Maurice Weitman on mon 15 oct 07
At 18:41 -0700 on 10/15/07, Bob Hanlin wrote:
>I've been using cone 5 BMix for the past three years, firing it to
>cone 6 oxidation. In my last two firings the pots on the top shelf
>have bloat. I fire to cone6 (Yes, I know it's cone 5 clay...and
>when I asked Laguna where cone 5 BMix was vitrious, they said "cone
>6", and did not offer any cautions about the 1 Cone over firing.
>The problem occurs no matter what glaze in on the pieces, and it
>only happens on the top shelf.
>I have an 1018-3" Skutt Kiln with electronic controller. My firing
>schedule is:
>Room Tem to 220 DegF.....100 DegF/Hr,
>Hold for 1 Hour
>From 220DegF to 2000 DegF.....300 DegF/Hr
>From 2000 DegF to 2232 DegF...200 DegF/Hr
>Hold for 20 minutes
>Cool without control
Hello, Bob,
I haven't got much experience with B-Mix 5, but I do have some
thoughts and questions for you:
First of all, Laguna's cone ratings are not exactly uhhh...
definitive... their literature often says something like: "... most
Laguna clays have a fairly broad firing range." (Sets my teeth on
edge.) They now list B-Mix 5 under cone 6 clay bodies, so go figure.
My first reaction is to ask "what's changed since the problem
started?" Assuming it's the same body, glazes, and procedures, what
I'm left with is the amount of heat work those pots are getting.
Do you use witness cones on each shelf? (If not, I think you should
to really know what's going on.) If so, what do they report? If all
shelves are the same, well... never mind. Just hit the delete key...
it's your best friend.
Otherwise, it's possible that (one or both of) your thermocouples
have drifted enough to make a difference.
From your firing schedule, it appears that you don't single-fire, so
to what cone do you fire your biscuit?
It's possible that your bisc'd ware hasn't had enough heat work to
burn out all its carbonaceous material which could cause bloating
during your glaze firing.
I'm pretty sure Skutts use multiple thermocouples (I know their
controller is capable of using three zones -- your kiln probably has
two), so it's possible that the top 'couple is getting flaky.
If none of the above, well, blame it on the same forces at play
against the Yankees.
Regards,
Maurice, still sniffin' and honkin' while enjoying Cleveland's win
and what appears to be a Colorado sweep.
Bob Hanlin on mon 15 oct 07
I've been using cone 5 BMix for the past three years, firing it to cone 6 o=
xidation. In my last two firings the pots on the top shelf have bloat. I =
fire to cone6 (Yes, I know it's cone 5 clay...and when I asked Laguna wher=
e cone 5 BMix was vitrious, they said "cone 6", and did not offer any cauti=
ons about the 1 Cone over firing. The problem occurs no matter what glaz=
e in on the pieces, and it only happens on the top shelf. =0A=0AI have an =
1018-3" Skutt Kiln with electronic controller. My firing schedule is:=0A=
=0ARoom Tem to 220 DegF.....100 DegF/Hr,=0AHold for 1 Hour=0AFrom 220DegF t=
o 2000 DegF.....300 DegF/Hr=0AFrom 2000 DegF to 2232 DegF...200 DegF/Hr=0AH=
old for 20 minutes=0ACool without control=0A=0AI'm writing this in case any=
of you are having or have had this problem and hope for a solution or recc=
omendatio. If Laguna folk see this...I hope they will offer something.=0A=
=0A=0ABob Hanlin=0AOklahoma City=0AIt's starting to cool down on the plains=
=0A=0Abobhanlin@sbcglobal.net
Carole Fox on tue 16 oct 07
On Mon, 15 Oct 2007 18:41:44 -0700, Bob Hanlin
wrote:
>I've been using cone 5 BMix for the past three years, firing it to cone 6
oxidation. In my last two firings the pots on the top shelf have bloat...
Bob - I frequently fire Laguna ^5 BMix to shelf ^6 (halfway down) with no
problem, and have fired to ^6 flat occasionally also with no problem. I
have never seen bloating with this clay body, although I have had a few
pieces dunt with thick glaze. I use the Eastern version of this clay
body - the Western version may behave differently. I fire a manual kiln,
so I always use shelf cones. Sounds to me like your kiln's top section is
firing hot (you didn't say whether you used shelf cones), rather than a
problem with the clay body.
Carole Fox
Dayton, OH
Brenda Phillips on tue 16 oct 07
I have been using Laguana's BMix 5 for years and have experienced bloating,
maybe a piece every other firing and it doesn't seem to matter which shelf
the piece is on. I use glazes and firing schedule from MC6G, but only going
to 2190deg.F and my cone 7 bends. I have a Skutt 1027-3". I'm hoping for a
solution or recommendation, too.
Brenda Phillips
Manchester, CA where it is raining at last!
----- Original Message -----
From: "Bob Hanlin"
To:
Sent: Monday, October 15, 2007 5:41 PM
Subject: Laguna Cone 5 BMix...
I've been using cone 5 BMix for the past three years, firing it to cone 6
oxidation. In my last two firings the pots on the top shelf have bloat. I
fire to cone6 (Yes, I know it's cone 5 clay...and when I asked Laguna where
cone 5 BMix was vitrious, they said "cone 6", and did not offer any cautions
about the 1 Cone over firing. The problem occurs no matter what glaze in
on the pieces, and it only happens on the top shelf.
I have an 1018-3" Skutt Kiln with electronic controller. My firing schedule
is:
Room Tem to 220 DegF.....100 DegF/Hr,
Hold for 1 Hour
From 220DegF to 2000 DegF.....300 DegF/Hr
From 2000 DegF to 2232 DegF...200 DegF/Hr
Hold for 20 minutes
Cool without control
I'm writing this in case any of you are having or have had this problem and
hope for a solution or reccomendatio. If Laguna folk see this...I hope they
will offer something.
Bob Hanlin
Oklahoma City
It's starting to cool down on the plains
bobhanlin@sbcglobal.net
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Jon Pacini on tue 16 oct 07
Greetings All ---Hi Bob--you wrote--
I've been using cone 5 BMix for the past three years, firing it to cone 6 o=
xidation. In my last two firings the pots on the top shelf have bloat. I =
fire to cone6 (Yes, I know it's cone 5 clay...and when I asked Laguna where=
e cone 5 BMix was vitrious, they said "cone 6", and did not offer any cauti=
ons about the 1 Cone over firing. The problem occurs no matter what glaz=
e in on the pieces, and it only happens on the top shelf.
We've been making this clay for going on 15+ years and have may potters who
fire this clay to even higher temperatures than ^6.
By vitreous I'd guess you were looking for a temperature where it's porosity
drops to under 2%. this is generally about as non-porous as you want a
stoneware to get. some potters might argue 1% but that's just splitting
hairs. At ^5 B Mix 5 is rated at approx 2.5%. At ^6 it's approaching 1.5%
There are a couple of contributing factors to bloating. Not just
temperature. First, gasses have to be present and trapped inside the body.
Then the body has to be soft enough to allow the gasses to expand, but fused
enough not to let them escape. With many White bodies the clay/glaze
interface layer can become a barrier to gasses escaping.
To overcome this I generally recommend a bisque firing to at least ^04 with
a good soak at the end. If you've got a tightly packed bisque kiln I'd start
slowing the firing down about 100*f from the end and proceed at 50* and hr
and then the last 25* over the last hour. Electric Kilns are notorious for
not firing evenly top to bottom and even from the edge to the center with
the larger diameter ones. Slowing down at the end allows the heat to
equalize over the entire kiln and throughout all the ware.
I'd also be tempted to put witness cones throughout the kiln just to make
sure what you think is happening is really happening. The new electronic
controllers are a great tool, but electronics and high heat are not good
bedfellows and things can get out of whack quite rapidly and unexpectedly.
And if you're convinced it's the clay ---send some of your clay in to me
along with the batch number and I'll check it out.
Best regards,
Jon Pacini
Clay Manager
Laguna Clay Co
Gayle Bair on tue 16 oct 07
Hi Carol,
Was the clay well wedged?
When I found a couple of B-Mix pieces with bloating
I realized they were air bubbles & I had not wedged the clay well enough.
I just used a bag that gave me a lot of trouble... with lots of air bubbles
in my pieces as I was throwing.
I did my usual wedging and still had trouble. I thought
I was really losing it for a while until I checked the clay right out
of the bag! Finally I cut into the bagged clay and there they were.... lots
of air pockets!
Note I have fired B-Mix to ^7 but had pinhole issues & it's probably not
recommended
as it may be over vitrified.
Gayle Bair
Bainbridge Island, WA
Tucson, AZ
http://claybair.com
On Mon, 15 Oct 2007 18:41:44 -0700, Bob Hanlin
wrote:
>I've been using cone 5 BMix for the past three years, firing it to cone 6
oxidation. In my last two firings the pots on the top shelf have bloat...
Bob - I frequently fire Laguna ^5 BMix to shelf ^6 (halfway down) with no
problem, and have fired to ^6 flat occasionally also with no problem. I
have never seen bloating with this clay body, although I have had a few
pieces dunt with thick glaze. I use the Eastern version of this clay
body - the Western version may behave differently. I fire a manual kiln,
so I always use shelf cones. Sounds to me like your kiln's top section is
firing hot (you didn't say whether you used shelf cones), rather than a
problem with the clay body.
Carole Fox
Dayton, OH
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5:55 PM
William & Susan Schran User on tue 16 oct 07
On 10/15/07 9:41 PM, "Bob Hanlin" wrote:
> I've been using cone 5 BMix for the past three years, firing it to cone 6
> oxidation. In my last two firings the pots on the top shelf have bloat. I
> fire to cone6 (Yes, I know it's cone 5 clay...and when I asked Laguna where
> cone 5 BMix was vitrious, they said "cone 6", and did not offer any cautions
> about the 1 Cone over firing. The problem occurs no matter what glaze in on
> the pieces, and it only happens on the top shelf.
>
> I have an 1018-3" Skutt Kiln with electronic controller.
Apparently the top of your kiln is firing hotter than other sections.
Do you fire with cones or rely on the controller?
Your schedule indicates a slow ramp to 2232, then a 20 minute hold.
Have you checked this firing schedule against cones?
May be going beyond ^6.
--
William "Bill" Schran
wschran@cox.net
wschran@nvcc.edu
http://www.creativecreekartisans.com
Jason Hooper on wed 17 oct 07
Hi Bob,
I've been getting small individual bloats - abut 1/4 - 1/2 inch across - from my
latest batch of BMix. I've also had a couple of small pop-outs in the bisque
firing. I think the problem I'm seeing is from impurities in the clay. I picked
a grain out of the clay yesterday when I was throwing - looked like a 1/8th
piece of translucent crystal.
It's become a little annoying as I seem to get one bloated spot on most pots of
6# or bigger.
I fire to about cone 5 1/2, cone 6 at hottest.
cheers,
Jason
Bob Hanlin wrote:
> I've been using cone 5 BMix for the past three years, firing it to cone 6
> oxidation. In my last two firings the pots on the top shelf have bloat. I
> fire to cone6 (Yes, I know it's cone 5 clay...and when I asked Laguna where
> cone 5 BMix was vitrious, they said "cone 6", and did not offer any cautions
> about the 1 Cone over firing. The problem occurs no matter what glaze in
> on the pieces, and it only happens on the top shelf.
>
> I have an 1018-3" Skutt Kiln with electronic controller. My firing schedule
> is:
>
> Room Tem to 220 DegF.....100 DegF/Hr, Hold for 1 Hour From 220DegF to 2000
> DegF.....300 DegF/Hr From 2000 DegF to 2232 DegF...200 DegF/Hr Hold for 20
> minutes Cool without control
--
Jason Hooper
http://www.jjhooper.com
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