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Glazing bubbles...help ? :/

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#1 1Artsygirl



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Posted 03 April 2013 - 12:40 PM

Hello to everyone ! My name is Penny. I've been throwing for a number of years and changed to stoneware about a year ago. I decided to invest big time and bought a ton of ingredients to make my own glazes. I've made progress and have some good results starting to happen. Actually.. That was until about 3 weeks ago. It started with a pot with a few bubble craters. Over the next few firings, it's getting worse. It's with all of the glazes in this last kiln load. They all have bubbles and now on top of that, I'm getting a strange texture across most of the pots. It's almost like someone blew something over the pots. If the pot was covered, the inside was fine.
I fire to cone 5 with orton cones. (Not rich enough for a fancy dancy kiln. ) I'm using Sybil clay with speckles. All of my glazes have worked on previous firings. ...but this is my first kiln load of everything being altered with additional glazes. Basically... Why am I getting more and more bubbles and craters? Why did the entire kiln load get this weird surface texture?
I'm enclosing photos of 3 samples. Thank you! Thank you! Thank you !,,,!

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#2 TJR


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Posted 03 April 2013 - 01:02 PM

Could be a BUNCH of issues.I suggest keeping a kiln log so that you can keep track of your firings. I fire in a used $750.00 kiln with a sitter. Not everyone has fancy computers.
1.You may be firing too quickly and not giving the glaze a chance to develop
2.Your glaze may be too thick. Try adding a bit of water-not too much. Should be the consistency of cream.
3.You could have dust on your pots. I rinse all my pots in a bucket of water, then let them dry over night before I glaze them.
4.You could have dust in the kiln. Vacuum it out with a shop vac, especially the lid.
5.It could be your clay body is off gassing. Maybe you need to bisque at a higher temp. I bisque at cone 06.
You see what I mean about the litany of problems?

#3 Marcia Selsor

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Posted 03 April 2013 - 01:10 PM

I only saw the green casserole and no other pictures.
The buubles are not pin holing. It looks more like the glaze got sucked into the body. Did you see bubbles on the surface before firing? Sometimes you need to smooth the out by rubbing with a dry finger.
I agree, bisque to ^06 or maybe higher to 04.

Marcia Selsor, Professor Emerita,Montana State University-Billings

#4 OffCenter


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Posted 03 April 2013 - 02:05 PM

The one pot you posted a picture of looks under fired to me. Refire it to cone 6.

E pur si muove.

"But it does move," said Galileo under his breath.

#5 neilestrick


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Posted 03 April 2013 - 02:12 PM

I have seen that problem in a lot of cone 5/6 glazes. It's often a case of the glaze being unstable, too much flux. Try adding equal parts EPK and flint (silica) in 2% increments. At equal parts it won't affect the silica/alumina ration of the glaze (glossiness), but will stabilize it. It may take up to 10% or more. If this started happening with a glaze bucket that was previously working fine, I'd say it's settling out, and you'r not getting it mixed well enough before use. Add 1/2% by dry weight epsom salts to every bucket you make to help keep it suspended.

Neil Estrick
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Owner, Neil Estrick Gallery, LLC

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#6 1Artsygirl



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Posted 04 April 2013 - 01:52 AM

Penny here again..
I was unable to put more than one photo on the page because of my ipad mini....so here is photo Nbr 2. and 3. the cup shows the overall texture of most of the kiln load.which by the way, are different glazes. The third photo is a close up of the top of the cassarole dish.May I ask, with epson salt, do I dissolve it in water before I add it to the recipe? Why is it important to smooth over bubbles made when dipping pots?
Now that I have read your suggestions, I will agree that some of my glazes r a bit thicker than cream.maybe this is the reason for the bubbles?
I had a pot blow in my last kiln load and I didn't completely clean out the shards so maybe they are affecting the glazes?
Thanks a bunch to everyone with their answers!

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#7 Ben


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Posted 04 April 2013 - 08:13 AM

It would help to know all the data.
What clay body?
What is your bisquing schedule?
What are the glaze formulas that you used?
Have those glazes worked in the past?
Have you mixed a new batch of any of the glazes since the last successful firing?


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