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I Bisque Fired Too High, How Should I Glaze


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#1 rojelanogue

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Posted 12 July 2013 - 09:38 AM

So I'm silly and I bisqued my stoneware at cone 6 instead of cone 06. It was my first firing but I should know better. Anyway, the glaze is obviously not wanting to adhere/dry very well, and I'm wondering if it's a bad idea to glaze fire anyway (how is the glaze most likely to behave?), and if so what my best option is for at least making the pieces look prettier.



#2 mregecko

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Posted 12 July 2013 - 10:10 AM

You're not the first person to do this.

 

What is the actual vitrification temperature of your stoneware? ^6? ^10?

 

Regardless, it's going to be hard. The go-to "secret" that people use is heating the over-bisqued wares.

 

If you heat them in an oven (just below too-hot-to-handle), glaze will adhere a little easier.

 

Other than that, it's gonna be tough.



#3 Benzine

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Posted 12 July 2013 - 10:17 AM

Doesn't adding a little gum arabic, to the glaze, help too?


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#4 rojelanogue

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Posted 12 July 2013 - 10:30 AM

I figured I wasn't. Vitrification occurs at 6-10 but I'm not convinced cone 6 was actually achieved. It looked to me like I may have set the sitter to fall too early. I'm familiar with the clay body and the color suggests that it's pretty well matured but I'm just not sure. I thought something was wrong with the glaze itself until I realized what I'd actually done >:[]

 

Thanks for the tip. 



#5 OffCenter

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Posted 12 July 2013 - 10:41 AM

6-10 is too large of a maturity zone. If the manfacturer claims 6-10 it probably really matures at cone 10 and is not vitrified at cone 6. Does it stick to your tongue at all? I think you're in luck and all you have to do is take the advice above to get glaze on them and refire. But, firing to cone 6 is probably too low for that clay body and if you made a vase out of it and left it on a grand piano for a week it would leave a water mark.

 

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#6 rojelanogue

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Posted 12 July 2013 - 11:05 AM

I'm not home so I can't lick it right now put I will put it on my to do list lol. Anyway you are probably right Jim, I'll warm it up before glazing then glaze fire it hotter (with an appropriate glaze of course). Thanks all!



#7 Ben

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Posted 12 July 2013 - 11:08 AM

do an absorption test.

weigh a pot on a gram scale. soak it in water and weigh it again. see what percentage it changed.

In your case, the more the better.

As said, heat the pot.

Also, let the glaze settle and pour off some of the water. (Keep it to put it back in when you are done) The resulting glaze will be thicker and might help in getting a thick enough coating.

AND various gum additives will help the glaze stick too. You will have to experiement to get a result that works for you and since this is a limited event (hopefully you only have to try and fix this one time and not repetedly) I wouldn't put too much time into it.



#8 Pres

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Posted 12 July 2013 - 11:12 AM

6-10 is too large of a maturity zone. If the manfacturer claims 6-10 it probably really matures at cone 10 and is not vitrified at cone 6. Does it stick to your tongue at all? I think you're in luck and all you have to do is take the advice above to get glaze on them and refire. But, firing to cone 6 is probably too low for that clay body and if you made a vase out of it and left it on a grand piano for a week it would leave a water mark.

 

Jim

People need to realize that these wide range clays are not doing them much good at the lower firing ranges. I used a wide range clay first time I purchase, and noticed the lack of vitrificaliton on pieces then.  Next load was a ^5-6 clay, and has been ever since. I particularly like the ring you get form this the narrower range clays, and the fact that unglazed bottoms are much safer. Old mugs of the wide range clay started glaze cracking after about 5 years and glaze flaked off in places with clay after about 7. Glazes were good, as I used the same formulas I use some of the same these days.


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#9 rojelanogue

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Posted 12 July 2013 - 11:31 AM

Pres,

 

This raises an issue I've always been confused about. How do you tell if it's vitrified satisfactorily?



#10 neilestrick

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Posted 12 July 2013 - 12:07 PM

Don't waste your time trying to glaze those pots. It will take 10 times longer than normal, won't go on evenly, and probably won't be thick enough to look good. Chalk it up to experience, and get started on a new batch.


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#11 Pres

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Posted 12 July 2013 - 12:10 PM

That is a tough one, but over the years I have found that my ears(even with hearing aids) tell me a lot about a pot. I listen to the ring when knocked with a light wooden handle or mallet. High pitched ring with lasting timbre would be a lead to a decently vitirfied piece. Other end of this is that I listen to bisque fired pieces in the same way-you can always hear a double sound in a hairline cracked piece, even if you can't see a crack. I also check glazed fired pieces the same way to check for cracks I don't see. Once you discover it by sound you can find it by close looking with magnifing glass-but it is too late anyway.

If the clay is not vitrified, then the ring will be lower in pitch and have less duration. Heck, I even talk to my closed jar type pots when throwing them, if I hear a certain kind of echo, then the piece is of good thinness, and even.


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#12 Mark C.

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Posted 12 July 2013 - 02:56 PM

Don't waste your time trying to glaze those pots. It will take 10 times longer than normal, won't go on evenly, and probably won't be thick enough to look good. Chalk it up to experience, and get started on a new batch.

This is the best advice-as these will be a bear to deal with. I would spend my time rethrowing more pots. The take away is pay more atention when dialing in the computer program on the kiln.

If you insist on trying to stick glaze to them warm them 1st then glaze.

If this is a cone 10 clay I would toss them for sure as thats just the wrong clay for cone 6.

Mark


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#13 rojelanogue

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Posted 12 July 2013 - 06:46 PM

I'm only considering trying to save two--they are sculptural pieces I'm fond of that took a bit of time to make. They look kind of okay as is though, so I might just leave them if glazing is not likely to work. I am now confused about what cone my clay is best fired to. It's not a computerized kiln though, I put the wrong cone in the sitter



#14 Min

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Posted 12 July 2013 - 07:17 PM

For the sculptual pieces you could also use non fired products on them, rubNbuff, acrylic paints, shoe polish etc, or just leave them as is like you said. 

 

As far as knowing what cone to flre your clay to, if it's sold as a ^6 thru ^10 clay it will be underfired in the lower ranges and will probably weep. If you get bloats with a clay it is usually from overfiring. 

 

Porosity and absorption are 2 seperate things, if your porosity is below 2% your pots shouldn't leak. Below is link for testing outdoor ceramics for both, the testing is applicable for dishware also. After doing those tests (and your porosity is below 2%) then I would fill an unglazed pot with water and leave it on newsprint for a week. If the newsprint has wrinkles then your pot is weeping. (or you could ask Jim to test it on his grand piano ; )

 

http://digitalfire.c...ramics_105.html

 

Min






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