Randy McCall on sat 6 may 06
I know there are wide firing glazes out there as I have a couple of books
with some formulas, but is there a way to take a glaze that has a narrow
range of firing and turn it into a wide firing glaze or one that will mature
over a greater range of temperatures?
Randy
South Carolina
Pottery Web site
http://members.tripod.com/~McCallJ/index.html
Hank Murrow on sat 6 may 06
On May 6, 2006, at 4:35 AM, Randy McCall wrote:
> I know there are wide firing glazes out there as I have a couple of
> books
> with some formulas, but is there a way to take a glaze that has a
> narrow
> range of firing and turn it into a wide firing glaze or one that will
> mature
> over a greater range of temperatures?
Dear randy;
the more different materials in a glaze, the broader the firing range.
This is because each material brings a different eutectic into play and
at varying temperatures. even trivial(1-3%) amounts can have an efect
on the firing range. My favorite copper blue has 15 ingredients, for
example, and fires from Cone 8 to cone 11.
Now wild materials gathered from nature, are less refined and therefore
more compklex, and generate wider firing ranges naturally. We sorty of
try to synthesize those wild materials when we make a glaze with 15
ingredients.
Cheers, Hank
www.murrow.biz/hank
Ron Roy on sun 7 may 06
Hi Randy,
Not sure I have enough experience to help but - if you are looking for a
glaze that looks the same over 3 or 4 cones - I don't think there is such a
thing.
Unstable (unbalanced) glazes tend to melt very fast - like those with a lot
of flux and not much silica or alumina.
I'm tempted to guess - the more balanced glazes are probably more stable
over different firing temps - check out some limit formulas for clues.
There are some fluxes that have a strong effect like KNaO and Li20 so they
would tend to work against a longer firing range - as would boron. MgO is
special in that it stars to flux around cone 3 to 4 and is quite active
till around cone 7 - so maybe not the best flux to use on a cone 6 glaze
that you want to have a long range.
The alkaline earths like CaO and SrO would then be possibly the best
candidates along with zinc oxide - maybe BaO if you were not concerned
about the toxicity.
So look for glazes which have less of the high fluxing oxides and have more
of the less active - is how I would start.
There are two high calcium mattes in our book - it would be interesting to
see just how they fit into this theory. Perhaps John will have some
comments that will help.
RR
>I know there are wide firing glazes out there as I have a couple of books
>with some formulas, but is there a way to take a glaze that has a narrow
>range of firing and turn it into a wide firing glaze or one that will mature
>over a greater range of temperatures?
>
>Randy
>South Carolina
>Pottery Web site
>
>http://members.tripod.com/~McCallJ/index.html
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Brian Fistler on sun 7 may 06
On Sat, 2006-05-06 at 07:35 -0400, Randy McCall wrote:
> I know there are wide firing glazes out there as I have a couple of books
> with some formulas, but is there a way to take a glaze that has a narrow
> range of firing and turn it into a wide firing glaze or one that will mature
> over a greater range of temperatures?
>
> Randy
> South Carolina
> Pottery Web site
>
Randy,
What do you define as "wide firing range"?
In my (limited) experience with several different brands and types of
commercial glazes that claim to be wide(er)-range firing, I've found
that either the glaze tends to took somewhat underfired at the lower
end, and quite runny at the higher temperatures, not to mention the
colors (especially in the red/yellow/purple range) vary quite a lot
between firing temps.
I'm guessing the manufacturers of most of these glazes are formulated
for a little below the middle temperature range and banking on the users
brushing the glazes onto the ware, creating a somewhat thinner
application (as compared to dipping) so that running at the higher
temperatures and expecting the user to accept a somewhat matt glaze (or
covering the work with a clear glaze of appropriate temperature) at the
lower-end.
Either way, if you are firing to the higher-end temperatures, the glaze
would likely not be as hard/durable as a glaze that was actually
formulated for that higher temperature, as the manufactures are going to
have to reduce the amount of silica and increase the fluxes to get the
glaze to melt acceptably at the lower end of the glaze's rated range.
Brian
Randy McCall on sun 7 may 06
Brian
I am just looking for glazes that are not so sensitive to firing to an exact
temperature (cone 6) without a lot of pinholing. I would also like to know
if there is a material that could be added to a recipe that would help
induce that type behavior. (I have found one comment on ClayArt that may
help with that according to that potter that I want to try) At least within
a cone of Cone 6 up or down. I am getting better at watching cones an
getting a timing of heat work that seems to be working but I would like
glazes that are going to at least mature when the Cone 6 starts bending so
that if for some reason I don't get it quite right I am not having to refire
pots or throw them out.
RR gave me some suggestions with a specific glaze I am going to try and will
apply that to some other glazes to see how it works. It seems that many of
the cone 6 recipes that I try need to need to be fired to cone 7 even though
I am getting a cone 6 touching the shelf. May be the materials I am
using??? Many of the cone 5 glaze formulas seem to work well with my firing
schedule. I would rather change the glaze than my firing schedule as some
glazes work very well with it and so does the clay.
Ivor and Olive Lewis on sun 7 may 06
Dear Randy McCall=20
An interesting proposition ! <<....is there a way to take a glaze that =
has a narrow
range of firing and turn it into a wide firing glaze or one that will =
mature
over a greater range of temperatures?....>>
What have your test results revealed from the recipes you have in your =
possession?
I would say that if you wish to maintain precisely the same qualities of =
surface texture, reflectivity, colour, optical properties such as =
transparency or opacity and so forth the answer will be a resounding =
..."NO"...=20
Several factors are outside your control, a major one being interaction =
at the clay / glaze interface. As temperature rises more and more of the =
body clay will dissolve into the glaze and change its characteristics. =
Then there are the effects of temperature on Viscosity and Surface =
Tension. As temperature increases viscosity will diminish and the melt =
will start to run freely. Don't forget that the rates of dissolution of =
some ingredients changes as temperature rises. Increasing their =
concentration in a melt can lead to chemical reactions and unanticipated =
recrystallisation during cooling, especially if heat loss is retarded.
But if you wish to go ahead and make this a pet project I'm sure you =
will learn a great deal about ceramic science and technology.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Donna Kat on mon 8 may 06
Doesn't Pinnell's Weathered Bronzed Green (and variations) have a wide
range? I know it is used from ^5.5 to ^9. At cone 6 it is a lovely satin
and not the matt from an underfired glossy glaze. I am curious if you see a
problem with it.
Pinnell's
Nepheline Syenite 4920
Strontium Carbonate 1990
Ball Clay-Old Mine #4 1790
Flint 800
Lithium Carbonate 500
Titanium Dioxide 130
Copper Carbonate 670
(Periwinkle uses cobalt but I don't know off hand the amount).
On Sun, 7 May 2006 13:36:29 -0500, Ron Roy wrote:
>Hi Randy,
>
>Not sure I have enough experience to help but - if you are looking for a
>glaze that looks the same over 3 or 4 cones - I don't think there is such a
>thing.
>
>Unstable (unbalanced) glazes tend to melt very fast - like those with a lot
>of flux and not much silica or alumina.
>
>I'm tempted to guess - the more balanced glazes are probably more stable
>over different firing temps - check out some limit formulas for clues.
>
>There are some fluxes that have a strong effect like KNaO and Li20 so they
>would tend to work against a longer firing range - as would boron. MgO is
>special in that it stars to flux around cone 3 to 4 and is quite active
>till around cone 7 - so maybe not the best flux to use on a cone 6 glaze
>that you want to have a long range.
>
>The alkaline earths like CaO and SrO would then be possibly the best
>candidates along with zinc oxide - maybe BaO if you were not concerned
>about the toxicity.
>
>So look for glazes which have less of the high fluxing oxides and have more
>of the less active - is how I would start.
>
>There are two high calcium mattes in our book - it would be interesting to
>see just how they fit into this theory. Perhaps John will have some
>comments that will help.
>
>RR
>
>
>
>
>
>>I know there are wide firing glazes out there as I have a couple of books
>>with some formulas, but is there a way to take a glaze that has a narrow
>>range of firing and turn it into a wide firing glaze or one that will mature
>>over a greater range of temperatures?
>>
>>Randy
>>South Carolina
>>Pottery Web site
>>
>>http://members.tripod.com/~McCallJ/index.html
>
>
>Ron Roy
>RR#4
>15084 Little Lake Road
>Brighton, Ontario
>Canada
>K0K 1H0
>
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>
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>
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Ivor and Olive Lewis on mon 8 may 06
Dear Hank Murrow,
Which definition do you use to explain the term "Eutectic"
<This is because each material brings a different eutectic into play and =
at varying temperatures.>>
Just being inquisitive!
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Daniel Semler on wed 10 may 06
Hi Randy, All,
I have just completed reading Understanding Glazes by Richard Eppler and Mimi
Obstler and in second to last chapter they present a number of glazes showing
how one would make up a batch from a formula. The explain the reasons for
choosing various materials and give the batch recipe. Anyhow, they have
a glaze
that they say is for cone 6 through 9 (or perhaps 10). They note that
it is very
close to the limits of alkali content for cone 6 and thus it will fit
relatively
few bodies in that range, more often than not crazing. This is an interesting
point. Whether this glaze truly looks the same at cone 10 and cone 6 is
another
question. It would be an interesting thing to test a bit.
Of course there are many propeties of a glaze and some may vary considerably
even if the look does not.
Thanx
D
Randy McCall on wed 10 may 06
Dan,,,,,,,,,
Back in the 70's and 80's I used a Glaze base that was Gerstley Borate,
Silicia, and Kaolin. It always fired smooth with no pinholes between Cone 5
and Cone 6. At the time I really never seemed to have any problems with it.
Some of the pieces I am still using after 25 years with no sign of wear.
Some pieces have been in the dishwasher thousands of times. It did have its
limits though on opacity and colors at least with my limited knowledge of
making glazes. I am still able to obtain GB, but was looking maybe for
another good over all wide firing base. Chappell has some reciptes, but
many contain zinc which I have been reluctant to use, but may try some
unless I can find another.
The reason I liked the GB base so much was its brushability and its
characteristic to cover the brush marks so smoothly with an even coat.
Randy
South Carolina
Pottery Web site
http://members.tripod.com/~McCallJ/index.html
May Luk on wed 10 may 06
Hello Randy and friends;
Look into Boron Frits and recipes that contains them
(3195 / 3124 / 3134) I read it on page 195 of 'Out of
the Earth, Into the Fire' by Mimi Obstler, about boron
frits :-
[...] tremendous melting power, stablility, and long
firing range of these boric oxide frits. [...]
Also read about boron oxide in the Hamers dictionary.
Sorry, no quick ideas. Just more reading. :-) I did it
last night, it is good to review this oxide for cone
6.
From my limited experience, zinc is bad news with
Chrome. It turned into an ugly colour! If you don't
want the crystals, fast cool.
Regards
May
P.S. Just a thought. If you layer up earthenware glaze
thickly, especially the stiff variety, you can
probably fire it at low-ish cone 6? Earthenware glaze
is loaded with boron. This is the equivalent of your
firing cone 5 glazes.
Hank Murrow on mon 15 may 06
On May 8, 2006, at 12:27 AM, Ivor and Olive Lewis wrote:
> Dear Hank Murrow,
>
> Which definition do you use to explain the term "Eutectic"
I imagine that the network modifiers(fluxes) disturb(melt) the
silicon/boron/phosphorus glass, and the eutectic trough is that place
where the disturbance is greatest(lowest temperature melt).
>
> <> range. This is because each material brings a different eutectic into
> play and at varying temperatures.>>
Lithium and Boron may start this process, while magnesia and lime bring
their eutectis in later in the melt.
>
> Just being inquisitive!
Me too.
Cheers, Hank
www.murrow.biz/hank
Ivor and Olive Lewis on tue 16 may 06
Dear Hank Murrow,
Thanks for your notes.
I prefer to follow the definitions given by Levin and Co in the ACerS =
Phase diagram book.
I have a firm opinion that once the first liquid forms it become a =
solvent for all of the other ingredients, at least that is, for all =
those that will dissolve. In many cases this first melting ingredient =
will be a Frit or a Borate compound. In many cases for higher =
temperature work it would be the Felspar fraction. This is supported in =
work published by Singer and Singer.
Best regards,
Ivor.
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