David Hewitt on tue 24 mar 98
In message , rballou@mnsinc.com writes
>----------------------------Original message----------------------------
snip
>As for B2O3 and expansion, Hamer writes about boracitis. Additions of B2O3
>to a glaze are useful in preventing crazing up to a point, after which any
>more additions have the opposite effect and the glaze crazes. The optimum
>amount of B2O3 differs for each glaze. I don't know if this has any
>relevancy at all to the expansion characteristics of the glaze in question.
>Just add it to the soup pot. Maybe someone else can flesh out this
>observation.
>
I have come across a similar reference in a book by Glenn C Nelson,
'Ceramics- A Potter's Handbook' -p230. It goes as follows:-
"On the whole, however, boric oxide functions as a flux since in
comparison with silica it increases the elasticity, lowers the tensile
strength, and, in limited quantities, lowers the coefficient of thermal
expansion."
By implication this is saying that in more than 'limited quantities' the
coefficient of expansion increases.
More information on this would certainly be welcome as far as I am
concerned.
>It doesn't look like B2O3 will conform to any neat and tidy pigeon holes.
>But isn't that what attracts a lot of us to clay? It won't surprise me a
>bit if testing proves this glaze to be just fine.
I agree, it certainly doesn't conform to any neat and tidy pigeon hole.
>
>Ruth Ballou
>Silver Spring,MD -- where people are starting to feel left out if they
>haven't been called to testify before Ken Starr's grand jury yet.
--
David Hewitt
David Hewitt Pottery ,
7 Fairfield Road, Caerleon, Newport,
South Wales, NP6 1DQ, UK. Tel:- +44 (0) 1633 420647
Own Web site http://www.dhpot.demon.co.uk
IMC Web site http://digitalfire.com/education/people/hewitt.htm
maggie j jones on wed 25 mar 98
I have been following the Boron thread with great interest as I have
been using a glze with boron as a base and keeping away from CaO. for
about 18 yrs. I fire oxidation ,electrically, at ^5-6. The reasons I
stay with Boron are varied but mainly it makes my rutile turn a lemon
yellow as long as the CaO is low. ( my secret has been released, AAAAK!
) Also, I opacify with some tin which will help the lemon yellow. I do
not care for the florescence of praesidonium(sp).
Over the yrs I have fudged with formulas, A lot of boron , it seems,
30% or more say, gives problems in the bucket since it seems to be
partially soluble and application is difficult without crawling. (I also
used to use talc which seemed to have the same tendancy..not with
solubility but made the glaze want to curl up like a mud puddle in early
stages of the fire and fall off the pot. I still would like to test it).
I have since backed off on gerstly borate and replaced some with
boron frits. 3134 seems to be the best 3124 is too refractory, 3195 is
close to 3134 but I have not used it much except along with 3134.
I have recently had a problem , which you may have read ,concerning
"dunting" or so i thought. The problem did not exist until Brian mcArthy
, at highwater clays in Asheville, added pyrophilite to his brownstone
formula to combat a pinholing and blistering problem that ^6ers were
having..not me, and he didn't tell me he made this change in the clay I
'd been using all these yrs....anyway..My pie plates and slab bowls
glazed on one side began breaking within min. after coming out of the
kiln. These are forms We have been producing successfully for yeeeaars! .
After testing,(still going on) I am noticing that the pots are
crazing so bad they break...not dunting. I had been testing with dropping
the silica trying to get away from dunting and the pots still broke but
noticed the crack patterns smaller and closer together. the more silica
the bigger and deeper and fewr the cracks so now i am going the other
direction and waitng on tests with 2-5% increments of More SiO...I have
been hearing from people, Brian for one, " no---, crazing releases the
tension so that the pot does not break". Considering the forms I am
working with , here is an exception.
This is driving me a bit bannanas, because my main interest in playing
with these elements is Simplicity. If this "improvement" that Brian made
on his clay can cause such a problem...I don't care for it...Give me a
clay that has a wide enough range in temp. and expansion that it is
"forgiving"! The old formula works but I have a bunch of biskware to
rescue ...I need a change!
Maggie Jones , Turtle Island Pottery, Black Mtn. NC
mrjj@juno.com
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Richard Burkett on wed 1 apr 98
From David Hewitt (and others) concerning boron in glazes:
>>As for B2O3 and expansion, Hamer writes about boracitis. Additions of B2O3
>>to a glaze are useful in preventing crazing up to a point, after which any
>>more additions have the opposite effect and the glaze crazes. The optimum
>>amount of B2O3 differs for each glaze. I don't know if this has any
>>relevancy at all to the expansion characteristics of the glaze in question.
>>Just add it to the soup pot. Maybe someone else can flesh out this
>>observation.
>>
>I have come across a similar reference in a book by Glenn C Nelson,
>'Ceramics- A Potter's Handbook' -p230. It goes as follows:-
>"On the whole, however, boric oxide functions as a flux since in
>comparison with silica it increases the elasticity, lowers the tensile
>strength, and, in limited quantities, lowers the coefficient of thermal
>expansion."
>By implication this is saying that in more than 'limited quantities' the
>coefficient of expansion increases.
>More information on this would certainly be welcome as far as I am
>concerned.
David,
I did a lot of reading on this while writing HyperGlaze and from what I
could find, what you describe above seems to be the case. I remember one
source (sorry, I don't have the name handy, but as I remember it was one of
the primary investigators of thermal expansion coefficients in the early
part of this century) mentioning that above roughly 15% boron oxide in
glazes the thermal expansion increased. From what I've read the effect of
oxides like boron on the overall thermal expansion seems to depend largely
on how neatly the molecules fit into the glassy matrix, filling holes
between other molecules or not, which would account for some variability
between glazes. It's mostly all available in published form for anyone
wanting to do the research, but you'll have to dig through a lot of
scientific literature.
Richard
Richard Burkett - School of Art, SDSU, San Diego, CA 92182-4805
E-mail: richard.burkett@sdsu.edu <-> Voice mail: (619) 594-6201
Home Page: http://rohan.sdsu.edu/dept/rburkett/www/burkett.html
CeramicsWeb: http://apple.sdsu.edu/ceramicsweb/
HyperGlaze@aol.com & http://members.aol.com/hyperglaze/
_ Richard Burkett, Associate Professor of Art
_ The School of Art Design & Art History, SDSU, San Diego, CA 92182-4805
_ http://www.sdsu.edu/art
_ E-mail: richard.burkett@sdsu.edu - voice mail: (619) 594-6201
_ The CeramicsWeb: http://apple.sdsu.edu/ceramicsweb/
rballou@mnsinc.com on thu 2 apr 98
Richard,
So, does this essentially mean that expansion can't be calculated for
glazes containing more than 15% B2O3? What's the best way to deal with this?
Ruth Ballou
rballou@mnsinc.com
>----------------------------Original message----------------------------
>
>>From David Hewitt (and others) concerning boron in glazes:
>>>As for B2O3 and expansion, Hamer writes about boracitis. Additions of B2O3
>>>to a glaze are useful in preventing crazing up to a point, after which any
>>>more additions have the opposite effect and the glaze crazes. The optimum
>>>amount of B2O3 differs for each glaze. I don't know if this has any
>>>relevancy at all to the expansion characteristics of the glaze in question.
>>>Just add it to the soup pot. Maybe someone else can flesh out this
>>>observation.
>>>
>>I have come across a similar reference in a book by Glenn C Nelson,
>>'Ceramics- A Potter's Handbook' -p230. It goes as follows:-
>>"On the whole, however, boric oxide functions as a flux since in
>>comparison with silica it increases the elasticity, lowers the tensile
>>strength, and, in limited quantities, lowers the coefficient of thermal
>>expansion."
>>By implication this is saying that in more than 'limited quantities' the
>>coefficient of expansion increases.
>>More information on this would certainly be welcome as far as I am
>>concerned.
>
>David,
>I did a lot of reading on this while writing HyperGlaze and from what I
>could find, what you describe above seems to be the case. I remember one
>source (sorry, I don't have the name handy, but as I remember it was one of
>the primary investigators of thermal expansion coefficients in the early
>part of this century) mentioning that above roughly 15% boron oxide in
>glazes the thermal expansion increased. From what I've read the effect of
>oxides like boron on the overall thermal expansion seems to depend largely
>on how neatly the molecules fit into the glassy matrix, filling holes
>between other molecules or not, which would account for some variability
>between glazes. It's mostly all available in published form for anyone
>wanting to do the research, but you'll have to dig through a lot of
>scientific literature.
>
>Richard
>
>
>Richard Burkett - School of Art, SDSU, San Diego, CA 92182-4805
>E-mail: richard.burkett@sdsu.edu <-> Voice mail: (619) 594-6201
>Home Page: http://rohan.sdsu.edu/dept/rburkett/www/burkett.html
>CeramicsWeb: http://apple.sdsu.edu/ceramicsweb/
>HyperGlaze@aol.com & http://members.aol.com/hyperglaze/
>
>_ Richard Burkett, Associate Professor of Art
>_ The School of Art Design & Art History, SDSU, San Diego, CA 92182-4805
>_ http://www.sdsu.edu/art
>_ E-mail: richard.burkett@sdsu.edu - voice mail: (619) 594-6201
>_ The CeramicsWeb: http://apple.sdsu.edu/ceramicsweb/
David Hewitt on sun 5 apr 98
I have come across the following reference in a book, 'Technology of
Enamels' by V.V. Vargin, McLaren 1967.
This relates to the Ceramist Appen and is as follows:-
His coefficients are for use with % Mol not % Wt. x 10-7 /oC
B2O3 = 12.5(4-R)-50
Where 'R' is the ratio of moles of oxides R2O, CaO and BaO to moles of
B2O3.
If the value of 'R' is greater than 4, then the value of B2O3 is taken
as constant at 50.
If alumina is present, 'R' = (R2O + RO - Al2O3) / B2O3
He also has variable coefficents for SiO2, TiO2 and PbO.
Because of the complexity of Appen's coefficents I have never made use
of them. No doubt a computer program could mke this easy and practical
and then we might be able to see if they make any sense.
An interesting project, perhaps, for someone if they would like to take
it up.
David
In message , Richard Burkett writes
>----------------------------Original message----------------------------
>
>From David Hewitt (and others) concerning boron in glazes:
>>>As for B2O3 and expansion, Hamer writes about boracitis. Additions of B2O3
>>>to a glaze are useful in preventing crazing up to a point, after which any
>>>more additions have the opposite effect and the glaze crazes. The optimum
>>>amount of B2O3 differs for each glaze. I don't know if this has any
>>>relevancy at all to the expansion characteristics of the glaze in question.
>>>Just add it to the soup pot. Maybe someone else can flesh out this
>>>observation.
>>>
>>I have come across a similar reference in a book by Glenn C Nelson,
>>'Ceramics- A Potter's Handbook' -p230. It goes as follows:-
>>"On the whole, however, boric oxide functions as a flux since in
>>comparison with silica it increases the elasticity, lowers the tensile
>>strength, and, in limited quantities, lowers the coefficient of thermal
>>expansion."
>>By implication this is saying that in more than 'limited quantities' the
>>coefficient of expansion increases.
>>More information on this would certainly be welcome as far as I am
>>concerned.
>
>David,
>I did a lot of reading on this while writing HyperGlaze and from what I
>could find, what you describe above seems to be the case. I remember one
>source (sorry, I don't have the name handy, but as I remember it was one of
>the primary investigators of thermal expansion coefficients in the early
>part of this century) mentioning that above roughly 15% boron oxide in
>glazes the thermal expansion increased. From what I've read the effect of
>oxides like boron on the overall thermal expansion seems to depend largely
>on how neatly the molecules fit into the glassy matrix, filling holes
>between other molecules or not, which would account for some variability
>between glazes. It's mostly all available in published form for anyone
>wanting to do the research, but you'll have to dig through a lot of
>scientific literature.
>
>Richard
>
>
>Richard Burkett - School of Art, SDSU, San Diego, CA 92182-4805
>E-mail: richard.burkett@sdsu.edu <-> Voice mail: (619) 594-6201
>Home Page: http://rohan.sdsu.edu/dept/rburkett/www/burkett.html
>CeramicsWeb: http://apple.sdsu.edu/ceramicsweb/
>HyperGlaze@aol.com & http://members.aol.com/hyperglaze/
>
>_ Richard Burkett, Associate Professor of Art
>_ The School of Art Design & Art History, SDSU, San Diego, CA 92182-4805
>_ http://www.sdsu.edu/art
>_ E-mail: richard.burkett@sdsu.edu - voice mail: (619) 594-6201
>_ The CeramicsWeb: http://apple.sdsu.edu/ceramicsweb/
>
--
David Hewitt
David Hewitt Pottery ,
7 Fairfield Road, Caerleon, Newport,
South Wales, NP6 1DQ, UK. Tel:- +44 (0) 1633 420647
Own Web site http://www.dhpot.demon.co.uk
IMC Web site http://digitalfire.com/education/people/hewitt.htm
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