Linda Arbuckle on fri 17 jan 97
I'm not a chemist, nor do I play one on t.v.
BUT, my understanding is that boron (from Gerstley Borate in the Floating
Red recipe, which contains boron. calcium, silica and some sodium) increases
glaze viscosity as well as functions as a flux. In some cases it's cited as
a glass-former as well. At lowfire temps this is a viscosity agent in the
melted glaze. The glaze then doesn't run, but excess boron may cause
crawling. GB boils when it melts, then smooths out (watch raku glazes hi in
gerstley thru the peep some time). This action can promote mottled color,
or just be a pain and cause glaze flaws.
Date: Wed, 15 Jan 1997 09:35:24 EST
From: Bill Amsterlaw
Subject: Subject: Re: Floating Red Glaze for ^6 ox
----------------------------Original message----------------------------
re: viscosity agent
Hi Linda Arbuckle:
Could you please explain what a "viscosity agent" is? Does boron increase the
viscosity or decrease the viscosity of the glaze? Are you talking about
viscosity of raw glaze or viscosity of melted glaze?
On 13 Jan 1997 Linda Arbuckle wrote:
>> Boron (B2O3) functions as both a flux and a viscosity agent <<
- Bill Amsterlaw (wamster@msn.com)
Plattsburgh, NY
Linda Arbuckle
Associate Professor, Graduate Coordinator
University of Florida, Box 115801, Gainesville, FL 32611-5801
e-mail: Linda Arbuckle@ufl.edu
Shelley S. on sat 18 jan 97
Linda,
Broadening this discussion a bit, I understand from some glaze books that
adding small amounts of boron will lower the thermal expansion of a high
fire glaze thus reducing crazing. I've tried adding 1% frit 3134 to a
glaze that crazes but it seems to have only a minimal effect. The glaze
software mentions that the boron causes abnormal expansion, and in some
cases adding the frit increases the expansion data slightly rather than
lowering it. Do you (or others) know anything about this?
Thanks in advance.
Shelley
----------
From: Linda Arbuckle[SMTP:arbuck@nervm.nerdc.ufl.edu]
Sent: Friday, January 17, 1997 7:47 AM
To: Multiple recipients of list CLAYART
Subject: viscosity agent
----------------------------Original message----------------------------
I'm not a chemist, nor do I play one on t.v.
BUT, my understanding is that boron (from Gerstley Borate in the Floating
Red recipe, which contains boron. calcium, silica and some sodium)
increases
glaze viscosity as well as functions as a flux. In some cases it's cited as
a glass-former as well. At lowfire temps this is a viscosity agent in the
melted glaze. The glaze then doesn't run, but excess boron may cause
crawling. GB boils when it melts, then smooths out (watch raku glazes hi in
gerstley thru the peep some time). This action can promote mottled color,
or just be a pain and cause glaze flaws.
Bill Amsterlaw on sat 18 jan 97
Hi Clayart:
Recent posts have varying views on the effects of boron on glaze viscosity and
I am unsure whether these comments refer to raw glaze or the glaze melt and
whether these effects vary at different firing temperatures.
From personal observation, Gerstley Borate seems to gel up a raw glaze - ie,
increase the viscosity of the raw glaze - but from what I read in Rhodes, it
seems likely that borate would lower the viscosity of the glaze melt.
Rhodes states that "Boric oxide is a low-melting-point substance with strong
fluxing power comparable to lead oxide or sodium oxide....It can be used as
the main flux ... and can be used from the lowest to the highest temperatures.
It forms borates that reduce the expansion of the glaze, and so is useful in
the correction of crazing."
Can someone answer with certainty:
1. What effects do boron compounds have on the physical properties of raw
glaze?
2. What effects do boron compounds have on the viscosity of the glaze melt?
Is this effect the same at low and high firing temperatures?
3. What is a really good reference to look such things up?
On 16 Jan 1997 Ron Roy wrote:
>>B2O3 is a runner - lowers viscosity - it is closely grouped with sodium,
potassium and lithium. <<
On 17 Jan 1997 Linda Arbuckle wrote:
>> ...My understanding is that boron (from Gerstley Borate...) increases
glaze viscosity as well as functions as a flux. In some cases it's cited as
a glass-former as well. At lowfire temps this is a viscosity agent in the
melted glaze. The glaze then doesn't run, but excess boron may cause
crawling. GB boils when it melts, then smooths out (watch raku glazes hi in
gerstley thru the peep some time). This action can promote mottled color,
or just be a pain and cause glaze flaws.
- Bill Amsterlaw (wamster@msn.com)
Plattsburgh, NY
Ron Roy on sun 19 jan 97
Shelly said....
>Broadening this discussion a bit, I understand from some glaze books that
>adding small amounts of boron will lower the thermal expansion of a high
>fire glaze thus reducing crazing. I've tried adding 1% frit 3134 to a
>glaze that crazes but it seems to have only a minimal effect. The glaze
>software mentions that the boron causes abnormal expansion, and in some
>cases adding the frit increases the expansion data slightly rather than
>lowering it. Do you (or others) know anything about this?
B2O3 has a very low expasion rate - if there is over 12% in a glaze however
that expansion starts to increase.
Frit 3134 probably has a higher expansion than your glaze and the following
analysis may show you why.
SiO2 46.5
Na2O 10.3
CaO 20.1
B2O3 23.1
As you can see there is enough sodium to off set any advantages nevermind
the calcium. You must realize when you add any material to a glaze you will
affect that glaze and you will have to make adjustments. In this case the
lack of alumina in the frit will create a "need" for it to be replaced in
the glaze. Also note you are adding more flux (sodium, calcium and to some
extent the boron are all melters so you have to top off the alumina and
silics to get the expansion to lower. The best way to do this is with glaze
calculation software.
Ron Roy
Toronto, Canada
Evenings, call 416 439 2621
Fax, 416 438 7849
Ron Roy on sun 19 jan 97
Bill asked...
>
>Recent posts have varying views on the effects of boron on glaze viscosity and
>I am unsure whether these comments refer to raw glaze or the glaze melt and
>whether these effects vary at different firing temperatures.
>
>>From personal observation, Gerstley Borate seems to gel up a raw glaze - ie,
>increase the viscosity of the raw glaze - but from what I read in Rhodes, it
>seems likely that borate would lower the viscosity of the glaze melt.
>
>Rhodes states that "Boric oxide is a low-melting-point substance with strong
>fluxing power comparable to lead oxide or sodium oxide....It can be used as
>the main flux ... and can be used from the lowest to the highest temperatures.
> It forms borates that reduce the expansion of the glaze, and so is useful in
>the correction of crazing."
>2. What effects do boron compounds have on the viscosity of the glaze melt?
>Is this effect the same at low and high firing temperatures?
>
>3. What is a really good reference to look such things up?
Hi Bill my comments were on glaze melt - should have made that clear. Here
are some results of my research.
Taylor and Bull say in Ceramic Glaze Technology "Hi boron glazes mature
rapidly as they are extremely fluid at gloss temperatures, ..." They also
state it lowers surface tension which adds to the fluidity.
See also Hamer's dictionary under viscosity - there is a table of oxide
influence upon viscosity. In the appendix see table #25 on oxide effect on
surface tension. Both tables tables indicate this oxide will move a glaze
if given a chance.
Parmalee says boron is helpful in the formation of glazes that are viscous
at lower temperatures but which are disproportionately more fluid at the
higher temps.
The Hamer book is the most complete text I own and I recommend it. If I had
to start my library over again it would be the first book I would buy.
Ron Roy
Toronto, Canada
Evenings, call 416 439 2621
Fax, 416 438 7849
PJLewing@aol.com on mon 20 jan 97
It's not surprising that gerstley borate would act to increase the viscosity
of your raw glaze. GB is about 43% ulexite ( a calcium borate mineral) and
about 19% bentonite. The rest is mostly water and some other trace minerals.
And we all know what bentonite does when you add water to it. It turns to
slime. It's named for Ft. Benton, Montana, and out there they refer to the
stuff as gumbo mud.
Paul Lewing, Seattle
http://digitalfire.com/magic/lewing. htm
Bob Kavanagh on mon 20 jan 97
Shelley
If you want to use a boron frit (ferro) for this purpose, 3124 has a lower
coefficient than 3134. Get an analysis of these frits from your supplier
and look them over for a better understanding.
bob kavanagh
Bill Amsterlaw on wed 22 jan 97
Hi Paul:
Wow! Gerstley borate is 19% bentonite! That explains the effect that Gerstley
borate has on raw glaze - increasing its viscosity.
I now have most of my original questions answered:
1. Gerstley borate (which is 19% bentonite) increases the viscosity of raw
glaze.
2. Boron decreases the viscosity of the glaze melt.
3. Hamer's would be a good reference to have in my library.
Still unanswered: Does boron or borax per se have any effect on the viscosity
of raw glaze?
- Bill Amsterlaw (wamster@msn.com)
Plattsburgh, NY
==
On 13 Jan 1997 Linda Arbuckle wrote:
>> Boron (B2O3) functions as both a flux and a viscosity agent <<
==
On 17 Jan 1997 Linda Arbuckle explained:
>>
....My understanding is that boron (from Gerstley Borate...) increases glaze
viscosity as well as functions as a flux. In some cases it's cited as a
glass-former as well. At lowfire temps this is a viscosity agent in the melted
glaze. The glaze then doesn't run, but excess boron may cause crawling. GB
boils when it melts, then smooths out (watch raku glazes hi in gerstley thru
the peep some time). This action can promote mottled color, or just be a pain
and cause glaze flaws.
==
On 18 Jan 1997 Bill Amsterlaw wrote:
>>
Recent posts have varying views on the effects of boron on glaze viscosity and
I am unsure whether these comments refer to raw glaze or the glaze melt and
whether these effects vary at different firing temperatures.
<<
==
On 19 Jan 1997 Ron Roy wrote:
>>
My comments were on glaze melt - should have made that clear. Here are some
results of my research.
Taylor and Bull say in Ceramic Glaze Technology "Hi boron glazes mature
rapidly as they are extremely fluid at gloss temperatures, ..." They also
state it lowers surface tension which adds to the fluidity.
See also Hamer's dictionary under viscosity - there is a table of oxide
influence upon viscosity. In the appendix see table #25 on oxide effect on
surface tension. Both tables tables indicate this oxide will move a glaze if
given a chance.
....
The Hamer book is the most complete text I own and I recommend it. If I had to
start my library over again it would be the first book I would buy.
<<
==
On 20 Jan 1997 Paul Lewing wrote:
>>
It's not surprising that gerstley borate would act to increase the viscosity
of your raw glaze. GB is about 43% ulexite ( a calcium borate mineral) and
about 19% bentonite. The rest is mostly water and some other trace minerals.
And we all know what bentonite does when you add water to it. It turns to
slime.
<<
PJLewing@aol.com on thu 23 jan 97
Several days ago I posted a reply to this thread about viscosity with an
observation that it was no wonder Gerstley Borate made your glazes gel, as it
was composed of about 19% bentonite, about 42% ulexite, and the rest mostly
water.
Since then I've been told this is not the case, that that's not what GB
really is. I sent that in because I had just by chance been reading the
section on GB that very day in Mimi Obstler's book, "Out of the Earth Into
the Fire", p.152. She lists as her source a memorandum from the US Borax
Research Corp. from 1989
Perhaps there's someone out there who knows better than I what GB really is
(and better than Ms. Obstler?) and will post it to the list.
Sorry. It really was a neat explanation, though, wasn't it?
Paul Lewing, Seattle
Tony Hansen on fri 24 jan 97
Here's part of what I've got on Gerstley Borate (from FORESIGHT database):
Gerstley Borate is mined by US Borax & Chemical Corp and ground by Hammill
& Gillespie to .3% plus 70 mesh, 2.4% plus 100 mesh, 10.8% plus 140 mesh
and 41.4% plus 200 mesh. The material is used as a constituent in raw
glazes and ceramic bodies, as a bonding agent in grinding wheels and as a
fire retardant.
H&G claim they cannot guarantee quality from lot to lot as the material is
strictly run of the mine and variations can and do occur. The ore does
contain the minerals Colemanite (Ca2B6O11 : 5H2O) and Ulexite (NaCaB5)9 :
8H2O). The sodium and calcium borates found in Gerstley Borate are very
slowly soluble in water.
Tom Buck has researched a bit of history on this
material to determine the nature of the "variations that can and have
occurred" over the past decade. His letter to us said in part:
"The colemanite content can be guesstimated at 30-34%, ulexite content
26-30%, shale (low-iron clay/feldspar/quartz) 20%, limestone 20%. These
proportions would yield a chemical analysis close to H&G's, ignoring of
course, the unknown quantities of other tramp minerals in the ore. One
could therefore consider that today's gerstley borate is only two-thirds
the equivalent of the once common and familiar colemanite, that is, to get
as much boric oxide in a glaze recipe calling for "x" units of colemanite
one needs to use 1.5x (and adjust the clay and whiting content downward in
some recipes)"
NEW FORMULA/ANALYSIS FROM TOM BUCK
----------------------------------
SiO2.............. 9.80 9.80%
Al2O3............. 1.30 1.30%
Na2O.............. 4.70 4.70%
K2O............... .14 .14%
CaO............... 17.90 17.90%
MgO............... 3.50 3.50%
Fe2O3............. .35 .35%
B2O3.............. 28.30 28.30%
*H20 & CO2 IGN LOSS 29.10 29.10%
*ASSUMED INERTS.... 4.91 4.91%
--
=================================================================
Tony Hansen, IMC - Publishers of INSIGHT/FORESIGHT/Magic of Fire
Get INSIGHT 5 beta at http://digitalfire.com/insight5.htm
Ron Roy on fri 24 jan 97
>----------------------------Original message----------------------------
>Several days ago I posted a reply to this thread about viscosity with an
>observation that it was no wonder Gerstley Borate made your glazes gel, as it
>was composed of about 19% bentonite, about 42% ulexite, and the rest mostly
>water.
>Since then I've been told this is not the case, that that's not what GB
>really is. I sent that in because I had just by chance been reading the
>section on GB that very day in Mimi Obstler's book, "Out of the Earth Into
>the Fire", p.152. She lists as her source a memorandum from the US Borax
>Research Corp. from 1989
>Perhaps there's someone out there who knows better than I what GB really is
>(and better than Ms. Obstler?) and will post it to the list.
>Sorry. It really was a neat explanation, though, wasn't it?
>Paul Lewing, Seattle
This is how GB is described in "Ceramic Raw Materials" by D. J. De Renzo.
GB is an ore which contains a mixture of the minerals Colemanite
(Ca2B6O11.5H20) and Ulexite (NaCaB2O9.8H2)). In addition to these minerals
this ore also conains some associated shale.
The calcium borate and sodium calcium borates found in GB are very slowly
soluable in water.
Typical analysis-
B2O3 - 28.0
Na2O - 5.3
CaO - 20.6
Water of crystallization - 25.0 (LOI)
Free water - 0.3 (LOI)
These next 6 are from the shale
SiO2 - 9.5
MgO - 3.5
Al2O3 - 1.1
Fe2O3 - 0.3
CO2 - 3.2 (LOI)
Undetermined - 0.4
Ron Roy
Toronto, Canada
Evenings, call 416 439 2621
Fax, 416 438 7849
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