Cathy Durham on fri 18 oct 96
Some of the recipes offered here include COLEMANITE and one raku has as much
as 60%. In my limited experience I have only known of colemanite to be a
potential problem. A potter/geologist here says that up to 10% should be OK.
But one friend had a colemanite glaze spit all over the inside of her elec.
kiln (I don't know the % in that glaze). We did a raku firing and the glaze
with colemanite in it (I think 15%?) fell/splattered off the pot during
firing. Hamer
in POTTER'S DICTIONARY says it can encourage crawling. So I tend to
avoid/disregard the recipes with over 10%. Am I missing something... do
these recipes that others say work for them have some other ingredient that
counteracts colemanite problems? Or is the composition of Colemanite that we
get here (New Zealand) possibly different enough to be creating the
problems? Just curious.... Thanks! Cathy
Tom Buck on sat 19 oct 96
Cathy of NZ raises the Colemanite question again. Briefly, Turkish
colemanite doesn't come to USA/Canada as such; we use Gerstley Borate from
California instead. The problem with Colemanite is that it contains
Gyspum, in varying, unknown amounts, and if you have ever by error
included some plaster of paris in your reworked claybody then you are well
aware of what happens when Gyspum is fired. Pits and gouges. Well,
Colemanite behaves the same way but unfortunately some bags have less
gyspum, some more. So today the glaze works, next year, blooey.
The only safe way to avoid this is to switch to a borate frit.
Cheers TomB Hamilton ON Canada URL http://digitalfire.com/magic/tombuck.htm
Harvey Sadow on sat 19 oct 96
Cathy Durham wrote:
>
> ----------------------------Original message----------------------------
> Some of the recipes offered here include COLEMANITE and one raku has as much
> as 60%. In my limited experience I have only known of colemanite to be a
> potential problem. A potter/geologist here says that up to 10% should be OK.
> But one friend had a colemanite glaze spit all over the inside of her elec.
> kiln (I don't know the % in that glaze). We did a raku firing and the glaze
> with colemanite in it (I think 15%?) fell/splattered off the pot during
> firing. Hamer
> in POTTER'S DICTIONARY says it can encourage crawling. So I tend to
> avoid/disregard the recipes with over 10%. Am I missing something... do
> these recipes that others say work for them have some other ingredient that
> counteracts colemanite problems? Or is the composition of Colemanite that we
> get here (New Zealand) possibly different enough to be creating the
> problems? Just curious.... Thanks! Cathy
Cathy,
Replace the colemanite with gerstley borate.
HS
Don Jones on sat 19 oct 96
>----------------------------Original message----------------------------
>Some of the recipes offered here include COLEMANITE and one raku has as much
>as 60%. In my limited experience I have only known of colemanite to be a
>potential problem. A potter/geologist here says that up to 10% should be OK.
>But one friend had a colemanite glaze spit all over the inside of her elec.
>kiln (I don't know the % in that glaze). We did a raku firing and the glaze
>with colemanite in it (I think 15%?) fell/splattered off the pot during
>firing. Hamer
>in POTTER'S DICTIONARY says it can encourage crawling. So I tend to
>avoid/disregard the recipes with over 10%. Am I missing something... do
>these recipes that others say work for them have some other ingredient that
>counteracts colemanite problems? Or is the composition of Colemanite that we
>get here (New Zealand) possibly different enough to be creating the
>problems? Just curious.... Thanks! Cathy
A 60/40 split of colemanite(Gerstly Borate) and neph sy is a WONDERFUL
reliable raku glaze for white crackle.
I'm not sure what your problems were but I've never had a problem. On some
clay bodies it peels of tho.
Don Jones
claysky@highfiber.com
Don Sanami on sun 20 oct 96
Cathy, We have used Colemanite/Gerstley Borate, in amounts up to 80%,in
glazes from cone 04 to cone 9 without any problems except when we may
have found the mix contaminated by other materials. At present at cone 6
to 7 we are using the simple formula: Colemanite 50. Flint 32.5. Kaolin
17.5 as a clear glaze.Possibly,the very low fire of Raku may effect the
materials other than Colemanite in the melt,which effects the
Colemanite.don.On Sat, 19 Oct 1996, Harvey Sadow wrote:
> ----------------------------Original message----------------------------
> Cathy Durham wrote:
> >
> > ----------------------------Original message----------------------------
> > Some of the recipes offered here include COLEMANITE and one raku has as much
> > as 60%. In my limited experience I have only known of colemanite to be a
> > potential problem. A potter/geologist here says that up to 10% should be OK.
> > But one friend had a colemanite glaze spit all over the inside of her elec.
> > kiln (I don't know the % in that glaze). We did a raku firing and the glaze
> > with colemanite in it (I think 15%?) fell/splattered off the pot during
> > firing. Hamer
> > in POTTER'S DICTIONARY says it can encourage crawling. So I tend to
> > avoid/disregard the recipes with over 10%. Am I missing something... do
> > these recipes that others say work for them have some other ingredient that
> > counteracts colemanite problems? Or is the composition of Colemanite that we
> > get here (New Zealand) possibly different enough to be creating the
> > problems? Just curious.... Thanks! Cathy
>
> Cathy,
> Replace the colemanite with gerstley borate.
> HS
>
Evan Dresel on sat 9 nov 96
At 07:59 AM 10-19-96 EDT, you wrote:
>----------------------------Original message----------------------------
>Cathy of NZ raises the Colemanite question again. Briefly, Turkish
>colemanite doesn't come to USA/Canada as such; we use Gerstley Borate from
>California instead. The problem with Colemanite is that it contains
>Gyspum, in varying, unknown amounts, and if you have ever by error
>included some plaster of paris in your reworked claybody then you are well
>aware of what happens when Gyspum is fired. Pits and gouges. Well,
>Colemanite behaves the same way but unfortunately some bags have less
>gyspum, some more. So today the glaze works, next year, blooey.
> The only safe way to avoid this is to switch to a borate frit.
>
>Cheers TomB Hamilton ON Canada URL http://digitalfire.com/magic/tombuck.htm
>
Hmm, I wonder if you could calcine it to get rid of the water in the gypsum?
But maybe the colemanite would melt first...
-- Off the top of Evan's head.
Michael Banks on thu 27 jul 00
Only if you want to go to the trouble of making a frit. Calcining is usually
applied to refractory substances. Heating colemanite and cooling it results
in a soft glass. Crushing and pulverising this results in calcium borate
frit. Commercial calcium borate frits though, are formulated with some
silica and alumina to reduce solubility and rehydration.
Michael
Bruce Gioia wrote: (snip)
----- Original Message -----
> this is all interesting news.
> Would calcining provide any relief
> from these irritating bad habits of colemanite?...
Richard Aerni on thu 28 sep 06
If you google Colemanite, you get, among other hits, a site
http://www.colemanite.com , which indicates that colemenite is back on the
market. I remember using it in glazes in the mid 70s, and then it
disappeared. My mineralogy texts indicate that it is a calcium borate
associated with Hydrogen and Oxygen (chemical water of composition?) which
is a purer form of boron than gerstley borate. It is depositional in
nature, forming crystals and geodic nodules from boron rich water runoff
coming into sedimentary playas (think dry deltas). It is found in the Death
Valley region of California, in Nevada, in western Turkey, and in
Kazakhstan. I don't specifically remember how it acted, better or worse,
but if it's available (there is surprisingly little information at the
website), it might be worthwhile to give it a try.
That's about all I have to say about that (to paraphrase Forest Gump)...
Good luck,
Richard Aerni
Rochester, NY
mel jacobson on sun 10 dec 06
materials for glaze come and go...it is
one of things we can be sure of. it changes all the time.
the `new colemanite` will need a great deal of testing.
i doubt that it is a sure thing...ready to go.
colemanite is an industrial material, used for the paint industry
etc...often it is not melted...it is a filler material, like whiting CC.
it would be far easier to use tried and true materials
that we know work. trying to make colemanite work
for glazes seems to me to be a very `long shot`.
there are thousands of recipes out there...find one
that works and then make some pots.
mel
from: mel/minnetonka.mn.usa
website: http://www.visi.com/~melpots/
Clayart page link: http://www.visi.com/~melpots/clayart.html
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