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mregecko

Clay bloating - IMCO Stoneware 1c

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mregecko    18

Hello everyone -- just wanted to post here some experiences I've had and see if anyone has some recommendations and/or similar troubles.

 

I've been working with IMCO Stoneware 1-C for a few months now, loving it as a mid-firing stoneware (texture and color).

 

However, when I fire it to the advertised maturation temperature of ^6, I see a good bit of bloating.

 

At ^5 everything seems fine.

 

To cover the normal basic troubleshooting, I've noticed bloating between ^5 and ^6 considering:

 

  • Same clay batch and even BAG
  • Same bisque firing
  • No carbon coring noticeable when broken open
  • Pyrometric cones and digital readouts confirming temperature
  • Same glaze treatments
  • Pieces were identical [or as close as possible], part of the same batch

 

I took photos of the cones and some of the bloated vs non-bloated pieces. Not sure if they would help, but can post. I also dropped IMCO an e-mail to see if anyone has had similar issues.

 

My main issue is that the glazes I have available mature a little better at ^6 than ^5, and if I can't nail this down then I may have to switch clay bodies.

 

Any thoughts?

 

Best,

-- MrE

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perkolator    53

I've never worked with that particular IMCO body, but I would call them up since I've never had much luck e-mailing them - and talk to Eric Struck....he should be able to help you with your questions.

 

 

What is your firing schedule for both bisque and glaze? Many times, a change here will solve something like this - like slowing it down or holding during bisque to fully burn out the carbon. I know that Stoneware 1c is a particularly fine clay body made for uber vitreous pottery - so getting that carbon out will take slightly more time than a more porous body.

 

 

I would personally try tweaking the firing first, but I would also try out some of their other clay bodies since they carry so many great clays. Perhaps the 50/50 mix or Navajo Wheel might work for you.

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mregecko    18

I've never worked with that particular IMCO body, but I would call them up since I've never had much luck e-mailing them - and talk to Eric Struck....he should be able to help you with your questions.

 

 

What is your firing schedule for both bisque and glaze? Many times, a change here will solve something like this - like slowing it down or holding during bisque to fully burn out the carbon. I know that Stoneware 1c is a particularly fine clay body made for uber vitreous pottery - so getting that carbon out will take slightly more time than a more porous body.

 

 

I would personally try tweaking the firing first, but I would also try out some of their other clay bodies since they carry so many great clays. Perhaps the 50/50 mix or Navajo Wheel might work for you.

 

 

The bisque firing is to ^05 if I remember correctly, on a medium-speed schedule (Skutt Kiln). I'm thinking it's not a matter of bloating from carbon because it's fine at ^5 (essentially same ramp up / down schedule, just to a slightly higher temperature). It's almost like bloating from overfiring, but the clay is specced just fine for ^6.

 

I'll collect more exact information about the both bisque and glaze firing schedules and post here (and I'll probably give Eric @ IMCO a call too). Thanks for the thoughts!

 

And if all else fails, another clay body may be the trick.

 

-- M

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neilestrick    1,379

Have you confirmed the actual cone in your kiln with witness cones? It could be that your kiln is actually overfiring. I just worked on a couple of Skutts yesterday that are always almost two cones hot.

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mregecko    18

Great news! Got an update from Eric over at IMCO, who was super helpful.

 

It turns out that this clay has a component (Banta) which is tricky at the top end of its vitrification range, ^6... it tends to bloat a lot.

 

The banta is being replaced with a combination of clays in the Stoneware 1-C, and that'll hit shelves in January.

 

In the meantime, if anyone is having this problem with the existing clay, a very slow / hotter bisque firing (Eric recommended to cone 02) will help reduce bloating. Or just fire to ^5.

 

Thanks to everyone who responded to this thread, and especially thanks to Eric at IMCO for his help here.

 

Best,

-- M

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perkolator    53

interesting to know that. kinda makes sense that the banta is the issue because on its own (although very beautiful) it likes to glass out, then bubble and bloat at the ^6 range. just soooo much iron it that clay.

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GMosko    4

Great news! Got an update from Eric over at IMCO, who was super helpful.

 

It turns out that this clay has a component (Banta) which is tricky at the top end of its vitrification range, ^6... it tends to bloat a lot.

 

The banta is being replaced with a combination of clays in the Stoneware 1-C, and that'll hit shelves in January.

 

In the meantime, if anyone is having this problem with the existing clay, a very slow / hotter bisque firing (Eric recommended to cone 02) will help reduce bloating. Or just fire to ^5.

 

Thanks to everyone who responded to this thread, and especially thanks to Eric at IMCO for his help here.

 

Best,

-- M

 

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GMosko    4

Great news! Got an update from Eric over at IMCO, who was super helpful.

 

It turns out that this clay has a component (Banta) which is tricky at the top end of its vitrification range, ^6... it tends to bloat a lot.

 

The banta is being replaced with a combination of clays in the Stoneware 1-C, and that'll hit shelves in January.

 

In the meantime, if anyone is having this problem with the existing clay, a very slow / hotter bisque firing (Eric recommended to cone 02) will help reduce bloating. Or just fire to ^5.

 

Thanks to everyone who responded to this thread, and especially thanks to Eric at IMCO for his help here.

 

Best,

-- M

 

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GMosko    4

Great news! Got an update from Eric over at IMCO, who was super helpful.

 

It turns out that this clay has a component (Banta) which is tricky at the top end of its vitrification range, ^6... it tends to bloat a lot.

 

The banta is being replaced with a combination of clays in the Stoneware 1-C, and that'll hit shelves in January.

 

In the meantime, if anyone is having this problem with the existing clay, a very slow / hotter bisque firing (Eric recommended to cone 02) will help reduce bloating. Or just fire to ^5.

 

Thanks to everyone who responded to this thread, and especially thanks to Eric at IMCO for his help here.

 

Best,

-- M

 

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GMosko    4

I think it is great that you received such fast and honest service from the supplier. I also agree that bisquing higher tends to burn out the volatiles. But ^02??? Wow, good luck trying to glaze any pieces that were bisqued that high. I have trouble even at 03, and must stay at 04 as the highest bisque temp, if I want to have any kind of ease during glazing. Cone 02 for me would be so hard (partially vitrified) that it would not be able to absorb the water from the glaze, making life difficult.

 

I recently had a really rotten batch of low-fire white clay. It didn't bloat, but it caused all my glazes to boil. My only recourse has been to bisque on the high side of 04, but to also do it slowly. I even soak in extreme oxidation for 45 minutes at the end of the fire. It's all about allowing any volatiles to escape BEFORE you glaze.

 

Hope this helps.

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