Taylor Hendrix on wed 13 feb 08
Howdy folks,
I'm starting about 9 months of kitchen/garage remodeling, but I'm
trying to keep my hand in.
My next clay project now that the pottery sale is over is to develop
some over/under glaze-engobe-slip combinations that work well at cone
6 OX. I've had two Gerald Rowan CM articles from the 80's just burning
a hole in my glaze notebook and I'm ready to try some of the
suggestions.
In a Dec 1986 article (pp. 74-45), "Cone 06 - 6 Vitreous Engobes",
Rowan talks of Bentonite B "a very plastic Texas clay with an
alumina-silica ratio of 1 to 4.5...." I've looked on digitalfire,
googled, and even went to the Milwhite website, but I can't really
find info on Bentonite B. Digitalfire does reference BentoLite B but
there is very little difference between that and generic bentonite
entry.
Rowan writes that "a mixture of 25 parts ball clay and 5 parts
bentonite may be substituted for 30 parts Bentonite B", so I'm really
curious as to how this Bentonite B is different from generic
bentonite.
One further question: Because Rowan's engobes are "dense and vitreous
at cone 06", will that present a problem for me when I bisque green
ware plus the engobes to 04? Will I need to watch out for arrested
burn out at bisque or cooling dunts at 04? I will be trying to wire
that small test kiln I scored awhile back for this project.
Peace out, y'all,
--
Taylor, in Rockport TX
http://wirerabbit.blogspot.com
http://wirerabbitpots.blogspot.com
http://www.flickr.com/photos/wirerabbit/
Neon-Cat on thu 14 feb 08
Taylor, "Bentonite B" was sometimes used to refer to Calcium Bentonite =
(also called Southern Bentonite or Mississippi Bentonite or Calcium =
Montmorillonite). Calcium Bentonite has a much lower swelling capacity =
than the "generic" swelling Sodium Bentonite we use most of the time in =
clay, glazes, slips, and engobes. The exchange formula given in the =
Rowan article might get you close to Bentonite B but if I wanted to =
experiment I'd order Calcium Bentonite from one of the many clay =
suppliers in Texas and adjacent states or purchase some from a chemical =
supplier if ceramic suppliers don't carry this form of Bentonite.=20
My latest part-time craze is working with Blue Clay, a locally dug dry, =
clean (debris-free) Calcium Montmorillonite. It works fairly well with =
no additions, compacting nicely to form very hard, smooth, dense, and =
strong leatherhard and dry statuettes (Calcium Bentonite clays are known =
to have good green strength). Screening the raw clay abrasively causes =
it to turn into fine powder that readily mixes with water. There is =
minimal shrinkage from wet to dry. This morning my first piece went into =
the kiln for bisque (about Cone 05). It should do well and fire light =
orange (I'll find out Saturday morning and can let you know if my piece =
went totally South). In my neck of the woods Calcium Bentonite usually =
has an iron content of 2.0 - 2.5%. I'd be happy to send you a bag or =
small box of my Blue Clay for your experiments. Any more than this and =
I'll have to saddle my shepherd to help me pack it out. Or, send me the =
Rowan recipes and I'll try a few on something here; my pieces will need =
some color and/or highlights. =20
=20
If recipes contain Soda Ash you need to be aware that Calcium Bentonite =
may then form a sodium-exchanged version of Bentonite. Although =
sodium-exchanged Bentonites do not have as high a swelling capacity as =
the natural Sodium Bentonites any increase in swelling might cause =
problems in a clay body, glaze, etc.=20
Of possible interest to cat owners: traditional cat litter is granular =
Calcium Bentonite. Scoopable cat litter is a combination of granular =
Calcium Bentonite with added Sodium Bentonite so that the resulting =
scoopable litter clumps when wetted enabling the happy kitty owner to =
easily and quickly remove any hard clumps from their cat's litter box.
Marian
Neon-Cat Devon Rex & Ceramics
neoncat@flash.net
http://www.neon-cat.com/
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG]On Behalf Of Taylor =
Hendrix
Sent: Wednesday, February 13, 2008 12:00 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Bentonite-B and Rowan article
Howdy folks,
I'm starting about 9 months of kitchen/garage remodeling, but I'm
trying to keep my hand in.
My next clay project now that the pottery sale is over is to develop
some over/under glaze-engobe-slip combinations that work well at cone
6 OX. I've had two Gerald Rowan CM articles from the 80's just burning
a hole in my glaze notebook and I'm ready to try some of the
suggestions.
In a Dec 1986 article (pp. 74-45), "Cone 06 - 6 Vitreous Engobes",
Rowan talks of Bentonite B "a very plastic Texas clay with an
alumina-silica ratio of 1 to 4.5...." I've looked on digitalfire,
googled, and even went to the Milwhite website, but I can't really
find info on Bentonite B. Digitalfire does reference BentoLite B but
there is very little difference between that and generic bentonite
entry.
Rowan writes that "a mixture of 25 parts ball clay and 5 parts
bentonite may be substituted for 30 parts Bentonite B", so I'm really
curious as to how this Bentonite B is different from generic
bentonite.
One further question: Because Rowan's engobes are "dense and vitreous
at cone 06", will that present a problem for me when I bisque green
ware plus the engobes to 04? Will I need to watch out for arrested
burn out at bisque or cooling dunts at 04? I will be trying to wire
that small test kiln I scored awhile back for this project.
Peace out, y'all,
--
Taylor, in Rockport TX
http://wirerabbit.blogspot.com
http://wirerabbitpots.blogspot.com
http://www.flickr.com/photos/wirerabbit/
Donald Burroughs on sat 16 feb 08
We also have naturally occuring Bentonite B here in the Red River and
Pemibina Hills Valley (Southern Manitoba)areas. It was mined for many
years up until 1998 by Pembina Hills Clays Inc. (see this link)
http://www.gov.mb.ca/stem/mrd/busdev/industrial/bentonite.html
and is being reconsidered by Bird River Mines Inc. in a nearby area. Here
in Manitoba we call it "gumbo" because of it's ability to hold water. Also
check out http://en.wikipedia.org/wiki/Bentonite.
It's abundance here can be attributed to an ancient inland shallow sea
known as Agazziz which covered most of Manitoba. Being a calcium based
Bentonite was probably the result of ancient reefs and shellfishes that
would probably occur in a shallow waters. I can also attested to this
montmorillinite have clay like properties and someone here is firing it to
low earthenware temps.. In fact, this so-called gumbo or clay was also
used to manufacture bricks for many an historical buliding in Manitoba up
until about the late 1920's. Quality sources ran out as this "clay" was
plagued with calcium chunks which caused pitting in bricks which were
fired. The last known kiln to (my knowledge)to make brick from that time
frame still exists on private property in southern Manitoba. Known to the
locals as "Leary's",this kiln still has it's last unfired load of brick
according to my sources.
As for it's chemical makeup the word calcium says it all whereas the other
bentonite is primarily sodium based. As for a source, try a local brick
yard as I did. I found six bags (50lb each) of the locally mined bentonite
B and apparently bricklayers used to use this stuff in their mortar mix
for fireplaces. Works great in the Rowan formulae although it is not
bleached of it's RIO content and produces darker colours.
Donald Burroughs
Neon-Cat on tue 19 feb 08
My latest experiment with local North Central Texas Blue Clay was =
interesting. Although the charcoal-gray/dark blue clay body was clean, =
uncontaminated, and free of debris as compared to earlier work with the =
duck-doo marred and junk-filled clay collected at river edge or scraped =
out of run-off streambeds, it can't be pure calcium montmorillonite =
(calcium bentonite, aka Bentonite B). My figurine bisque-fired through =
cone 05 (10460 C or 19140 F) with almost unnoticeable shrinkage. It is =
strong and extremely lightweight. It is a lovely pale-buff/off-white =
color with olive-green flashing - the green looks like an integrated =
terrestrial growth of fine moss or lichen or the beginnings of fuzzy =
aquatic algae. Throughout the body there are plenty of small green =
inclusions, too. The figurine looks so pretty I'm captivated. My marly =
and calcareous clay body, with origins 92-110 million years ago, is no =
doubt full of un-oxidized carbon and calcium carbonate from tiny little =
crab bodies; it probably also contains a dash of iron (2.5% or less), =
and maybe some chlorite or illite (both known to be present in my =
locality). I've got the rolling of ancient worlds along with chemical =
formulas and mechanisms for reaction chemistry dancing through my head. =
Above 9500 C (17420 F) calcium bentonite may begin to form cristobalite, =
mullite, anorthite, and spinel. While at a university it occurred to me =
I might stroll over to the library and learn how to access first-rate =
databases and maybe go make friends over in the geology department. =
Someone somewhere knows exactly what's in this clay body. Then again I =
should be practicing my sculptural technique. If I ever come off my =
present life high a little more personal balance and focus might be =
nice. Meanwhile I'll throw some ground Blue Clay in a bisqued bowl and =
see how it does in our upcoming mid-range glaze firing (cone 6, 12220 C =
or 22320 F) and make up a few more test tiles. Who would have thought =
that riverbank clay could please a gal so much?
Photos (not doing "Buffy" justice, color-wise) are at the end of my =
web-page section "Ceramics in the Works":
http://neon-cat.com/ceramics_in_the_works. =20
In case you're wondering, in-line with thinking about giving titles to =
"work", I give pieces silly-little, easy-to-remember names; "Buffy" is, =
after all, only a tester.
Marian
Neon-Cat Ceramics
neoncat@flash.net=20
www.neon-cat.com=20
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