredients to group the solubles together. I'd say you can ignore the flint~copper carb and concentrate on the other 3 which are all soluble.

32 Gerstley Borate
9 Lithium Carb.
4 Neph Sy

GB supplies boron and much has been written about replacing it with various engineered substitutes and frits. see http://digitalfire.c...rate/index.html
Lithium can be replaced by spudumene but it isn't a 1:1 deal. You'd have to calculate and test to see if it works.
It may be possible to completely replace the Neph sy in the process of replacing these other 2.

I'd start with replacing the Lithium and Neph sy since they only add up to 13 parts of the recipe and see what it looks like. If it fires the same, keep it around for a while and see if it makes clumps.


I'd be glad to help with the recalculations if you want to test them.

Ben

#4 Mark Horst

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Posted 30 December 2010 - 02:19 PM

Thanks for your replies. Ben, I'd be interested in the calculations that you mentioned to replace the Neph Sy and Lithium...
Thanks,
Mark

#5 Ben

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Posted 04 January 2011 - 11:47 AM

Thanks for your replies. Ben, I'd be interested in the calculations that you mentioned to replace the Neph Sy and Lithium...
Thanks,
Mark


I did a little googleing and it seems that the lithium and GB are the ingredients that are reacting. I thought that since lithium is such a small percentage it would be easy to replace. I've never worked with it myself unless it was sourced from more complex chemicals like spodumene. On a whim I looked around for a Frit that could supply the lithium. While some of the frit makers list them, I have not found a supplier that carries them. Look around the net or call some of the big online ceramic suppliers and see if you can find a high lithia frit.

Ben

#6 Ben

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Posted 04 January 2011 - 12:04 PM

Here are some frit numbers to look for
Fusion's F- 493
Pemco's P-609
General Color's GF-140

See if anyone has these available and if they have an analysis for them, then we can try and sub them into the recipe.

Ben

#7 Ben

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Posted 04 January 2011 - 10:29 PM

I did some more googleing and seems that the crystals may be soluble.
Let the glaze settle,
syphon off some of the water,
sieve out the crystals,
heat up the water you syphoned off and use it to dissolve the crystals,
return the water to the glaze and keep the glaze from getting too cold to prevent reforming crystals.

Give it a try and please, for the sake of those who may read this thread in the future, share your results with us.

Ben




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