Laminating? Did I make puff pastry?

[Juliagoolia]

So I had a massive number of bowls blow up last week in my bisque fire. I figure it was the thick bottoms. I had gone through one while trimming and then panicked and left the rest too thick. So boom! I had stacked bowls within bowls so I have no idea how many blew up because their friend and they just went along for fun. 

I noticed one surviving mug had a weird split along the top of the rim, like, well, puff pastry that was separating. I glazed it anyway to test a new glaze, and then when I unloaded my glaze fire I found another bowl that had the same thing. I don't think it had it after the bisque but I don't know, my iron is low, I'm homeschooling  and I'm working full time from my living room, so there is a LOT of room for error.

I took a picture. It is a mid fire buff stone ware (plainsman 370). It could have been reclaim, but I don't recall. I had painted it with underglaze and then applied a clear. I did introduce some moisture but I didn't fire it until the day after glazing (and about 5 days after underglaze). As noted, one mug did this after bisque from the same load.

Any ideas?

Tia!

[Juliagoolia]

Hold up, I didn't glaze the bisque one. I just found it! So that means 2 did this weird peeling thing in the glaze fire. 

[Min]

6 hours ago, Juliagoolia said:

So I had a massive number of bowls blow up last week in my bisque fire. I figure it was the thick bottoms. I had gone through one while trimming and then panicked and left the rest too thick. So boom! I had stacked bowls within bowls so I have no idea how many blew up because their friend and they just went along for fun. 

Thick is okay as long as the clay is given time to be bone dry once you start heating up past 200 - 250F. Candling the kiln if you aren't sure is a good idea. If you aren't sure if the pots are dry going into the kiln put one up to your cheek and another that you know for sure is dry on your other cheek. If the one you aren't sure about feels cooler then it's still damp and either needs to be left for longer to dry or to be candled. (pots should be from the same room so they are the same temperature)

Would you give some info on how you made the pots with the horizontal splits in the rims? 

 

[Juliagoolia]

2 hours ago, Min said:

Thick is okay as long as the clay is given time to be bone dry once you start heating up past 200 - 250F. Candling the kiln if you aren't sure is a good idea. If you aren't sure if the pots are dry going into the kiln put one up to your cheek and another that you know for sure is dry on your other cheek. If the one you aren't sure about feels cooler then it's still damp and either needs to be left for longer to dry or to be candled. (pots should be from the same room so they are the same temperature)

Would you give some info on how you made the pots with the horizontal splits in the rims? 

 

Hi Min

They were all wheel thrown. I've never had this type of split show up, but I've also never blown up anything in the kiln, let alone multiple bowls in one firing. The one that split after the bisque was a small wine cup, the two that I saw after the glaze fire were a small mixing bowl and another wine cup. 

 

Thanks!

[Min]

I've never seen splits running parallel to the rim like you are getting, or read about them.. The rim in the second picture looks like it has some vertical sheering which makes me wonder if could be from weight bearing. If you have ruled out any process during  forming rims and didn't stack a lot of weight on them when drying or firing that could have caused it then I'ld  contact Plainsman with the clay batch number and close ups of the splits and see what they have to say.

[Babs]

Are you compressing the rim after each pull up?

How wet are you throwing?

Think maybe footrings of pots a bit moist...

Just wondering if maybe you are encorporating any slip from throwing into the rim of the pot?

[Juliagoolia]

Hi Babs

I throw pretty somewhat on the wet side, but not too much. I usually compress the rim on every pull. And I didn't use any slip on this. 

Min - when you think weight bearing are you thinking in the kiln or during drying? 

[Min]

2 hours ago, Juliagoolia said:

Min - when you think weight bearing are you thinking in the kiln or during drying? 

2nd picture looks like there are a couple fractures which made me wonder if it was either thunked on the rim or had too much weight on it at some point. They are unusual cracks.