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I decided to check my pots from my first glaze firing by placing some water in them and let the popt sit on top of some paper. I'm not a happy camper.

 

I fired 2 different clays, Standard 112 and Amaco 46 and both weep. Amaco took about 30 hours while Standard took about 5 hours.

 

From my inexperienced eye and based on a witness cone I was around ^5-1/2.

 

I'm not really sure what to check or to do to make sure my next batch vitrifies.

 

Suggestions would be appreciated.

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From Standard's web site: 112 BROWN CLAY - Cone 4-6

 

Plastic clay for wheel and modeling. The addition of granular manganese gives a speckled surface. The ideal temperature for developing best color tone is cone 5. Good results may be expected in reduction or oxidation firing. Suggested bisque temperature C/04. Shrinkage: 12% at C/4, 12.5% at C/6. Absorption: 4.5% at C/4, 2.5% at C/6.

 

At cone 5 1/2, your absorption rate is probably in the 3% to 3 1/2% range. To vitrify, you would need to go above cone 6 (or do a hold at cone 6), according to their absorption information. Going that high, you will see some difference in color of the clay body.

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How attached are you to the Amaco? It’s listed as a cone 5-10 clay @ Cone 5, 1.8%; Cone 10, 0% absorption. I would question the 1.8 figure if it can go to 10 without being overfired. I’m surprised the Amaco took longer than the Standard to weep, did the Amaco have a thicker base? Were they in the same part of the kiln?

 

 

To keep the kiln on after the sitter weight (arm) has dropped raise it back up and press the plunger (button) then gently lower the weight. Kiln stays on until you shut if off. I would go by witness cones over the sitter cone for accuracy. Sitter bars seem to have less user error than sitter cones.

 

Did you see this bit from Amaco? (semi vitreous @ ^5)

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What cone did you put in your sitter? If it was a 6, but the kiln only fired to 5 1/2, you need to adjust the sitter.

 

I had a ^5 in the sitter.

When I had ordered witness cones I received two boxes of ^6 and one ^4 instead of ^4 ^5 ^6 I ordered - so I'm really guessing based on how the ^6 looked. Add to that my inexperience.

 

 

How attached are you to the Amaco? It’s listed as a cone 5-10 clay @ Cone 5, 1.8%; Cone 10, 0% absorption. I would question the 1.8 figure if it can go to 10 without being overfired. I’m surprised the Amaco took longer than the Standard to weep, did the Amaco have a thicker base? Were they in the same part of the kiln?

 

 

To keep the kiln on after the sitter weight (arm) has dropped raise it back up and press the plunger (button) then gently lower the weight. Kiln stays on until you shut if off. I would go by witness cones over the sitter cone for accuracy. Sitter bars seem to have less user error than sitter cones.

 

Did you see this bit from Amaco? (semi vitreous @ ^5)

 

Not at all attached to the Amaco, at the time I ordered it from amazon it was all I could get.

 

This from the link you provided

"The bisque is very dense and semi-vitreous"

I had assumed they were referring to the ^04 bisque firing. not the ^5 glase firing.

 

Yes, the Amaco had a thicker base and I don't remember if they were in the same part of the kiln.

 

Good to know about how to get a hold with a sitter and its easy to see why cones, with their taper can cause more of an error than a bar. Thanks

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yeah, it's not written very well. Bisque isn't going to be semi vitreous though.

 

I prefer stoneware with under 2% absorption if you are making pots that will hold liquids. Gives you a bit of wiggle room if part of your kiln fires a bit cooler.  Still have to test though as manufacturers have that +/- 1% in the range.

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Thanks Min

 

Mark, I've come to the same conclusion.

 

It seems I wrongly assumed that the glaze would help seal the pot for liquids. To be honest I hadn't realize that absorption rate referred to weeping. 

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To keep the kiln on after the sitter weight (arm) has dropped raise it back up and press the plunger (button) then gently lower the weight. Kiln stays on until you shut if off. 

 

 

 

And don't walk away and leave it.  Set a timer and stay close.

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Thanks for all the advice everyone.

 

I threw about 40 mugs with the Standard 112 clay, of which 34 were recycled and the rest are now bone dry. (Took me that long until I liked the handles I was making.)  Going forward, once these mugs are glazed and fired would I be able to use them for coffee and wash them in a dishwasher?

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If I was using the Standard 112 clay I would fire the mugs to a hot cone 6. I would put a ^6 cone in the sitter but also a cone pack with ^5, ^6 and ^7 cones in front of each spy hole. Monitor the firing closely towards the end. When you see 5 down start checking the witness cones every 20 minutes or so. Should take about an hour for ^6 to go down after 5 is down, but every kiln is different so don’t just time it but check the cones. Once 6 is down and the sitter has tripped then I would re-set the sitter, do it fast as the temp will drop really fast, to stay on and check the cones every 10-15 minutes. I would fire until ^7 is at about 2:00 o'clock position. (assuming cones are falling to the right)

 

Also, instead of just going by whether the pots weep or not I would suggest doing an actual absorption test with a sample on each shelf. Put the sample in the middle of each shelf so it’s a worst case scenario (thermal lag with samples in middle of kiln)

 

Standard lists that clay as 2.5% @ ^6 with the +/- 1% fudge factor. Laguna BMix ^5 is listed at 2.3% and they sell it by the trainloads without weeping complaints so in theory you should be okay but TEST it! Getting into the area of porosity versus absorption and whether they are the same thing in clay or not. Would be good if someone here who uses this clay would share their findings.

 

 

If you scroll down about 2/3 the way on this page there are instructions for doing an absorption test. It only takes a few minutes of actual work time and can save the frustrations and pain in the bum issues you are running into now if you do this prior to making a ton of work.

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The key to Mins advice is you need to be there when the sitter drops and push the on Button when it drops .I think a digital pyrometer if you do not have one installed will really help you as well.Easy to connect to your thermocouple if one is in kiln already if not easy to install. She has given you a detailed firing option which may cure your mugs. I would do that absorption test to know where this clay stands.

​Who said ceramics would be easy and fun?

 

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I have no problem being with the kiln, there is always something to do around the studio. Since its a small kiln it took 5 1/4 hrs for the sitter to drop on the last glaze firing so its no big deal. I'll figure an hour more for ^6+

 

 

 

 

​Who said ceramics would be easy and fun?

Exactly!!! why else would you want to do anything else. 

 

 

I've always enjoyed a challenge that's what makes it fun. 

 

As nerd, put it Obsessive Clay Disorder OCD

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Its possible that my misunderstanding of the term weeping may have lead to some confusion.

 

I had place water in the pots I mentioned in my first post on sheets of paper and after the times I reported I found the paper had wrinkled.

 

Is this considered weeping?

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