aaron cortelyou on thu 17 jun 10
A ceramicist visited my school a while back and we got to talking
about the trade. He asked me if I had thrown with clay made from pure
bentonite; I had not. I didn't ask him much about it but now I'm a
little curious. I just mixed up a small 25 lb bag and I'm going to let
it sit for a couple of weeks until the particles are completely
saturated but I have a question until then. What is the maximum cone
this clay can be fired to? It has a melting point of 2642F so I'm not
too worried about ruining a kiln shelf but how much under that would
it be safe to fire it too?
aaron cortelyou on fri 18 jun 10
Unfortunately we store our dry materials in bins and (until now) only
have used 1.5 percent bentonite in our glazes. The bag is long gone,
I've been at the studio for 4 years and haven't refiled the bin in
that time. I did inventory around a year ago and I know there isn't
another bag. I might try to get a hold of clay art center,our
supplier; I'd be surprised if they had more than a couple of types.
On Fri, Jun 18, 2010 at 8:15 PM, wrote:
> Look on the bag - there may be a reference to a company or mine - try to
> also find a product description - then find the company on the internet -
> download the analysis or ask for one.
>
> Or send me the info.
>
> Worth a try!
>
> RR
>
>
>
> Quoting aaron cortelyou :
>
>> damn, as per usual I'm in over my head. I don't have a good analysis.
>> It's just the bentonite the studio I'm a part of has on hand to keep
>> glazes suspended.
>>
>> On Fri, Jun 18, 2010 at 8:01 PM, =3DA0 wrote:
>>>
>>> Hi Aarron,
>>>
>>> If you have a good analysis for that bentonite I may be able to give yo=
=3D
u
>>> some clues.
>>>
>>> RR
>>>
>>>
>>> Quoting aaron cortelyou :
>>>
>>>> A ceramicist visited my school a while back and we got to talking
>>>> about the trade. He asked me if I had thrown with clay made from pure
>>>> bentonite; I had not. I didn't ask him much about it but now I'm a
>>>> little curious. I just mixed up a small 25 lb bag and I'm going to let
>>>> it sit for a couple of weeks until the particles are completely
>>>> saturated but I have a question until then. What is the maximum cone
>>>> this clay can be fired to? It has a melting point of 2642F so I'm not
>>>> too worried about ruining a kiln shelf but how much under that would
>>>> it be safe to fire it too?
>>>>
>>>
>>>
>>>
>>>
>>
>
>
>
>
Ron Roy on fri 18 jun 10
Look on the bag - there may be a reference to a company or mine - try
to also find a product description - then find the company on the
internet - download the analysis or ask for one.
Or send me the info.
Worth a try!
RR
Quoting aaron cortelyou :
> damn, as per usual I'm in over my head. I don't have a good analysis.
> It's just the bentonite the studio I'm a part of has on hand to keep
> glazes suspended.
>
> On Fri, Jun 18, 2010 at 8:01 PM, wrote:
>> Hi Aarron,
>>
>> If you have a good analysis for that bentonite I may be able to give you
>> some clues.
>>
>> RR
>>
>>
>> Quoting aaron cortelyou :
>>
>>> A ceramicist visited my school a while back and we got to talking
>>> about the trade. He asked me if I had thrown with clay made from pure
>>> bentonite; I had not. I didn't ask him much about it but now I'm a
>>> little curious. I just mixed up a small 25 lb bag and I'm going to let
>>> it sit for a couple of weeks until the particles are completely
>>> saturated but I have a question until then. What is the maximum cone
>>> this clay can be fired to? It has a melting point of 2642F so I'm not
>>> too worried about ruining a kiln shelf but how much under that would
>>> it be safe to fire it too?
>>>
>>
>>
>>
>>
>
aaron cortelyou on fri 18 jun 10
damn, as per usual I'm in over my head. I don't have a good analysis.
It's just the bentonite the studio I'm a part of has on hand to keep
glazes suspended.
On Fri, Jun 18, 2010 at 8:01 PM, wrote:
> Hi Aarron,
>
> If you have a good analysis for that bentonite I may be able to give you
> some clues.
>
> RR
>
>
> Quoting aaron cortelyou :
>
>> A ceramicist visited my school a while back and we got to talking
>> about the trade. He asked me if I had thrown with clay made from pure
>> bentonite; I had not. I didn't ask him much about it but now I'm a
>> little curious. I just mixed up a small 25 lb bag and I'm going to let
>> it sit for a couple of weeks until the particles are completely
>> saturated but I have a question until then. What is the maximum cone
>> this clay can be fired to? It has a melting point of 2642F so I'm not
>> too worried about ruining a kiln shelf but how much under that would
>> it be safe to fire it too?
>>
>
>
>
>
Ron Roy on fri 18 jun 10
Hi Aarron,
If you have a good analysis for that bentonite I may be able to give
you some clues.
RR
Quoting aaron cortelyou :
> A ceramicist visited my school a while back and we got to talking
> about the trade. He asked me if I had thrown with clay made from pure
> bentonite; I had not. I didn't ask him much about it but now I'm a
> little curious. I just mixed up a small 25 lb bag and I'm going to let
> it sit for a couple of weeks until the particles are completely
> saturated but I have a question until then. What is the maximum cone
> this clay can be fired to? It has a melting point of 2642F so I'm not
> too worried about ruining a kiln shelf but how much under that would
> it be safe to fire it too?
>
Eric Hansen on fri 18 jun 10
aaron: I was digging bentonite in Oregon. There are swelling bentonites and
non swelling bentonites, then there is loess which can be bentonitic, then
there is loess like what the Great Wall of China is made. If the
bentonite-out-of-the-bag doesn't work try a different source. I'd place you=
r
test tiles in the bisque first (?)
- h -
On Thu, Jun 17, 2010 at 7:51 PM, aaron cortelyou wrote=
:
> A ceramicist visited my school a while back and we got to talking
> about the trade. He asked me if I had thrown with clay made from pure
> bentonite; I had not. I didn't ask him much about it but now I'm a
> little curious. I just mixed up a small 25 lb bag and I'm going to let
> it sit for a couple of weeks until the particles are completely
> saturated but I have a question until then. What is the maximum cone
> this clay can be fired to? It has a melting point of 2642F so I'm not
> too worried about ruining a kiln shelf but how much under that would
> it be safe to fire it too?
>
douglas fur on sat 19 jun 10
Arron
Now why wasit you're trying this? If my memory is correct (always a
dangerous supposition)
bentonite is a montmorrilonite clay mineral. This type of clay has
half-again as much SiO2 as kaolinite clays so when they're fired you have
more free silica (not a rallying cry from the 70's) an hence more dunting i=
n
cooling both bisque and glaze fires.
But you've got it ready to go, so try it out and see what happens.
DRB
Seola Creek
John Post on sat 19 jun 10
Aaron,
You aren't in over your head, you are simply in the middle of a good =3D20
experiment. If you already know the outcome of something, then it's =3D20
not an experiment.
Here's my thinking on this. Lowfire white clay bodies which are half =3D20=
=3D
talc are designed to work in the cone 06-04 range, which is =3D20
approximately 1800=3DB0 - 1900=3DB0 degrees Fahrenheit. These lowfire whit=
e =3D
=3D20
bodies are half flux, and they don't melt down and run over the =3D20
shelves at those temperatures. If you fire them a few cones higher, =3D20
they will start to melt and deform.
Your bentonite will likely be able to withstand firing to bisque =3D20
temperatures, so I would start there and see how porous and dense it is.
I just finished processing a bunch of local earthenware clay with my =3D20
elementary students and am in the process of drying some of it out. =3D20
If I want to find out what this clay is like at cone 6 which equals =3D20
2187=3DB0 Fahrenheit in my kiln, I would simply make a small bowl and fire =
=3D
=3D20
it on a clay tile or broken piece of kiln shelf in case of meltdown.
I don't have an analysis for this clay, it's not necessary to work =3D20
with it. I just fire it at different temperatures in my kilns to see =3D20=
=3D
how it behaves. I know from a line blend experiment that I did, that =3D20=
=3D
if I mix 90% local clay with 10% unwashed wood ash, I get a nice =3D20
yellow brown glaze, using all free materials from mother nature. I =3D20
like to use this glaze with my students because I can show them the =3D20
two raw materials, explain to them where I got them and then tell them =3D2=
0=3D
how early potters figured things out the same way.
John Post
Sterling Heights, Michigan
:: cone 6 glaze website :: http://www.johnpost.us
:: elementary art website :: http://www.wemakeart.org
:: youtube channel :: http://www.youtube.com/user/MrPostArtTeacher
On Jun 18, 2010, at 11:04 PM, aaron cortelyou wrote:
> damn, as per usual I'm in over my head. I don't have a good analysis.
> It's just the bentonite the studio I'm a part of has on hand to keep
> glazes suspended.
Snail Scott on sun 20 jun 10
On Jun 17, 2010, at 6:51 PM, aaron cortelyou wrote:
> A ceramicist visited my school a while back and we got to talking
> about the trade. He asked me if I had thrown with clay made from pure
> bentonite...
I'm messed around with dirt from the playa flats
in Nevada - very high alkali, of course, but very
high in bentonite as well. (About 15%, though;
very far from 100%.) Bizarrely squishy, and
almost 20% shrinkage just from wet to dry.
Just about anything is worth an experiment!
-Snail
Lee Love on sun 20 jun 10
On Sun, Jun 20, 2010 at 2:02 PM, aaron cortelyou wrot=
=3D
e:
> through the quartz inversion both up and down. If it's anything
> interesting I'll post a link to the final product. Somebody with skill
> might be able to produce something interesting with this clay.
Slow cooling increases crystal formation. Mick Cassion crash cooled
his high silica clay body to 1100*C to prevent dunting. So does my
friend in Mashiko, Euan Craig because of his high silica "half
porcelain." I did it in my woodkiln to enhance red color in high
alumina glazes.
--
Lee, a Mashiko potter in Minneapolis
http://mingeisota.blogspot.com/
=3D93Observe the wonders as they occur around you. Don't claim them. Feel
the artistry moving through and be silent.=3D94 --Rumi
aaron cortelyou on sun 20 jun 10
Thanks everyone for you terrific advice. I particularly liked the
advice of making a "cone" out the material to determine it's fire temp
by seeing when it starts to slump. I'll use this trick a lot since I
like to experiment with local materials and unusual clay bodies. I
also have around 50 fired slabs that I fire suspicious work on, I'll
make use of them.
I tried yesterday throwing with this stuff and it's bazaar. It's
really squishy but holds it's form extremely well. It feels like a
combination of thick rubber and jello. When you finish a pot you can
flick it and it vibrates like rubber. You can throw very tall and then
do something crazy like making a thin rim that goes out at a 90 degree
angle for an inch and it will support itself. It I were better at the
wheel I could make some unusual pots with this stuff. On the down side
it's not "stretchy" at all. You can't throw a cylinder and widen a rim
to make a bowl. You could make a cup no problem but anything beyond
that is impossible. I'm bisquing it now with a cycle that slows
through the quartz inversion both up and down. If it's anything
interesting I'll post a link to the final product. Somebody with skill
might be able to produce something interesting with this clay.
On Sat, Jun 19, 2010 at 1:14 PM, douglas fur <23drb50@gmail.com> wrote:
> Arron
> Now why wasit you're trying this? If my memory is correct (always a
> dangerous supposition)
> bentonite is a montmorrilonite clay mineral. This type of clay has
> half-again as much SiO2 as kaolinite clays so when they're fired you have
> more free silica (not a rallying cry from the 70's) an hence more dunting=
in
> cooling both bisque and glaze fires.
> But you've got it ready to go, so try it out and see what happens.
> DRB
> Seola Creek
Ron Roy on mon 21 jun 10
Hi Lee,
Casson probably did that to prevent to much cristobalite from forming =3D20
- cristobalite can certainly lead to dunting.
RR
Quoting Lee Love :
> On Sun, Jun 20, 2010 at 2:02 PM, aaron cortelyou wr=
o=3D
te:
>
>> through the quartz inversion both up and down. If it's anything
>> interesting I'll post a link to the final product. Somebody with skill
>> might be able to produce something interesting with this clay.
>
> Slow cooling increases crystal formation. Mick Cassion crash cooled
> his high silica clay body to 1100*C to prevent dunting. So does my
> friend in Mashiko, Euan Craig because of his high silica "half
> porcelain." I did it in my woodkiln to enhance red color in high
> alumina glazes.
> --
> Lee, a Mashiko potter in Minneapolis
> http://mingeisota.blogspot.com/
>
> =3DE2=3D80=3D9CObserve the wonders as they occur around you. Don't claim =
them. F=3D
eel
> the artistry moving through and be silent.=3DE2=3D80=3D9D --Rumi
>
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