[meisie]

I am curious why I have bubbles in this bowl. It's a cone 6 laguna clay, I wedged and re wedged and I use the clay twice. The first time the bowl wasn't what I wanted. Under glazed and then bisqued to cone 04 and then clear glaze and fired to cone 6. The kiln is small and the bowls I had were fairly large so one on the bottom, one in the middle and 4 pieces on the top. I did not have a hold time. Could this be that many air bubbles expanding? Or is it something else.
Thanks for any help
Renee

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[neilestrick]

Looks like bloating to me. Did your kiln over-fire? Are you sure your clay can go as high as you did?

[Marcia Selsor]

I agree with Neil. It looks like classic bloating from over firing the kiln. It is odd since you fired it once to ^6 before the last firing. What did the cones look like?

Marcia

[yedrow]

I too agree with Neil and Marcia. It seems odd since you fired it twice. I think too that you may see if you are firing your ware too fast. If you go through the 1100 to 1800 zone too fast you may not sufficiently outgas the volatiles. Also, if you go too fast the bubble with rise from the center of the clay, but if you are over-firing it is likely the bubble will rise from the surface of the clay.

[Mark C.]

Bloating for sure-Look up bloating
Several factors can cause this-over firing is one twice firing can do it as well.There are others as well . It can even be the clay came from a bad batch(Laguna will always contest this point) .I'm not thinking air bubbles but instead the clay body is coming apart-when you break this bowl you can see it in the cross section of one of those spots usually.
I once shipped 100#s of bloated work back to Laguna that had boated just to feel better.It was one of my better moments as They all know me since then and fixed the body problems at least for some time.
Mark

[LilyT]

Hi, Miesie,

Agree with the experts that this is bloating.

Which Laguna clay is this? I have had Laguna clays bloat despite being
fired to or one cone below their stated range. I am currently sadly working through
a ton of B-mix that does exactly what you picture. I just wedge it
into something else and it's not so unstable - big pain in the tuckus.
The remainder of the batch will be going into my pizza oven (as the oven itself,
not the pizza) I will not order from Laguna again, not very helpful
with quality of product :-(. (previous ton had metal bits in it, they
just denied it.)

Interesting thing I noticed with my bloating... if I down fire slowly (100F/hr to
1500), the ugly bubbles collapse and reseal, though a little criss-cross
hatchmark is slightly visible. The profile of the ware is normal and the
thickness of the ware at the defect returns to normal. In a
more textured glaze it can almost pass for an interesting feature...
Has anyone else noticed this? You could almost use it to decorate with,
some of the pieces have a LOT of little bloats.

You could try to do that if you want to do something with the piece, it
is otherwise pretty hard to ignore the bloats.

-Lily

[LilyT]

Mark C., on 12 July 2012 - 11:22 PM, said:

Bloating for sure-Look up bloating
Several factors can cause this-over firing is one twice firing can do it as well.There are others as well . It can even be the clay came from a bad batch(Laguna will always contest this point) .I'm not thinking air bubbles but instead the clay body is coming apart-when you break this bowl you can see it in the cross section of one of those spots usually.
I once shipped 100#s of bloated work back to Laguna that had boated just to feel better.It was one of my better moments as They all know me since then and fixed the body problems at least for some time.
Mark

Heehee. I will keep your strategy in mind for dealing with Laguna...

-Lily

[clay lover]

yedrow, on 12 July 2012 - 11:33 PM, said:

I too agree with Neil and Marcia. It seems odd since you fired it twice. I think too that you may see if you are firing your ware too fast. If you go through the 1100 to 1800 zone too fast you may not sufficiently outgas the volatiles. Also, if you go too fast the bubble with rise from the center of the clay, but if you are over-firing it is likely the bubble will rise from the surface of the clay.

Yedrow, I am very interested in your comment. Although I am not having bloating, I am interested in learning all I can about not firing any longer that necessary. Could you expound on what you feel is 'too fast'?
I am quite happy to take as long as it takes, but why take longer?
Currently for ^6 I am firing
200*/hr to 205,
4oo*/hour to 1900
110*/hr to 2195 with a 20 minute soak, then down firing slowly to off at 1600*
My cone are good and even through the kiln. Glazes look good.

Any suggestions for improved efficiency wqill be appreciated and considered.
Other than slight pinholing occationally, I am not having problems.

How slow to go?

[meisie]

Thank you all. I read a bit about bloating and I think because I didn't have as many pieces in my kiln that it may have fired a bit faster on the bisque. According to the article that would cause bloating on the final firing. I will make a new bowl and bisque fire slowly and hopefully that will be one step in preventing it. I had two boxes of this clay and am down to my last 20 lbs, this is the first time it's been a problem. Not having a totally full kiln is the only difference between these bowls and several others I have done using the same clay.

According to the Laguna web site bloating originates in the bisque firing and then manifests itself during the glaze firing. I guess that goes along with my difference in a less full kiln and a faster fire. Oh well now I have to tell the woman I'm making them for that something happened and it will be August......





Thanks for pointing me in the right direction.
Renee

[meisie]

Mark C., on 13 July 2012 - 01:22 AM, said:

Bloating for sure-Look up bloating
Several factors can cause this-over firing is one twice firing can do it as well.There are others as well . It can even be the clay came from a bad batch(Laguna will always contest this point) .I'm not thinking air bubbles but instead the clay body is coming apart-when you break this bowl you can see it in the cross section of one of those spots usually.
I once shipped 100#s of bloated work back to Laguna that had boated just to feel better.It was one of my better moments as They all know me since then and fixed the body problems at least for some time.
Mark

You shipped your bloated work to Laguna? I'll bet they liked that.... ?
http://www.lagunacla...blackcoring.php this is what came up as soon as I googled "bloating in ceramics"

[neilestrick]

I don't totally agree with Laguna's theories on bloating. I don't care how slowly you bisque- if you over-fire stoneware it can bloat. I have never seen a stoneware pot of normal thickness slump from over-firing without it bloating. Too hot equals bloating. I also disagree with their contention that a body that bloats needs to be fired differently, not reformulated. That's putting the solution on the customer, instead of addressing the issue themselves. Any clay body that needs to be fired in a special way to prevent bloating should not be sold commercially. If it says cone 6, it should work under any fairly 'normal' firing situation.

[yedrow]

clay lover, on 13 July 2012 - 07:16 AM, said:

yedrow, on 12 July 2012 - 11:33 PM, said:

I too agree with Neil and Marcia. It seems odd since you fired it twice. I think too that you may see if you are firing your ware too fast. If you go through the 1100 to 1800 zone too fast you may not sufficiently outgas the volatiles. Also, if you go too fast the bubble with rise from the center of the clay, but if you are over-firing it is likely the bubble will rise from the surface of the clay.

Yedrow, I am very interested in your comment. Although I am not having bloating, I am interested in learning all I can about not firing any longer that necessary. Could you expound on what you feel is 'too fast'?
I am quite happy to take as long as it takes, but why take longer?
Currently for ^6 I am firing
200*/hr to 205,
4oo*/hour to 1900
110*/hr to 2195 with a 20 minute soak, then down firing slowly to off at 1600*
My cone are good and even through the kiln. Glazes look good.

Any suggestions for improved efficiency wqill be appreciated and considered.
Other than slight pinholing occationally, I am not having problems.

How slow to go?

First, I may have expertise at throwing pots, but I'm not one of the experts on firing kilns, my apologies if I sounded otherwise.

Anyway, I think firing somewhat slow is best. I bisque fire at about 180˚/hr. above 212˚. Clays are different and some seem to me to have more easily volatilized materials in them, sulfer, carbonates, detritus, etc. I think its a good idea get as much of that out as possible. Once the clay-glaze boundary is established, gasses won't easily escape. Then, when the clay softens as it vitrifies, the pressurized air can bulge up. Also, when the body is more open oxygen can get in and oxidize the volatiles. If the walls of the ware are thick (I throw about 1/8th inch, averaged top to bottom, but newer potters throw twice that thick or more) then the ware must be fired slower since there is more mass for volatiles and oxygen to move through. I glaze fire at about 300˚/hr with slow drop in heat edit:[during cool down] from 1900˚ to 1500˚. Note too, in an electric kiln, the heat is moved primarily by radiation and a quickly fired kill can have quite a lag between the ware that is close to the elements and that which is in the center, in the "shadow" of other ware. This is especially true in a wider kiln.

That being said, I think the problem is probably over-firing and that it may well be the supplier. I've only used Laguna clay once, and my results were pretty bad, and their customer service was worse. They appeared to have no idea why I was having the problem and appeared to have no interest in solving it. I've said elsewhere, Standard clay has the best clay I've ever thrown with, by far. And, your local supplier will probably be able to handle your needs at a good cost.

[LilyT]

neilestrick, on 13 July 2012 - 10:26 AM, said:

I don't totally agree with Laguna's theories on bloating. I don't care how slowly you bisque- if you over-fire stoneware it can bloat. I have never seen a stoneware pot of normal thickness slump from over-firing without it bloating. Too hot equals bloating. I also disagree with their contention that a body that bloats needs to be fired differently, not reformulated. That's putting the solution on the customer, instead of addressing the issue themselves. Any clay body that needs to be fired in a special way to prevent bloating should not be sold commercially. If it says cone 6, it should work under any fairly 'normal' firing situation.

I am not an expert but I was also taught this about bloating, Neil, and my limited
experience echoes yours. I have also felt that Laguna's problems

may not be simply due to a marginal recipe, but inconsistencies from batch to
batch. When the local college orders clay, I always buy a couple bags
from each batch, and "b-mix' behaves quite variably from batch to batch (when fired
in an electric kiln with one of the automated programs). (I know a lot of people
feel that b-mix is not very good clay, but when soft, it is easy and comfortable
for beginners to throw and at one time I taught enough little kids and their
parents that I stocked up. And I love how it feels like smooth butter.)

[Mark C.]

A long time ago I got most of my clay from a mega supplier called Westwood Clay Co. circa 1970s-1980s This Company never paid any attention to us little potters when there clay went bad-we where always at fault so I got feed up and looked around some-There was a small clay company down south in LA area near Westwood that I heard made good clay it was called Laguna clay co-The owners Dad lived near me and when he sold out his stuff and moved I bought some of it-During that time I decided to see this clay company and meet his son John Brooks-It was a small place in Santa Ana at that time about 14 hours drive south of me. I switched to their porcelains after a tour of the plant by John Brooks. I used Dave’s Porcelain for many years in my production studio then I starting to have problems mostly bloating and some shivering-I was an old time experienced user and did not take its my fault well-yes I raised my bisque temperatures and still I lost huge amounts due to bloating all the while the techs said it was me and every one I know who used this clay also had these woes. After firing three car kiln loads at Xmas I and getting nowhere with John on this issue I just sent all 3 loads.

After a few long stonewall talks to John Brooks I packed up 3 whole 35 cubic foot car kiln loads in 3 huge TV boxes and shipped them UPS to Johns upstairs office-I did not pack these to service just tumble stacked 3 whole kiln loads in large boxes with zero padding and drove a full large truck off to ups the bill back then in the 80’s was over 100$ to ship about 150#. I felt great as this amount of work really showed what the crap was going on. After many months of tossing their stuff in the trash I sent it all to the top man. It was liberating and really pissed him off but you see I said how do you think I feel after making all that work and having it bloat- my time my glazing and trimming my gas my sweat -It got thru and years later at a workshop there clay man told me that story was legend at Laguna as john had to pack over 100 #s of shards down stairs to dump them.

I feel good just thinking about the story warms my heart

You see in this world you should be held accountable for good bad or inferior work-clay is our life blood and no matter how I fired it bloated-it was an ingredient problem on the manufacturing side and we all knew it.

They know it but would never admit it. Nowadays I have a good rapport with all of them but we all know where we stand-They need potters like me and I need clay makers like them. Now I have over 25 years of Dave's under my belt and they are having massive issues with B-Mix and its not getting fixed fast enough I'm told-I do not use b-mix but my potter friends do and are switching bodies till Laguna gets it right again

In the clay business things can change very quickly and not always for the better.

So when it comes to the dogma on bloating from Laguna take it with a large grain of salt.

Mark Cortright

[meisie]

Mark C., on 14 July 2012 - 02:31 AM, said:

A long time ago I got most of my clay from a mega supplier called Westwood Clay Co. circa 1970s-1980s This Company never paid any attention to us little potters when there clay went bad-we where always at fault so I got feed up and looked around some-There was a small clay company down south in LA area near Westwood that I heard made good clay it was called Laguna clay co-The owners Dad lived near me and when he sold out his stuff and moved I bought some of it-During that time I decided to see this clay company and meet his son John Brooks-It was a small place in Santa Ana at that time about 14 hours drive south of me. I switched to their porcelains after a tour of the plant by John Brooks. I used Dave’s Porcelain for many years in my production studio then I starting to have problems mostly bloating and some shivering-I was an old time experienced user and did not take its my fault well-yes I raised my bisque temperatures and still I lost huge amounts due to bloating all the while the techs said it was me and every one I know who used this clay also had these woes. After firing three car kiln loads at Xmas I and getting nowhere with John on this issue I just sent all 3 loads.

After a few long stonewall talks to John Brooks I packed up 3 whole 35 cubic foot car kiln loads in 3 huge TV boxes and shipped them UPS to Johns upstairs office-I did not pack these to service just tumble stacked 3 whole kiln loads in large boxes with zero padding and drove a full large truck off to ups the bill back then in the 80’s was over 100$ to ship about 150#. I felt great as this amount of work really showed what the crap was going on. After many months of tossing their stuff in the trash I sent it all to the top man. It was liberating and really pissed him off but you see I said how do you think I feel after making all that work and having it bloat- my time my glazing and trimming my gas my sweat -It got thru and years later at a workshop there clay man told me that story was legend at Laguna as john had to pack over 100 #s of shards down stairs to dump them.

I feel good just thinking about the story warms my heart

You see in this world you should be held accountable for good bad or inferior work-clay is our life blood and no matter how I fired it bloated-it was an ingredient problem on the manufacturing side and we all knew it.

They know it but would never admit it. Nowadays I have a good rapport with all of them but we all know where we stand-They need potters like me and I need clay makers like them. Now I have over 25 years of Dave's under my belt and they are having massive issues with B-Mix and its not getting fixed fast enough I'm told-I do not use b-mix but my potter friends do and are switching bodies till Laguna gets it right again

In the clay business things can change very quickly and not always for the better.

So when it comes to the dogma on bloating from Laguna take it with a large grain of salt.

Mark Cortright

I generally take everything with a grain of salt. Cynic that I am. Awesome story I love it!! I would love for this to be the clay's fault and not mine but I am fairly inexperienced and there is this doubt in my mind. The next firing will certainly tell I suppose.

[LilyT]

"You see in this world you should be held accountable for good bad or inferior work"


Mark,
I am probably getting us way off topic now, however your comment above really
hit home and I just had to comment on it. Your story, legendary now, is so
heartwarming because the right person was finally held accountable. Accountability
really is key to everything, but sadly it doesn't always arise where it should.
I admire your persistent and creative chutzpah in finding a way to enforce
it when the usual channels didn't work. I will enjoy sharing your story with others
because of the point it brings home, and also to give some perspective on
the problems with b-mix. (Plus, lol, I am not above enjoying the story because of
my own personal frustrations, too)
-Lily