Wayne Kilburn on wed 1 may 02
Hello:
New lurker here, trying my hand at posting for the
first time. I'm returning to clay after a 20 year
hiatus, and I'm trying my hand at mixing and
formulating glazes. I have a question about Loss On
Ignition - what effect does it have on a glaze?
For example, I am attempting to substitute
wollastonite for whiting in Ron Roy's revision of
Xavier's Warm Jade Green base (see below). Simply, I
am trying this because I have wollastonite and I don't
have whiting. I'd rather use ingredients I already
have than buy one more bag, if I can get the same
result. I have not done any real world testing yet,
but I will as time permits. For now, I am interested
in understanding the principles of glaze formulation
and their effects on the final glaze.
Revised Xavier's Warm Jade Green Base (^6 Oxidation)
22 Custer Feldspar
16 FRIT 3124
20 EPK
21 SILICA
9 Talc
12 Whiting
Weight 316.99
Si:Al 7.90
SiB:Al 8.14
Expan 6.42
LOI 8.06
CaO 0.56
MgO 0.26
K2O 0.09
Na2O 0.09
Fe2O3 0.00
Al2O3 0.44
B2O3 0.11
SiO2 3.46
TiO2 0.00
In my revision I have replaced the whiting with
slightly more wollastonite, then added a bit more
Custer and reduced the silica to achieve a similar
Seger formula (see below).
Revised Xavier's Warm Jade Green Base (^6 oxidation)
with Wollastonite
27 custer feldspar
16 FRIT 3124
20 EPK
14 SILICA
14 wollastonite
9 talc
Weight 325.55
Si:Al 7.85
SiB:Al 8.09
Expan 6.50
LOI 2.79
CaO 0.55
MgO 0.25
K2O 0.11
Na2O 0.10
Fe2O3 0.00
Al2O3 0.45
B2O3 0.11
SiO2 3.56
TiO2 0.00
The numbers for fluxes are fairly close. The
differences I noticed were in the LOI (8.06 original,
2.79 with wollastonite), higher weight and silica and
lower Si:Al).
Finally, my question: given these theoretical
differences, what differences would be expected
between the final glazes? Are there any conclusions I
can draw from a glaze's Seger formula - ie, can I
recognize a glaze that may run or craze based on
numeric relationships between the ingredients? I think
understand that the Seger formula is a numeric
expression of the relative amounts of fluxes, glass
formers and stabilizers, but what do I look for to
decide if a glaze is worth testing?
Thanks for any education you can provide.
Wayne Kilburn
Lake Stevens, Washington
__________________________________________________
Do You Yahoo!?
Yahoo! Health - your guide to health and wellness
http://health.yahoo.com
Karen on thu 2 may 02
Wayne,
While I can not begin to respond to the specifics of your questions, as you
are obviously more experienced at this than I am to begin with (but I'm
getting there!) There are plenty of wonderful "Glaze Guru's" who will
respond with some great answers, which will help clarify it for us all!
I would like to mention Ian Currie's books. His more recent one is very
much focused on testing glazes & knowing about how to go about so in an
organized manner in order to understand the results.
you said:
"Finally, my question: given these theoretical
differences, what differences would be expected
between the final glazes? Are there any conclusions I
can draw from a glaze's Seger formula - ie, can I
recognize a glaze that may run or craze based on
numeric relationships between the ingredients? I think
understand that the Seger formula is a numeric
expression of the relative amounts of fluxes, glass
formers and stabilizers, but what do I look for to
decide if a glaze is worth testing?"
With the method Ian uses you can test small amounts & truly understand what
your results are & why. I was truly blessed to have the opportunity to
take Ian's workshop in Wentworth, NC (near Greensboro, NC) and learned a
tremendous amount from his methods.... I have been reading & studying on my
own a lot. I was beginning to think it was just beyond me, all this glaze
formulation, results, how-to's and such. His methods, workshop & wonderful
explanations helped me to get past that stage. I Know Now when I start
testing I will have a starting point and the foundation for testing to
determine if a glaze is worth continued testing. I would not be using much
in the way of ingredients as far as large quantities, thus if a glaze was
not durable, safe or desireable in any way, I will not have lost much & in
actuality would have learned a great deal.
Ian is conducting one more workshop this weekend in Arkansas, then off to
Arizona and back home to Australia until next fall. He will be back
stateside doing workshops at that time & is indeed formulating his plans
even now. If you have the opportunity to do a workshop with him, DO.... in
the meantime his books are Great & easily understood.
As for the more detailed questions you have ( which are still yet beyond
me! ;-) John or Ron, or Vince or Ababi or one of MANY other wonderful
clayarters will gladly respond with accurate & enlightening information!
Good luck in all your ventures..... it sure is fun!
Karen
(near Raleigh, NC, still wishing it would rain..... it rumbled last nite &
did nothing.... that I can tell....ground's not even damp! :)
(ps. do a search in the Archives for Ian Currie & how to purchase his
book(s).... you can purchase it directly from him.....and I am sure there
are other venues as well.)
Paul Lewing on thu 2 may 02
on 5/1/02 10:13 PM, Wayne Kilburn at wbkilburn@YAHOO.COM wrote:
> Finally, my question: given these theoretical
> differences, what differences would be expected
> between the final glazes?
Wayne, if you did your substitution with a good calculation program, it
should have compensated for LOI, so if you have made up identical Seger
formulas, the resulting glazes should be the same, assuming the analyses in
your database for all the materials were accurately reflecting the materials
you used.
Are there any conclusions I
> can draw from a glaze's Seger formula - ie, can I
> recognize a glaze that may run or craze based on
> numeric relationships between the ingredients?
Yes, you can. The number you want to look at for running would be the Si:Al
ratio. Most usable glazes have a ratio between 5 and 12. Below that and
you're likely to get a dry "lichen" type glaze. Above that and it's likely
to run. This is true across all temperatures. Crazing is also pretty easy
to predict with software, at least for glossy glazes. Matte glazes are a
bit more problematical. What you need to do is find a glaze that fits your
clay, made into the size and thickness of pots that you like to make, fired
and cooled on your schedule, in your kiln. Then any other glaze with this
same coefficient of expansion number should also fit your work.
I think
> understand that the Seger formula is a numeric
> expression of the relative amounts of fluxes, glass
> formers and stabilizers, but what do I look for to
> decide if a glaze is worth testing?
This was my big question before I got my first calculation software program
(I now have 4 of them). And I can now pretty well predict whether a new
recipe will melt at my temperature and whether it will fit my clay. You
understand, it still might be butt-ugly, but that's another issue. I know
what I need for a COE number to fit my clay, but here are the things I look
at to see if it will melt:
1. Si:Al ratio.
2. Percent by weight of silica. I find this to be a more accurate predicter
than limit formulas for SiO2. At my temperature (cone 4), I need between 52
and 64% SiO2. Above or below that, and the glaze will be dry. You need
more as you fire higher, and up at cone 10, the range is more like 57-70%.
3. Makeup of the fluxes. Obviously, a flux mole made up of Na2O, K2O and
PbO would melt at a much lower temperature than a mole made up of CaO, MgO
and BaO. I've actually invented a crude viscosity index that weights the
fluxes by power, and I find it to be very useful.
4. The amount of B2O3. This is especially important at low-fire and
mid-range temperatures. A mix of less active fluxes, and even a shortage of
silica can be compensated for with boron. I don't include boron in unity
when I do calculation, but I include it with the fluxes in my viscosity
index.
I find that any glaze that falls within the acceptable parameters for ratio,
%SiO2, and VI# will work for me. If only two of those numbers are within
those parameters, I'll probably test it if it looks interesting. If only
one does, it probably won't work, and if none of them do, I know it won't
work.
Paul Lewing, Seattle
PS. I notice you're from lake Stevens, WA. Stop by the next WA Potters'
Ass. meeting on May 23. I'll be demonstrating calculation programs and
talking about glazes. If you're not a member, contact me privately and I'll
give you directions and times. And drop by the opening of the annual WPA
show at NW Craft Center tomorrow night in Seattle.
David Hewitt on fri 3 may 02
Wayne,
For what it is worth my reconstruction of your glaze using Wollastonite
in place of Whiting comes up with the following recipe
Custer 24.8
Frit 3134 10.1
EPK 24.5
silica 15.7
Talc 9.8
Wollastonite 15.0
This is using my Glaze Workbook and gives a very close replication on
the data I have on these materials. I would expect you to get a very
similar result.
Expansion 4.01 x 10-6/oC Linear English & Turner. This is fairly low
David
In message , Wayne Kilburn writes
>Hello:
>
>New lurker here, trying my hand at posting for the
>first time. I'm returning to clay after a 20 year
>hiatus, and I'm trying my hand at mixing and
>formulating glazes. I have a question about Loss On
>Ignition - what effect does it have on a glaze?
>
>For example, I am attempting to substitute
>wollastonite for whiting in Ron Roy's revision of
>Xavier's Warm Jade Green base (see below). Simply, I
>am trying this because I have wollastonite and I don't
>have whiting. I'd rather use ingredients I already
>have than buy one more bag, if I can get the same
>result. I have not done any real world testing yet,
>but I will as time permits. For now, I am interested
>in understanding the principles of glaze formulation
>and their effects on the final glaze.
>
>Revised Xavier's Warm Jade Green Base (^6 Oxidation)
>
>22 Custer Feldspar
>16 FRIT 3124
>20 EPK
>21 SILICA
>9 Talc
>12 Whiting
>
>Weight 316.99
>Si:Al 7.90
>SiB:Al 8.14
>Expan 6.42
>LOI 8.06
>
>CaO 0.56
>MgO 0.26
>K2O 0.09
>Na2O 0.09
>Fe2O3 0.00
>
>Al2O3 0.44
>B2O3 0.11
>
>SiO2 3.46
>TiO2 0.00
>
>In my revision I have replaced the whiting with
>slightly more wollastonite, then added a bit more
>Custer and reduced the silica to achieve a similar
>Seger formula (see below).
>
>
>Revised Xavier's Warm Jade Green Base (^6 oxidation)
>with Wollastonite
>
>27 custer feldspar
>16 FRIT 3124
>20 EPK
>14 SILICA
>14 wollastonite
>9 talc
>
>Weight 325.55
>Si:Al 7.85
>SiB:Al 8.09
>Expan 6.50
>LOI 2.79
>
>CaO 0.55
>MgO 0.25
>K2O 0.11
>Na2O 0.10
>Fe2O3 0.00
>
>Al2O3 0.45
>B2O3 0.11
>
>SiO2 3.56
>TiO2 0.00
>
>The numbers for fluxes are fairly close. The
>differences I noticed were in the LOI (8.06 original,
>2.79 with wollastonite), higher weight and silica and
>lower Si:Al).
>
>Finally, my question: given these theoretical
>differences, what differences would be expected
>between the final glazes? Are there any conclusions I
>can draw from a glaze's Seger formula - ie, can I
>recognize a glaze that may run or craze based on
>numeric relationships between the ingredients? I think
>understand that the Seger formula is a numeric
>expression of the relative amounts of fluxes, glass
>formers and stabilizers, but what do I look for to
>decide if a glaze is worth testing?
>
>Thanks for any education you can provide.
>
>Wayne Kilburn
>Lake Stevens, Washington
>
>
>__________________________________________________
>Do You Yahoo!?
>Yahoo! Health - your guide to health and wellness
>http://health.yahoo.com
--
David Hewitt
David Hewitt Pottery ,
7 Fairfield Road, Caerleon, Newport,
South Wales, NP18 3DQ, UK. Tel:- +44 (0) 1633 420647
FAX:- +44 (0) 870 1617274
Web site http://www.dhpot.demon.co.uk
Ron Roy on tue 7 may 02
Hi Wayne,
I calculated your (or should I say our) glaze with wolastonite - and I got
very close - more on this later.
Yes you did get the fluxes close - well sort of CaO is down, MgO is up and
so is KNaO - boron is right on - this is a puzzelment - the alumina is up
and so is the silica.
How can this happen - we are both using calculation software?
What is happening - why we are getting different results - has to do with
material analysis we have in our programs. The more accurate those analysis
are the better our chances.
The answer to your questions lie in how accurate the numbers are - so get
good analysis for your materials - especially those that are mined locally.
Wolastonite can vary - so can dolomite - well they all vary but some are
much more likely to vary than others.
Even so - calculation is the best way to work on glazes - no question about
that - the better your materials definition the better it will work.
By the way - the materials definitions in Mastering cone 6 glazes are the
ones I use.
Here is my revision with Wolastonite - send the results of all the
revisions you get to the list and we will all learn a bit more.
CUSTER SPAR......... 22.50 22.50%
F3124............... 17.00 17.00%
EPK................. 20.50 20.50%
SILICA.............. 14.50 14.50%
TALC................ 8.50 8.50%
Wollastonite........ 17.00 17.00%
----------
100.00
FORMULA & ANALYSIS
------------------
*CaO........ .59 10.78%
MnO2....... .00 .01%
*MgO........ .23 2.94%
*K2O........ .08 2.57%
*Na2O....... .10 1.91%
Fe2O3...... .01 .27%
TIO2....... .00 .06%
B2O3....... .11 2.42%
AL2O3...... .43 14.12%
SiO2....... 3.35 64.88%
P2O5....... .00 .03%
RATIO 7.81 (original is 7.80)
EXPAN 408.70 (original is 408.38)
WEIGHT 309.38 (original is 309.41)
Now that is close!
All this goes to hell of course if your brand of Wolastonite is different
than mine - and OM#4 does vary some what and there are different kinds of
Talc - NEVER the less - it's still the best tool we have for glaze work -
and you can solve glaze problems with it if you know the function of the
oxides in glaze - that you have to know.
Let me know if you have questions - I have some passion on the subject - as
you have probably discerned.
RR
>Finally, my question: given these theoretical
>differences, what differences would be expected
>between the final glazes? Are there any conclusions I
>can draw from a glaze's Seger formula - ie, can I
>recognize a glaze that may run or craze based on
>numeric relationships between the ingredients? I think
>understand that the Seger formula is a numeric
>expression of the relative amounts of fluxes, glass
>formers and stabilizers, but what do I look for to
>decide if a glaze is worth testing?
>
>Thanks for any education you can provide.
>Wayne Kilburn
Ron Roy
RR #4
15084 Little Lake Road
Brighton
Ontario
Canada - K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
| |
|
