Lili Krakowski on mon 6 jun 11
This is kinda an offshoot from message to Kelly re: glaze for her =3D
exciting new project.
And this message is esp. for beginners, and those who claim they =3D
"cannot" understand glaze.
Glazes all belong to families. One of the most used at c.6 is the =3D
calcium-borate family, to which Karen's Clear belongs.
55.6 Frit--Ferro 3134
23.8 Kaolin--EPK
20.6 Flint
.303 Na2O
.003 K2O
.002 MgO
.691 CaO
.287 Al2O3
.604 B2O3
3.069 SiO2
10.7 Ratio
72.6 Exp
Calculation by Glaze Master (TM)
Now there are Heaven knows how many calcium borate glazes, and they =3D
share the characteristics/influences of boron, and the relative =3D
"neutrality" of calcium as a flux.
There is totally nothing to fall off your chair about with these glazes. =
=3D
They are sturdy and patient. Any defects that appear--rarely--are =3D
easily corrected--generally by adjusting flint.
Many of these glazes have "offshoots": replacing some of the calcium =3D
with magnesium creates "cousin" glazes that give lovely cream effects, =3D
but also "purple" cobalt. One can add zinc for other effects.
I wish there were not so much anxiety and elitism about glaze. If =3D
Cannonball had thumbs she could mix glazes. If she could read she could =
=3D
figure them out! =3D20
In the higher ranges of firing soda/potash/lithium become the prime =3D
fluxes, and boron as a rule drops out. Again: there always is a basic =3D
underlying family trait..and the glazes are very similar. =3D20
It needs to be added that fuel burning kilns, allowing reduction; and =3D
digitally controlled electric kilns that allow controlled holds and =3D
coolings, have a strong effect on glaze results. This does not alter =3D
the fact that glazes belong to families. Just as people do. You may =3D
have cousins in India , Israel, France, Argentina:--you still are one =3D
genetic family...You may have a calcium borate glaze for c.05 or c.4, =3D
or 6 and it still is part of a family.
So Karen Clear above should give some of you a starting point. I hope.
Lili Krakowski
Be of good courage
David Finkelnburg on tue 7 jun 11
Just to add to what Lili wrote so very, very, very well...
The column of numbers under the recipe tells so much. For example, the
ratio of sodium and potassium (Na2O + K20 =3D 0.306) to calcium and magnesi=
um
(CaO + MgO =3D 0.693) is, as is usual for glossy glazes, about 0.3:0.7. Ger=
man
chemist Hermann Seger figured this out in the late 1800s. That ratio of
fluxes produces the glossiest glazes.
The ratio of silica (SiO2) to alumina (Al2O3) is 3.069:0.287, or in very
rounded numbers, 10:1. Back in 1914 Stull and Howatt published a graph of
silica to alumina ratios that showed the glossiest glazes (which they calle=
d
"bright") were between 7 and 10 to 1.
Note that the flux numbers all add up to 1. They are moles of flux, and
for every mole of flux there are ~3 moles of silica and 0.3 moles of alumin=
a
and 0.6 moles of boron in Karen's Clear. The fact of glass science is, was
and always will be that the ratio of the oxides within the glass determines
whether it flows smoothly onto the clay at a given firing temperature
and whether it remains clear or crystals precipitate out of it.
By following Lili's chemical approach to glazes it is possible to see
that many recipes have similar chemistries and "in general" will work and
appear the same even when made from different ingredients.
Now if I could just get the cat to mix glazes...she
also lacks thumbs...but I fear she also has no interest in the work
involved! :-(
Good glazing,
Dave Finkelnburg
http://www.mattanddavesclays.com
----------------------------------------------------------------------
Date: Mon, 6 Jun 2011 07:05:21 -0400
From: Lili Krakowski
....And this message is esp. for beginners, and those who claim they =3D
"cannot" understand glaze.
Glazes all belong to families. One of the most used at c.6 is the =3D
calcium-borate family, to which Karen's Clear belongs.
55.6 Frit--Ferro 3134
23.8 Kaolin--EPK
20.6 Flint
.303 Na2O
.003 K2O
.002 MgO
.691 CaO
.287 Al2O3
.604 B2O3
3.069 SiO2
10.7 Ratio
72.6 Exp
Calculation by Glaze Master (TM)
Lili Krakowski on tue 7 jun 11
Dave: Cannonball--though she would deny it under oath-- IS a cat (most =3D
of the time.)
So maybe we could have a workshop on Glazes for Cats?
Eric Hansen on tue 7 jun 11
Making an understanding of glaze "simple" may not always seem simple.
For example, wood ash makes a fine cone 10 glaze. Volcanic Ash from
Mount Saint Helens makes a fine cone 10 glaze. Albany Slip makes a
fine cone 10 glaze.
Simple? Yes, but why the material works as it does and does what it
does isn't necessarily simple. Because the materials themselves are
complex.
Unity formula spells out how many molecules of three classes of
chemical compounds, and which compounds (not necessarily the same
expression as materials themselves!) are kept in a fixed ratio.
There are at least two other ways we look at what is in a glaze,
although Unity is perhaps not such a bad way to look at it.
Traditionally ceramic engineers use this approach.
An archeologist might send a glaze sample in for analysis, and what
she/he gets in return is an UPA - ultimate percentage analysis - how
much percentage is silica, alumina, calcium, etc. Although normally we
convert this percentage back into Unity to do calculations - we
actually don't have to, if we only knew the math.
Then there is the much-maligned approach that most potters actually
use. Batch. Recipe. If you are going to mix a glaze from scratch that
is the one thing you really can't do without, so it becomes quite
naturally, the primary departure point, regardless of how industry or
science might look at what we are doing.
The problems with recipe arise because (1) any given material may
change over time due to variations in mining location (2) availabliity
of a material may change (3) "neph sy" in Nigeria may be different
than neph sy in Oregon, or say, Australia. (4) the glaze itself may
change over time after it has been mixed and test (5) on and on ...
Another idea of "simple" is in the way the batch is expressed verbally such=
=3D
as:
"Hambone's 123":
Hambone=3D92s 123 - cone 6
1 silica
2 epk
3 wollastonite
- okay - that is called "batch" and is measured by weight - so - what
is the recipe?
Recipe: Percent
wollastonite 50.00
kaolin 33.33
flint 16.67
Totals: 100 % - rounded off numbers, obviously
one computer-application I use gets me close numbers: Unity and Percentage:
Unity Formula for Hambone's 123:
0.003 K2O 0.316 Al2O3 2.285 SiO2
0.004 Na2O 0.004 Fe2O3 0.004 TiO2
0.945 CaO 0.001 P2O5 0.000 MnO2
0.047 MgO 7.2:1 Si:Al Ratio
Percentage Analysis for Hambone's 123:
Percentage
Analysis
by weight:
60.73 % SiO2
14.26 % Al2O3
0.13 % K2O
0.11 % Na2O
23.45 % CaO
0.84 % MgO
0.28 % Fe2O3
0.06 % P2O5
0.14 % TiO2
Possible Health Hazards:
Flint: free silica-wear a NIOSH approved dust mask when handling dry materi=
=3D
al
Estimated Thermal Expansion =3D3D 6.89x10-6 /deg. C
This glaze is outside the recommended limits for calcium, about half
of that base with the rest in another base is recommended.
The glaze tends to craze but is otherwise useful. To complete the
problem, correct the crazing.
--=3D20
Eric Alan Hansen
Stonehouse Studio Pottery
Alexandria, Virginia
americanpotter.blogspot.com
thesuddenschool.blogspot.com
hansencookbook.blogspot.com
"Simplify, simplify, simplify" - Thoreau
May Luk on tue 7 jun 11
I think one way to speed up the understanding of glazes is to call out
the specifics of a glazes by their characteristics & basic chemical
make up. eg; alkaline glossy transparent, zinc matte, calcium matte,
tin white, rutile iridescent (?). Without looking at the analysis, we
have a good idea of the materials involved. There are about 10 common
oxides that we deal with, not a whole lot to memorize, really. Also,
it's quite simple to make up an aide-m=3DE9moire of which oxide is flux
and what it does, opacifier or colorant and have it be ready when one
look at a recipe to see the function of each material.
I am not against glaze calculations, but one has to do a lot of
firings and really think through and observe the results to give it
meanings. Otherwise, it's just a bunch of abstract numbers. I think
Ron Roy is the only one I know that can read an glaze analysis and
know what it is saying cause he fires so many tiles and he solves a
lot of glaze cases for us and for his job. (Apology if I miss any
other glaze calculation experts. I don't know that many people.)
About glaze learning, if you can't get into it, change the teacher,
but don't do it the fun way, as in taking a joke traffic course for
your driving tickets. it's only fun if you have interest in it and
really want to learn. It is part of the craft, suck it up.
May
Brooklyn NY
--=3D20
http://twitter.com/MayLuk
http://www.ceramicsbrooklyn.com/
Ron Roy on thu 9 jun 11
I think May is saying something important here - and it is interesting.
The best way to understand a glaze analysis is to understand the role =3D20
each oxide plays in a glaze or clay body. For instance - if you =3D20
understand which oxides help the melt - at the cone you are working at =3D2=
0
- then increasing those oxides will help lower the melting temperature =3D2=
0
of the clay or glaze.
Understanding which oxides raise the melting temperature allows you to =3D2=
0
do the same thing.
It is simply not that complicated if you have a basic understanding of =3D2=
0
what the oxides do.
The best way I know to understand the oxides is to look them up on the =3D2=
0
Hamer book.
RR
Quoting May Luk :
> I think one way to speed up the understanding of glazes is to call out
> the specifics of a glazes by their characteristics & basic chemical
> make up. eg; alkaline glossy transparent, zinc matte, calcium matte,
> tin white, rutile iridescent (?). Without looking at the analysis, we
> have a good idea of the materials involved. There are about 10 common
> oxides that we deal with, not a whole lot to memorize, really. Also,
> it's quite simple to make up an aide-m=3DE9moire of which oxide is flux
> and what it does, opacifier or colorant and have it be ready when one
> look at a recipe to see the function of each material.
>
> I am not against glaze calculations, but one has to do a lot of
> firings and really think through and observe the results to give it
> meanings. Otherwise, it's just a bunch of abstract numbers. I think
> Ron Roy is the only one I know that can read an glaze analysis and
> know what it is saying cause he fires so many tiles and he solves a
> lot of glaze cases for us and for his job. (Apology if I miss any
> other glaze calculation experts. I don't know that many people.)
>
> About glaze learning, if you can't get into it, change the teacher,
> but don't do it the fun way, as in taking a joke traffic course for
> your driving tickets. it's only fun if you have interest in it and
> really want to learn. It is part of the craft, suck it up.
>
> May
> Brooklyn NY
> --
> http://twitter.com/MayLuk
> http://www.ceramicsbrooklyn.com/
>
ivor and olive lewis on fri 10 jun 11
Dear Ron Roy,
Reading May Luk's post brought to mind a family of glazes usually given the
appellation of "Lime Felspar". Examples are the Classic "Rhodes 32" and
Leach's "4-3-2-1".
But for an understanding of the properties imparted by various oxides the
best summary is the table given by Frank Hamer, "Table of oxide influence
upon viscosity".
Although your suggestion "if you understand which oxides help the melt - at
the cone you are working at - then increasing those oxides will help lower
the melting temperature of the clay or glaze." may seem both rational and
logical, it is adding a Compound which Contains the Target Oxide that will
achieve this result. Some individual oxides are highly reactive and not
available by the kilo. As an example, Sodium oxide reacts violently with
water and freely with Carbon dioxide. But Sodium Carbonate would achieve
your goal.
Best regards,
Ivor Lewis,
REDHILL,
South Australia
Lili Krakowski on mon 6 feb 12
I was very happy when I saw in a Mel-post mention of glaze as family. =3D
And Paul Lewing's addendum.
But I would--as I have for decades--move on from "Where Did Aunt Mitzi =3D
Get That Awful Dress?" and " Here's Cousin Bill Bottom-Pincher !" and =3D
get to
who has red hair, and which family members are born sans wisdom teeth.
I wish that when we speak of The Family of Glaze we would speak of =3D
calcium borate glazes, slip glazes, Shinos as (apparently) high alumina =3D
alkaline glazes and so on. It would wean neophytes from the =3D
recipe-collection cult to the much more sensible (IMO) =3D
composition-of-glaze thought pattern.
Over and over and over "we" see recipes that are identical--or nearly =3D
so--in formula, but hide that fact by using different materials. As =3D
often said: Colemanite "became" Gerstley Borate, "became" a number of =3D
frits. This Soda Spar disappeared, That One replaced it, and now That =3D
One is being replaced by Yet Another. =3D20
I respectfully suggest that while thinking along these family lines will =
=3D
annoy those who keep their recipes notebooks in a safe, the rest of us =3D
would have an easier time both with our work and with our teaching.
Lili Krakowski
Be of good courage
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