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Hello,

 

I just unloaded a kiln load and noticed a substantial amount of pinging. My kiln is pretty much brand new (firing #3) and it reached cone 6. The pots are not crazed and hold water perfectly. The glaze seems to "fit" the clay and I see no glaze peeling. I have used both clay and glaze together before with no issues.

 

I cracked the kiln around 300 F and opened it at 250 F.

 

Hopefully, I can get an explanation.

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2 hours ago, Brandon Franks said:

The pots are not crazed and hold water perfectly

If the clay is vitrified (or very low absorption) then they will hold water without leaking, regardless of whether they are glazed or not.  Did you use cones to verify the kiln got to cone 6? If you hear pinging they are crazed, if the glazes are very dark it can be hard to see the craze lines. Sumi (calligraphy) ink brushed on the rinsed off under the tap will show craze lines on lighter coloured glazes. 

 

2 hours ago, Brandon Franks said:

I cracked the kiln around 300 F and opened it at 250 F.

Glaze shouldn't craze with doing this. 

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I had a Summer class at PSU where I made over 150 pieces, most fired in the collective kiln loads. I had a small apartment with my wife, and only storage inside was in the bedroom. The pinging at night was so noisy that we could not sleep! The pots went on to the back porch except for a few prize pieces.  By the next summer, almost every piece was gone. No more pinging.

In my own firings I have had some pinging and crazing, changes in glaze and bisque over the years had alleviated that. There is a science to firing, but then again there is an art in knowing when to turn up and when to turn it off. Cones do a lot to indicate when to turn it off, but not much else for when firing either with setter or manually. I often find that color/temperature is my best indicator of when to change switches.

 

best,

Pres

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Okay, a little update. I found that my white glaze (which I just made a new batch of) is crazing. The crazing lines are fairly close together. One thing that is different about the white glaze is the thickness. It is very thin, but that is the only thing that is different from normal. 

 

Are there any tips to prevent crazing. Maybe I should do a short hold at cone 6?

 

Your advice would be appreciated.

 

Thanks,

Brandon

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This is actually the first time I am using store bought glazes. I usually just make my own, but I love some of the combinations these glazes have when layered. All of them are from Continental Clay and Minnesota Clay. Sadly, I am unable to obtain the glaze recipes at this time, but I can give you my clay and its specifications.

 

I use a Standard 101 Buff Clay

C/02-9

Cone 02 Shrinkage 9.0% Absorption 4.5%

Cone 9 Shrinkage 12.0% Absorption 0.75%

 

Again, I fire to ^6 on the slow setting.

 

Thanks for all the replies, I have never had experience with commercial or crazing glaze, so this is very helpful,

Brandon

 

(I will provide a list and link to the glazes, if that helps anyone)

Twighlight Blue* https://www.continentalclay.com/detail.php?cat_id=425&sub_categoryID=&PID=1399
Matalic Green  
Gloss White* https://www.mnclay.com/AddToCart2.aspx?ProductGroup=HG7
BT12- Black  
NG12- Floting B  
Ng10- Espresso  
Buttercream* https://www.continentalclay.com/detail.php?cat_id=425&sub_categoryID=&PID=1399

 

*- all that I am able to tell have crazed

Edited by Brandon Franks
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With brushing commercial glazes, you're pretty much stuck. You can't get the recipe. You can either accept the crazing or try a different clay body. Crazing isn't necessarily a deal breaker, though, if the clay body is vitrified. Layering glazes complicates it even more. It's nearly impossible to get layered glazes to work perfectly, because two glazes that don't craze on their own may craze when layered.

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That makes it much more difficult to try and fix. If the craze lines are spaced far apart there is a slim chance you could correct the crazing with some added silica. Could you post a picture of the crazing?  If you do want to try the silica fix it's going to take some testing by weighing out glaze then adding a small percentage of silica, dipping a test tile and repeating with increasing amounts of silica.  Might be easier to try a different claybody you could try instead. 

Regarding that Standard 101 Buff clay, if the absorption has a posted figure of 0.75% at cone 9 then it might be high enough to be an issue for mugs, vases etc at cone 6. How to run an absorption test here. It's always a good idea to do your own absorption tests rather than relying on what the manufacturer posts.

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15 minutes ago, neilestrick said:

With brushing commercial glazes, you're pretty much stuck. You can't get the recipe. You can either accept the crazing or try a different clay body. Crazing isn't necessarily a deal breaker, though, if the clay body is vitrified. Layering glazes complicates it even more. It's nearly impossible to get layered glazes to work perfectly, because two glazes that don't craze on their own may craze when layered.

I actually dip but use multiple layers. However, I see most the crazing on the inside. I was actually looking to switch up my clay body, do you have any suggestions that work good with layering glaze.

 

Sorry if I am asking a lot, I have never felt with commercial glazes before and it is quite annoying. I am just going to stick to making my own in the future.

 

I am trying to post a picture but keep getting told the size is too big...

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19 minutes ago, Min said:

That makes it much more difficult to try and fix. If the craze lines are spaced far apart there is a slim chance you could correct the crazing with some added silica. Could you post a picture of the crazing?  If you do want to try the silica fix it's going to take some testing by weighing out glaze then adding a small percentage of silica, dipping a test tile and repeating with increasing amounts of silica.  Might be easier to try a different claybody you could try instead. 

Regarding that Standard 101 Buff clay, if the absorption has a posted figure of 0.75% at cone 9 then it might be high enough to be an issue for mugs, vases etc at cone 6. How to run an absorption test here. It's always a good idea to do your own absorption tests rather than relying on what the manufacturer posts.

I Keep trying to, but am having trouble uploading a file.

 

If you want, I could maybe email you a photo of the crazing.

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1 hour ago, neilestrick said:

As crazed as it is, by the time you add enough silica and kaolin to solve the crazing there's a good chance it will affect the melt. It may be easier to mix your own white glaze that you know works.

Do you think I could fix it with a different clay body? I am looking to switch my clay up, and this may just be the time to do it.

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Agree with Neil, as the crazing is so severe I wouldn't try the silica fix. It probably will fit a different claybody but it will be trial and error. If you are making functional pots I would ask your supplier for recommendations for a body that has less than 2% absorption and doesn't require low expansion glazes. Going forward, trying out new glaze / clay on test tiles before using on actual pots can save some aggravation. If you are firing to cone 6 then get a clay that matures at cone 6, not cone 9 like the Standard 101 Buff.

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16 minutes ago, Brandon Franks said:

Do you think I could fix it with a different clay body? I am looking to switch my clay up, and this may just be the time to do it.

It may work, but like Min said it'll be trial and error. If you have access to Standard clays, and you want a good stoneware body, I recommend #630, #112, and #211. If you want porcelain, then #365.

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19 minutes ago, neilestrick said:

It may work, but like Min said it'll be trial and error. If you have access to Standard clays, and you want a good stoneware body, I recommend #630, #112, and #211. If you want porcelain, then #365.

I was thinking of trying Standard 553 Buff clay-

 

C/4-6 Good clay body for production work. Contains fire clay and fine grog. Cone 6 Shrinkage 10.5% Absorption 1.25% 

 

Do you think this would be better?

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26 minutes ago, Brandon Franks said:

I was thinking of trying Standard 553 Buff clay-

 

C/4-6 Good clay body for production work. Contains fire clay and fine grog. Cone 6 Shrinkage 10.5% Absorption 1.25% 

 

Do you think this would be better?

That's a good clay if you like the feel and look of a buff. I prefer the #630 because it doesn't have grog. It's feels fairly smooth, but fireclay gives it enough tooth to be quite forgiving. I also prefer the color of the #630. Try them both!

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