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AtomicAxe

glaze 'flaking' off

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Alrighty then! I encountered a problem with a glaze that I have never came across before. The glaze is popping off the piece. To be specific, it's only when I'm layering and it's the top layer ... but up to 2 inches below that flakes off as well ... sometimes onto my kiln shelf or other peices, though most seems to contain itself on the pot or in the pot which then gets thick and bubbles making a lumpy and fragile layer. exposed clay still fluxes so something remains of the glaze that does pop off and leads me to believe it's before it even starts to glow. Standard cone 6 firing with kiln sitter. doesn't matter if I slow fire, or fast fire.

 

Could the glaze be lacking in clay? and i'm just spitballing here ... glaze contains borax and I needed some epson salts to suspend it in the glaze ... would this do it? Or would something else be at work with this?

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Alrighty then! I encountered a problem with a glaze that I have never came across before. The glaze is popping off the piece. To be specific, it's only when I'm layering and it's the top layer ... but up to 2 inches below that flakes off as well ... sometimes onto my kiln shelf or other peices, though most seems to contain itself on the pot or in the pot which then gets thick and bubbles making a lumpy and fragile layer. exposed clay still fluxes so something remains of the glaze that does pop off and leads me to believe it's before it even starts to glow. Standard cone 6 firing with kiln sitter. doesn't matter if I slow fire, or fast fire.

 

Could the glaze be lacking in clay? and i'm just spitballing here ... glaze contains borax and I needed some epson salts to suspend it in the glaze ... would this do it? Or would something else be at work with this?

 

 

You said this is happening when you are layering. I had this same sort of thing happen to me a few years ago. I determined in the end, that my glazes were a little too thick for the layering I was doing, and that I might be letting the layers dry too much before applying the next coat. Thinning the glaze slightly and re-dipping just after the glaze became dull solved the problem for me. As to the Epsom salts, I always add 2 tbsp of saturated liquid to my glazes that settle quick. Never had a problem. I know that you are very cognizant of glazes and glaze chemistry, more so than I, but maybe this is part or all of your problem.

 

best,

Preston

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Thanks for the reply Pres. Thickness could definitely be the issue ... this 'glaze' for lack of a better word came from 62 low fire slip tests that were not up to par of brushable fluxing greenware slip that lacks things like gum arabic and other organic binders (hard to accomplish, but do-able) ... think one day art camp stuff, students can make a piece of work, paint it, pick it up 2 days later ... found that the drops made a rather interesting glaze at cone 6, slightly runny, milky in weird ways (probably due to the small amount of borax messing up the melt) and layered to do some different things on top of iron based glazes. I thinned it out a good deal, but my first inclination was that it was contracting way too much off the pieces which would come from materials like talc but this 'glaze' has none of that in it. Maybe a lack of clay or specifically perhaps a calcined epk to help it bind more.

 

My next round of tests are going to be happening soon, so I will try thinning the mix more ... I have almost a 5 gallon bucket of the stuff so the frugal studio potter in me is screaming 'MAKE IT WORK'

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I would agree that the glaze is too thick. There is also if you glaze the inside you have water in the bisk, then glaze the outside, more water in the bisk, then another layer, still more water in the bisk.If this happens, there can be too much water for the glaze to adhere and it separateseasily from the pot.

You might try letting the interior glaze dry more before doing the outside. The other thing is that the clay part of the glaze, first coat and second coat bod together so well that as it drys it pulls the glaze from the pot.

If the glaze recipe calls for a high % of clay, 10 % and over use 50% calcined clay and 50%raw clay to keep the clay shrinkage to a minimum.

This has worked well for my glazes

Hope this helps

Wyndham

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GEE, AXE, i thought i was the only one who has had this problem. mine was not on a thick application, i thought it was somehow too vertical and it just folded down. hope there are more answers.

 

BTW, thanks for changing the avatar.

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Oh, you guys are lucky right now with my current avatar. When it hits Halloween season you'll love that one (probably not).

 

As for the glaze, tried it with a more complete drying on base later then top layer ... came in the studio this morning to find that top glaze completely on the shelf. So issue is starting to become less drying and more shrinkage of the ingredients ... it was fine on my tests with it as the only glaze and on the bottom. But oh well, I will find a use for this quite lovely mistake glaze that angers me to the point of RAGE!

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Since you have tried variables of thickness and drying and that didn't solve it how about bisque firing on the base glaze then applying the 2nd glaze? Min

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If you want to post the glaze, I have a cone 6 coming up soon, I'll give it a try.

If you have a lot of frit and little clay, well anyway I'll give it a try if you want.

Wyndham

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No need to post the glaze .. it's all drops from tests. 

 

I did on the other hand find a use for it ... on my refires ... seems to stick well without flaking on vitreous ware.

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I have a glaze combo that does the same thing. I always thought it looked more like and extreme crawl than flaking. In mine, the base glaze is a slip glaze, really high in Redart. I tried all sorts of things to fix it, but never really got it 100%. The one thing that helped the most was letting the first layer dry a lot before dipping the second layer.

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Yeah, I think it's just the clay content in the top glaze.  sticks like a champ to refires, and as the first glaze ...

 

Tried drying all the way then coating the second time ... here are the results :-P  just not a glaze i'm going to double dip I suppose.

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