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Pulled this out this morning. Had no idea it had a crack. I can feel the crack on the inside. This was going to a customer. I like to try out items before letting them go out to the world. Good thing I did... This glaze combo has been used numerous times before with no issues. It is White Satin Matte inside and a Turquoise Satin Matte outside that Marcia posted awhile back. Must be the area was thinner, but it didn't feel like it when throwing it.

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Min;

it is White Satin Matte. I've had it for a long time - found it on the web. But when I got Britt's ^6 glaze book there it was on page 130. I have altered the glaze a little by changing GB for Borax and adding 3% more zircopax and 3% titanium dioxide. It has always worked well for me except I wanted it to cover a little better without being thickly applied that is why I added the zirco and titanium.

 

White Satin Matt

  Talc........................    14.00  
  Kona F-4 Feldspar...........    19.80  
  EP Kaolin...................     5.00  
  Boraq.......................    31.60  
  Silica......................    29.60  
  Zircopax....................     8.10
  Titanium Dioxide............     3.00
  Bentonite...................     2.00  
                              =========
                                 113.10

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John, could you point me in the direction of Marcia's outside glaze? I'm wondering if it's a combination of a high expansion on one side and low on the other combined with a thin area? Just a wild hunch. Still don't get the dribbles only in limited spots though. Have you ever frozen a pot with this combo of glazes then poured boiling water into it? 

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Min,

 

Have not done the freeze/ boil test - will do.

 

WSM  -            Thermal Expansion:    6.21

 

The TSM glaze is nearly identical to Heino Blue on page 120 of Britt ^6 book. I took the liberty of replacing Barium with .75 of Strontium.

 

Turquoise Satin Matte

  Nepheline Syenite A270......    61.50             Thermal Expansion:    8.80
  Strontium Carbonate.........    20.90  
  Silica......................     7.70  
  OM #4 Ball Clay.............     6.60  
  Lithium Carbonate...........     3.30  
  Copper Carbonate............     3.50  
  Bentonite...................     4.00  
 *Epsom Salts.................     1.00  
                              =========
                                 108.50

 

Heino Blue

  Nepheline Syenite A270......    61.60             Thermal Expansion:    8.91
  Silica......................     7.60  
  OM #4 Ball Clay.............     6.60  
  Strontium Carbonate.........    21.30  
  Lithium Carbonate...........     2.90  
  Copper Carbonate............     3.00  
  Bentonite...................     2.00  
                              =========
                                 105.00
 

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I am not a midrange fire person but satin matts I think are poor inside glaze choices on cleanablity.(new word)

I know for sure they foam beer (I'm not a drinker myself but learned this in the 70's)

My guess is the simi matt on the inside and  matt outside is your issue

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COE figures don't work with matte glazes. Just looking at the ingredients here, not using software, there is a fair bit of nepsy in the outside glaze (high expansion). Maybe do a thick layer of liner glaze inside the thinnest cylinder shape you have with no glaze on the outside, and another one with both a thick white liner plus the green outside. Try them both with the freezer/boiling water test. 

 

Could just be a thin spot in the clay wall with a thick glaze layer.

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There was another mug matching this one in the kiln load. Did the freeze/boil water test. Froze the mug overnight. Heard no pinging or cracking and water is still in the mug.

 

Below are shards from the leaky mug. The body is much thicker than the ribbed area. I left extra clay in the ribbed area, not enough, or take more clay out of the body.

 

 

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The thickness of the clay and glaze in the shards photo looks about 1/8" at the break, is that about right? Clay is a bit thick at the bottom of the pot but that shouldn't come into it.

 

Re freezing / pouring boiling water inside, I was wondering if there was a fit issue between the 2 glazes. Fair bit of talc in the liner glaze, plus even though zircopax raises the coe numbers it doesn't really do that. The silica in the zircopax helps bring coe down, the zircon raises it but it doesn't enter the melt so it doesn't come into play with expansion and actually will decrease crazing. Green glaze looks like a much higher expansion one. So just going on what ingredients are in the 2 glazes I considered the fit of the 2 on the same pot, sounds like you ruled that out with the freezer test. It wouldn't be crazing but rather dunting I was thinking of. (mug you tested same thin area?)

 

I'm still stumped. 

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Min,

 

Yep 1/8 inch. The tester mug was same thinness, basically the same mug. I have this glaze combo on other, not so stressed mug forms and have been drinking coffee from them for 6 months. In fact, I poured the water out of freeze/boil tester mug, after it had sat for 2 hours, and drank a coffee from it this morning. The handle felt cool to the touch after sitting just 15 minutes with the hot water.

 

Thank You for your thoughts.

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  • 3 weeks later...

This post had to be pulled back up.

 

The thought was the the ribbed cuts were to thin that is why the leaking. Wrong! Below is more of the same type of mug but it crazed in the smooth body section, and water oozes out of the craze lines. It also leaks out of the ribbed cuts also.

 

But, on a previously made mug with a smooth body top to bottom it doesn't craze and doesn't leak, see the mug on far right. Why no crazing and leaking on the smooth body? Same liner ame turquoise

 

What must be learned from this?

 

Can the White Satin Matte liner be altered? Is it best to find another white liner?

Can the present Turquoise Satin Matte be changed to stop crazing? Or, Is it best to find a new turquoise?

 

 

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I have a few theories. If this clay is <1% at cone 6 the glaze shouldn't even really matter. I have several pots without any glaze on the inside and they don't seep out the bottom. My throwing pot has no glaze in it and it holds water for a long time and hasn't seeped yet. I have several flower vases in my house with no glaze in them as well. 

 

I think that the glaze is causing microcracks in your body which is causing the leaks. Cause if you look at picture 2 and zoom in near the middle of that mug it looks like a tree's root system of cracks.

 

The other idea is that your clay isn't vitrified and your other glazes are keeping the water from seeping but this one is crazing and allowing water to pass through. 

 

Just some ideas. Have you tried firing this clay with no glaze and seeing if it seeps?

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Joseph, Thanks for your thoughts. I have not fired this clay without a glaze on the pot. Will do this very next firing. There is something about the stresses put on the mug with the ribbed cuts. I answered Min, earlier, about a freeze/ boil water test. This glaze combo passed the test with that smooth bodied mug, the far right pic.

 

This clay, Laguna #55 WC 6-7, is the only clay I have used for the past 8 years. Have numerous mugs and soup mugs out in the world with this white liner but different exterior glazes. This is the first times the turquoise has been used.

 

Needless to say testing is going on with a different white liners and trying to find a like colored turquoise. The sad part is I have to get 2 of these mugs, white liner with turquoise outside, to a customer before Christmas.

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I'm seriously wondering if you have a bad batch of clay. I would do a glaze free flat bottom cylinder from this lot number of clay and if you have any of your older stock left or some from another lot number I would make some test pots with that also. No glaze, fire the same way as you do your glaze firing then fill them with water and set them on newsprint for a week. With weeping as bad as in your last pics I would guess the paper will be damp within about 12 hours. I would also contact the manufacturer plus your supplier and ask if they have had any similar issues reported. If you are confident it was fired to ^6 then I would say it could be short on flux.

 

Re turquoise glaze, do you have Britt's Mid Range Glazes book? If you do have a look at the glaze combo on page 110 and again on page129. Autumn's Crystal Matte over Glossy Base 1 with 3% copper carb. It somewhat resembles the look of your turquoise. (maybe run some tests with that at the same time as the naked cylinders tests) If you are okay with a gloss liner then you could use the same Glossy Base 1 and add zircopax to make white.

 

If you don't have that book let me know and I'll email you recipes and pics if you are interested.

 

Edit: Do you have a pot with this batch of clay that you haven't used or tested? Could save some time with testing by thoroughly drying the pot out in your oven, weigh it really accurately, put it in a saucepan covered in water and simmer it all day, then let it cool in the water, towel dry it and reweigh then do the math for absorption figure. Obviously not as accurate as using an unglazed piece but should supply some info.

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Min,

 

Yes have the book and have tested Autumn's Crystal Matte. Also use Bright Sky Blue which uses the Glossy Base 1 recipe. Was reading Hopper's Spectrum book and he says an alkaline glaze with copper carb may produce a turquoise. Will do the simmer method today. Let you know the results later.

 

I keep coming back to the turquoise/ white satin matte mugs that do NOT weep. WHY? Going to break one of these mugs and compare the wall thickness to the these that do weep. Maybe that is where the problem is. The color of the turquoise is perfect to me - what I think of for turquoise. I am a bit stubborn.

 

Thank You.

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Hmmmm, years ago, I was throwing large jars, @25", during the bisque, every one of them got spiral cracks from top to bottom, almost as if they were made of a wrapped ribbon like a spring. I thought of all of the issues possible, tried changing the way I threw them, and other things. . .same spiral cracks. So the last thing I tried was to readjust the bisque fire for a longer climb to 1100F. and then a longer climb to ^6, with a cool down to 900F. that entailed firing down. This happened with one clay body, and the bisque made all the difference in the survival of the forms. Glaze firing was as usual, with no problems.

 

best,

Pres

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