clayenthusiast
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Posts posted by clayenthusiast
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On 5/21/2023 at 10:06 AM, Min said:
One more thought, do you have a new supply of talc? Is "recent" since a new batch? Any material changes? Glaze still would probably have fit issues for some claybodies, I would be surprised if one glaze fit a wide range of bodies well.
For sure the glaze expansion is too low on the bodies when you get dunting on large flat surfaces. Pots with glaze just on one side and a low expansion glaze fighting against one with a notably higher expansion on the other side of the pot (as with liner vs exterior glaze) will also dunt. Given that calculated COE figures are not accurate with matte (or semi matte) glazes you need to look at what is in the recipe and the properties of those materials.
We have received a new supply of talc and have mixed a batch with the new material. Are there changes in the mining of talc as of late or its properties? I do believe I heard something of the like. One of my mentors also inquired about the talc. But even prior it never behaved well as a glaze but as of late has seemingly worsened.
Thank you for the info on dunting. This helps better my understanding and makes sense.
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On 5/19/2023 at 8:00 AM, Min said:
Yup, there are definitely lots of white glaze recipes available but I think we need to know if @clayenthusiast is looking for another dolomite (or talc) high magnesium satin glaze or is okay with a gloss.
I'm really hoping to keep the glaze recipe as close as possible.
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On 5/20/2023 at 9:32 PM, neilestrick said:
I agree. The kaolin, silica, and bentonite make up almost 50% of this glaze. There's just not enough fluxing going on there. I'm wondering if there was a problem with converting the recipe at some point since the numbers add up in a strange way. Maybe someone messed up the math?
Good to know about the overly dominate clay in this recipe. Also, I've honestly always wondered the same thing about the way the numbers add up. I may do some digging into some of the historical notes for this studio or other versions of this same recipe perhaps. I might be playing around with the percentage of clay and run some tests.
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On 5/20/2023 at 8:57 PM, BobMagnuson said:
Sorry I'm late to this conversation. I see 3 problems with this glaze. First, the clay content is too high, which can cause shrinkage and separation before firing. It might not be noticeable before firing , but can show up as shivering out of the kiln. Second, the coefficient of expansion is quite low, which could be an issue with some clay bodies. And finally, it looks like it might be applied too thick. The first 2 issues could be resolved by reducing the kaolin by 25% or so. (Run a few tests in that neighborhood.) Finally, if you're dipping your glaze, keep the specific gravity below 1.5. 1.45 works for me with a 5 second dip.
If the problem is the clay content, another solution would be to replace some (half?) of the kaolin with calcined kaolin. That way you can keep the chemistry the same while reducing the pre-fire shrinkage.
I am also late to the reply on my own thread, thanks for the patience. I was away from my desk for a few days. This right here is the knowledge I was hoping to garner. This it the kind of test I would like to run to see if I can help these issues. I will definitely be running this test. Thank you thank you for sharing your knowledge!
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On 5/18/2023 at 7:42 PM, Mark C. said:
Either change the body or the glaze
lots of white glazes out there
Might be changing the clay body, mainly because we have a incredible library of tiles for all of our glaze combinations.
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23 hours ago, Magnolia Mud Research said:
Do you have a clear glaze that works OK all the time?
if so, just add some Zircopax to your clear glaze and you will have a white glaze.
the amount of Zircopax will probably be somewhere between 4 and 8 %.LT
I love knowing this. Thank you!
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On 5/18/2023 at 5:27 PM, Min said:
Are you looking to keep the magnesium satin look to the glaze?
Yes I am interested in keeping the characteristics of the glaze and the recipe as close as possible. We have an extensive library of glaze combination tiles that I would like to have them still apply if at all as all possible.
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Hi Clay Community,
I am needing some input on possible actions to take to prevent the severity of shivering that has been taking place in our studio. We fire cone 10 gas reduction. We have 4 different clay bodies and our reclaim clay. The white glaze is having some compatibility and fit issues with our stoneware clays. And of course the worst being with our red heavy iron baring stoneware. This combination of stoneware and our white glaze is the only culprit. The white glaze is not shivering on the porcelainuos clays. This combo also has a tendency to not behave if used primarily as a liner glaze especially on just the top of large surface areas like plates and will crack the piece all the way through post firing or during cooling.
Glaze Recipe -
Coleman White
Custer Fledspar 38.63
Whiting 14.65
Talc 14.65
Kaolin 34.64
Silica 27.97
Bentonite 2.67
Zircopax 8
Any advice on ways to adjust the glaze to create a better fit or compatibility would be great. Or possible adjustments to the firing to prevent the severity of our recent shivering incidents.
Thank you for any input!
Warmly,
Clay Enthusiast
HELP! Severe Shivering White Glaze
in Clay and Glaze Chemistry
Posted
I appreciate it, thank you! Also how amazing that it's a Betty Woodman recipe.